From so simple a beginning

Evolution and Biodiversity

Safe under the covers

28 October 2025 / / 0 Comments

A stinkbug (Megymenum gracilicorne) mother covers her eggs with fungal hyphae

Females of Megymenum gracilicorne culture fungi in an organ on their hind legs

Females of the stinkbug Megymenum gracilicorne protect their eggs in a surprising way, namely with fungal threads they grow on their hind legs, as Takanori Nishino and colleagues discovered.

A striking white, woolly patch can be seen on both hind legs of adult females of the stinkbug Megymenum gracilicorne. It resembles a hearing organ, like some insects have, and the initial assumption was that it was used to perceive sound. But that is not the case, as Takanori Nishino and colleagues demonstrate. Through a multifaceted study, they investigated what the structure is, and they discovered it to be a specific organ that had never been found before.

So, what do we see on the female hind legs and what is its function?

Fungal culture

The bug Megymenum gracilicorne lives in Japan on wild plants of the cucumber family. It sometimes becomes a pest in cucumber and pumpkin cultivation. The researchers show that the structure on the hind legs of females consists of a thick and rigid cuticle with about 2000 pores. On the inside, this cuticle is lined with a layer of glandular cells that connect to the pores and secrete sugar-rich substances. Fungi grow from the pores, creating the white, woolly patch.

This means that the hind legs of females carry a nutrient-rich habitat for fungi. Adult females cultivate fungi on their hind legs, so to speak. They don’t do this without reason, of course. What benefits do the fungi provide to the bugs?

Parasitic wasps repelled

The bugs transfer the fungi to their eggs, the surface of which is covered with sugars, the researchers saw. Each time a female lays an egg, she scrapes fungal threads from one hind leg with the tip of the opposite one and smears them onto the egg. She lays the eggs in a row. After a few days, such a row is fully overgrown with fungus.

The fungus appears to protect the eggs of Megymenum gracilicorne from parasitic wasps. Given the opportunity, these wasps lay their eggs inside the bug eggs; after hatching, the parasitic wasp larvae then consume the eggs’ contents. Although parasitic wasps are attracted to fungus-covered eggs, their ovipositors cannot penetrate a thick layer of fungus to deposit an egg. Thus, the fungus does not deter the predator by its odour but forms a physical defence.

In exchange for sugars and shelter they get from the bug, the fungi provide protective material for the bug eggs: a form of symbiosis. The white structure on females’ hind legs is a hitherto unknown external symbiotic organ, and this collaboration between stinkbug and fungi is new to biology.

Collect

When young stinkbug nymphs hatch, they are covered in fungi. But they lose it during their development, and an adult female must collect fungi to culture. She is not very choosy, so the researchers found multiple fungal species on each female’s hind legs. However, she is careful enough not to select pathogenic fungi. How she manages to avoid these is still unknown.

Willy van Strien

Photo: Megymenum gracilicorne female. The white line on the hindleg is the fungus-growing organ. ©Minoru Moriyama

Source:
Nishino, T., M. Moriyama, H. Mukai, M. Tanahashi, T. Hosokawa, H-Y. Chang, S. Tachikawa, N. Nikoh, R. Koga, C-H. Kuo & T. Fukatsu, 2025. Defensive fungal symbiosis on insect hindlegs. Science 390: 279-283. Doi: 10.1126/science.adp6699

Two species, nevertheless brothers

23 September 2025 /

Messor ibericus queen produces sons of a different species

Two species from one mother: Messor ibericus and Messor structor

Queens of the Iberian harvester ant Messor ibericus have four types of offspring: not only workers, queens, and males of their own species, but also males of another species. Biologically impossible? Yannick Juvé and colleagues explain how it became reality.

Colonies of the ant Messor ibericus in Southern Europe are home to a queen, workers, and males of Messor ibericus – but also males of another species: Messor structor. This is odd, as colonies of Messor structor are absent from most areas where Messor ibericus lives. For instance, on Sicily, where the nearest Messor structor colony is on the mainland, more than 1,000 kilometres away.

It was a mystery how this could happen, but the solution that Yannick Juvé and colleagues now propose is no less puzzling. They discovered that these structor males are sons of the ibericus queen, and therefore brothers of the ibericus males.

It could not get any crazier, although in biology, you are never sure.

Mama’s boys

It will not be a surprise that there is a complicated story behind this. Yet it is an understandable story. Just keep in mind that ants, like bees and wasps, have an unusual system for sex determination.

In most animal and plant species, each individual, male or female, has two sets of chromosomes, small bodies in the cell nuclei that contain the hereditary material DNA; one set comes from the mother, the other from the father. Eggs and sperm each have one set of chromosomes, and after fertilization, a new individual develops with a double set, inheriting characteristics from both parents. But this is not the case with ants, bees, and wasps: females (queen or worker) have two sets of chromosomes, while males have only one. This is because males develop from unfertilized eggs. They are therefore literally mama’s boys; they have no father.

A queen mates with one or more males, stores the sperm and later lays eggs which she may or may not fertilize.

In two steps, Messor ibericus deviated from this pattern.

Hybrid workers

The first step was that an ibericus queen mates not only with males of her own species, but also with those of another species, Messor structor. She stores both types of sperm, and she can apparently distinguish between them. Eggs fertilized with ibericus sperm produce young queens, while eggs fertilized with structor sperm produce workers, which are hybrids with DNA from an ibericus mother and a structor father. If a queen does not mate with a structor male, she cannot produce workers and is unable to establish a colony; interspecies matings are necessary.

It is weird – and it is amazing that fertilization with sperm from another species is possible – but it happens in some other ant species as well. Such species exploit males of another species. These males gain nothing from it, because their sperm only produces worker bees, which do not reproduce. It is sperm parasitism.

Seed eaters

A quick aside: why do ibericus workers have to be hybrids? One hypothesis is that this allows for a distinction between queens and workers. In species with regular, that is, non-hybrid, workers, there is no genetic difference between queens and workers. The difference in form and behaviour that both types of females exhibit as adults is a consequence of the food they receive as larvae. Future queens receive a higher-protein diet, with a greater proportion of animal matter. But Messor species are harvester ants; they collect and eat exclusively seeds. This makes it difficult to differentiate in the diet of female larvae. A genetic difference is then helpful.

And because workers, not queens, are produced with foreign sperm, hybridization does not compromise the inheritance of the ants’ own DNA. Queens, which reproduce, are 100 percent ibericus.

Trick

Back to the main story. The production of hybrid workers was the first step towards the unusual lifestyle of Messor ibericus. It worked, but it confined the species to the area where Messor structor lived. Further dispersion was impossible.

To become independent of the presence of Messor structor, ibericus queens took a second step, Juvé now discovered: they produce structor males themselves, alongside males of their own species. And that step is unique.

Ibericus queens produce structor males by laying eggs with a nucleus that contains only a paternal set of chromosomes. They retrieve this set from a structor sperm cell they have in storage. This requires a trick that has not yet been clarified. Queens may either strip eggs of maternal DNA before fertilization or destroy it afterwards. The result: a son; in this case not a mama’s boy, but a foreign child. It sounds simple, but it must have been difficult to match the foreign paternal chromosome set with the maternal cell machinery.

Domesticated

Once successful, ibericus queens always had structor males in their colony to produce workers and new structor sons. Messor ibericus was no longer restricted to the presence of Messor structor and now has a much larger distribution range.

In the areas where the two species coexist, part of France, Switzerland, and northern Italy, ibericus queens still mate with structor males from structor colonies.

But elsewhere they produce two types of sons: hairy ibericus sons and nearly hairless structor sons. The structor males are an integral part of the life cycle of Messor ibericus. They are isolated from their own species; they do not encounter them, and even if they did, they would not be able to mate with a structor queen. They form a completely domesticated lineage.

Mutual parasites

While structor males initially were abused as sperm suppliers that could not produce fertile offspring themselves (the first step), the situation took on a new dimension after the second step. Domesticated structor males do have offspring that can reproduce: their sons. The ibericus colony ensures this reproduction, so the domesticated structor males are also parasitic themselves. Dependency and parasitism have become mutual.

What seemed biologically impossible, does exist. Apparently, in evolution, everything even remotely conceivable – no matter how improbable or complex – will eventually come into existence.

Willy van Strien

Photos: Males of two species from the same mother: Messor ibericus on the left and Messor structor on the right. Photo from the researchers (Creative Commons CC BY 4.0)

Sources:
Juvé, Y., C. Lutrat, A. Ha, A. Weyna, E. Lauroua, A.C. Afonso Silva, C. Roux, E. Schifani, C. Galkowski, C. Lebas, R. Allio, I. Stoyanov, N. Galtier, B.C. Schlick-Steiner, F.M. Steiner, D. Baas, B. Kaufmann & J. Romiguier, 2025. One mother for two species via obligate cross-species cloning in ants. Nature, 3 September online. Doi: 10.1038/s41586-025-09425-w
Romiguier, J., A. Fournier, S.H. Yek & L. Keller, 2017. Convergent evolution of social hybridogenesis in Messor harvester ants. Molecular Ecology 26: 1108-1117. Doi: 10.1111/mec.13899

Lights in a spider web

15 September 2025 /

Ensnared fireflies lure others into the trap

Spider Psechrus clavis with fireflies in her web

The Taiwanese spider Psechrus clavis will not immediately consume a firefly that has flown into her web. That is because the insect’s lanterns still glow for an hour, attracting even more tasty fireflies, Ho Yin Yip and colleagues write.

Fireflies exchange sexual messages with light produced by chemical reactions in special organs in their abdomen. The winter firefly Diaphanes lampyroides from Taiwan is an example. Males and females use light signals to locate each other. It is an effective communication system.

The Taiwanese spider Psechrus clavis exploits this sexual signal. If a glowing firefly lands in her web, she uses it to intercept more fireflies.

Glow

Fireflies are also called glowworms. Both names are misleading, as they are neither flies nor worms, but beetles (family Lampyridae). Adult females have no wings, and lying on the ground at night, they emit light to attract males; depending on the species, they do this continuously or intermittently. Males locate females by flying around. In some species, males do not emit light; in others, they produce a constant glow, and in still others, they emit series of flashes to reveal their presence.

Male firfly Diaphanes lampyroides

In Diaphanes lampyroides, both males and females emit a constant glow in the dark. Males have two ‘lanterns’, females have four.

For the spider Psechrus clavis their light comes in handy.

Decoy

Psechrus clavis is active in the dark. Females weave an irregular sheet-web horizontally above the ground. It was already known that the white silk of the web and the yellow stripe on the abdomen of the spider, which hangs below the web, attract insects, particularly moths. Now, it appears that the catch is greater when male fireflies are ensnared in the web (female fireflies never end up in a web, since they do not fly).

The researchers observed that the spider simply leaves such a firefly hanging, while she immediately consumes any other prey. The two lanterns of a captured male firefly continue to glow for an hour. And this light attracts other male fireflies, many of which will also fly into the web. Field experiments with LED lights in spider webs confirm the attractivity of the light.

By sparing a male firefly and using it as a decoy, Psechrus clavis catches more of these beetles. A clever strategy.

The question is why male fireflies are attracted to a glowing male in a Psechrus clavis web. Aren’t they looking for females? Probably, males have difficulty distinguishing the two immobile lights of a captive male from the four lights of a stationary female; the lights are the same colour. It is better then to approach all immobile lights than to miss a chance to encounter a female.

Manipulation

Another question is why a man caught in a web keeps glowing. Its light is of no use anymore. Perhaps, the researchers write, it is a response to danger: fireflies also use their lights to deter predators. Or perhaps the spider forces him to keep glowing.

The latter seems unlikely. But Xinhua Fu and colleagues described exactly such a case of coercion last year. Their research concerned another Asian spider, namely Araneus ventricosus, which is also active at night and weaves an orb web. One of this spider’s prey species is the firefly Abscondita terminalis, a species in which immobile females regularly broadcast single-pulse light signals with one lantern, while flying males produce flash trains with two lanterns.

A male’s behaviour changes radically once he has flown into the web of Araneus ventricosus. He starts emitting light signals that mimic those of a female: single-pulse flashes emitted from a single lantern. Other males are attracted to this signal and also become ensnared – to the spider’s advantage.

Apparently, the spider Araneus ventricosus manipulates the captive male, but it is unknown how. She uses venom to paralyze prey, and researchers hypothesize that her bite or venom affects the nervous system of a captive male firefly in such a way that it switches to an abnormal, feminine light signal.

Willy van Strien

Photos:
Large: the Taiwanese spider Psechrus clavis with fireflies in her web. ©Tunghai University Spider Lab
Small: winter firefly Diaphanes lampyroides, male. LiCheng Shih (via Flickr, Creative Commons CC BY 2.0)

Sources:
Yip, H.Y., S.J. Blamires, C-P. Liao & I-M. Tso, 2025. Prey bioluminescence-mediated visual luring in a sit and wait predator. Journal of Animal Ecology, 27 August online. Doi: 10.1111/1365-2656.70102
Fu, X., L. Yu, W. Zhou, C. Lei, R.R. Jackson, M. Kuntner, Q. Huang, S. Zhang & D. Li, 2024. Spiders manipulate and exploit bioluminescent signals of fireflies. Current Biology 34: PR768-R769. Doi: 10.1016/j.cub.2024.07.011
Lai, C-W.,  S. Zhang, D. Piorkowski , C-P. Liao & I-M. Tso, 2017. A trap and a lure: dual function of a nocturnal animal construction. Animal Behaviour 130: 159-164. Doi: 10.1016/j.anbehav.2017.06.016

Race against overheating

4 September 2025 /

Namib Desert beetle cools down by running fast

Namib Desert beetle runs to cool down

The Namib Desert beetle withstands the heat of the sun-drenched desert by running. Carole Roberts and colleagues explain this unexpected fact.

The Namib Desert beetle, Onymacris plana, regularly sprints across the scorching sand of the Namibian desert dunes when the sun is shining and there’s no wind. You might think this wouldn’t turn out well: the creature would overheat. But Carole Roberts and her colleagues show that the beetle actually loses heat by running. How strange!

The beetle is about 2 centimeters long and black, has a horizontally flattened body, long legs, and fused elytra, so it cannot fly. These animals forage during the day for food, blown-in organic matter, and males also search for females. The dunes in the Namib Desert are sparsely covered with grasses and shrubs. Therefore, the beetles cannot remain in the shade all the time but must venture out onto the open sand.

Fatal temperature

That sand is often very hot. The surface temperature can reach as high as 70°C. Namib Desert beetles must be able to withstand this.

It helps that the animals stand high on their legs, with their bodies a centimeter and a half above the surface. It’s 10 to 15 degrees cooler there. But they would still quickly overheat in the sun, Roberts calculates. Male beetles heat up 6 degrees Celsius per minute from the sun’s radiation, females 4 degrees. When they walk or run, the exertion adds another degree. An animal that starts with a comfortable body temperature would reach 50°C within minutes and succumb, because that temperature is fatal.

But this doesn’t happen. That is: as long as the animal keeps running.

High speed

The researchers managed to measure the beetles’ body temperature using a tiny thermometer attached to a long wire. A beetle standing still in the sun – they tested this on dead animals – does indeed warm up quickly. But a running beetle cools down, as it turned out.

A Namib Desert beetle runs at a speed of almost 1 meter per second. That is fast for its size. It maintains this speed for 50 seconds on average, covering over 40 meters.

The researchers theorized that the air passing over its body during such a sprint takes heat away. The flattened body dissipates heat easily. Air flowing past removes more heat than solar radiation and exertion add, resulting in the beetle cooling down. Lab tests confirmed this idea.

The Namib Desert beetle is, as far as we know, the only animal that loses heat by running as fast as it can in the sun when there is no wind. A few insects are known to cool down by flying, the authors write, following the same principle.

Willy van Strien

Photo: Namib Desert beetle Onymacris plana. Lidine Mia (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Source:
Roberts, C.S., E.L. McClain, M.K. Seely, D. Mitchel, V.L. Goodall & J.R. Henschel, 2025. Beetling the heat – the diurnal Namib Desert beetle Onymacris plana cools by running. Journal of Experimental Biology 228: jeb250379. Doi:10.1242/jeb.250379

Fish without males

15 July 2025 /

Amazon molly is a sexual parasite

In Amazon molly, only females exist.

All Amazon mollies are female. A female mates with a male of another species—and then gives birth to daughters that are clones of herself. What sustains this sexual parasitism? Waldir Berbel-Filho and colleagues solve a piece of the puzzle.

The tropical fish Poecilia formosa, the Amazon molly, has a peculiar sex life. The species consists only of females that reproduce asexually: they produce daughters that are genetic copies of the mothers. However, a female must mate with a male to initiate the development of the embryos. Since there are no males of their own species, she will mate with a male of a related species. His sperm triggers the development of her eggs, but his genetic material (DNA) is sidelined. He does not contribute to the genetic make-up of the offspring.

Amazons thus sexually parasitize males of other species. Researchers like Waldir Berbel-Filho and his colleagues are puzzled by how this situation can persist.

Hybrid

The Amazon molly is a freshwater fish averaging about 5.5 centimetres in length that lives in southern Texas and northeastern Mexico. The species is a hybrid, resulting from a single mating event of a male Poecilia latipinna (sailfin molly) and a female Poecilia mexicana (shortfin molly). These parental species are the ‘hosts’ on which the Amazones sexually parasitize.

Where Amazon mollies live, typically only one of the parent species is found, either the sailfin molly or the shortfin molly. The silvery-gray females of all three species look quite similar, but they differ in body shape: the shortfin molly is longer and thinner than the sailfin molly, and its shorter dorsal fin is inserted more posteriorly. Amazon mollies are intermediate in body shape between the two parental species, but their shape varies across locations.

Miracle

Hybridization occurred 100,000 to 200,000 years ago, meaning that the Amazon molly has gone through approximately 500,000 generations.

That’s a miracle. Because male sailfins and shortfins that mate with an Amazon do not sire any offspring, you’d expect them to learn to distinguish between an Amazon molly and a female of their own species and avoid mating with an Amazon molly. But if they would mate only with females of their own species, the Amazon molly can’t reproduce and becomes extinct.

In addition, the Amazon molly competes with its parental species for food; the fish mainly eat algae and small insects. And because Amazons only have daughters, their populations can grow twice as fast as those of the parental species, which produce equal numbers of sons and daughters. The Amazons could therefore displace the parental species, but then, due to a lack of males, they also perish.

Body shape

It seems like a hopeless situation. To explain why Amazon mollies still manage to survive, Berbel-Filho investigated three possibilities.

First possibility: to attract males, Amazons in each location most closely resemble females of the parental species that is present there. So, where they coexist with sailfin molly, they resemble female sailfin molly, and where they coexist with shortfin molly, they resemble female shortfin molly. In other words, they deceive males through mimicry.

Second possibility: to diminish competition for food, Amazon mollies differ from females of the parental species that they coexist with. If that parental species is sailfin molly, they resemble female shortfin mollies, and vice versa. The underlying idea is that a different body shape is associated with a slightly different diet, so that species with different body shapes at least have some of the available food for themselves, and the species can coexist.

Third possibility: the shape variation of Amazon mollies is random and independent of the parental species with which they occur.

Detailed measurements showed that the second possibility is correct. Amazon mollies are less similar in body shape to females of the parental species with which they coexist. The conclusion is that Amazons do not displace the locally present parent species through food competition, although it still needs to be proven that a difference in body shape indeed reduces competition for food.

Waste

But then there is the other danger: the danger that males of the parental species won’t mate with Amazons. The difference between females in each location helps males distinguish the sexual parasite from their own species. Previous research has shown that males indeed mate more often with females of their own species. So how does the Amazon molly manage to survive?

There is no clear answer to that yet. It could be, I think, because females differ on average. The fish vary in body shape, and there is some overlap between females of the local parental species and Amazons. If males were so choosy as to avoid any mating with an Amazon, they would also reject some females of their own species and miss out on paternity. If the amount of sperm they produce isn’t limiting, they’d be better off wasting some sperm to the wrong females than losing fertilisation opportunities with good ones.

Willy van Strien

Photo: Amazon molly, Poecilia formosa. ©Tyler Reich

Sources:
Berbel-Filho, W.M., M. Tobler, T. Reich, A. Eghbalpour, M.J. Ryan, K. Heubel, F. Garcia-De León & I. Schlupp, 2025. Converging or diverging? Shape coevolution between a sperm-dependent asexual and its sexual hosts. Proceedings of the Royal Society B 292: 20250432. Doi: 10.1098/rspb.2025.0432
Riesch, R., M. Plath, A.M. Makowicz & I. Schlupp. 2012. Behavioural and life-history regulation in a unisexual/bisexual mating system: does male mate choice affect female reproductive life histories? Biological Journal of the Linnean Society 106: 598-606. Doi: 10.1111/j.1095-8312.2012.01886.x
Riesch, R., I. Schlupp & M. Plath, 2008. Female sperm limitation in natural populations of a sexual/asexual mating complex (Poecilia latipinna, Poecilia formosa). Biology Letters 4: 266-269. Doi: 10.1098/rsbl.2008.0019

Victims of own defence

11 June 2025 /

Assassin bug Pahabengkakia piliceps hunts bees with their own weapon

Pahabengkakia at the entrance of nest of stingless bees

The assassin bug Pahabengkakia piliceps specializes in capturing stingless bees. To do so, it uses the resin with which the bees defend their nest, Zhaoyang Chen and colleagues show.

To protect their nest against small predators such as ants, beetles and spiders, workers of the stingless bee Trigona collina apply drops of plant resin around the nest entrance and guard bees keep an eye on the entrance. The defence is adequate: unwanted visitors are trapped in the resin and can be eliminated. But one predator is unaffected and even sabotages the system: the assassin bug Pahabengkakia piliceps. It uses the resin to catch the bees themselves, Zhaoyang Chen and colleagues write.

The stingless bee Trigona collina lives in Thailand and China. It establishes colonies in cavities in termite nests, soil, trees or, sometimes, walls of buildings. A nest is surrounded by a wall and accessible through a thin tube of wax and resin.

Sticky

The assassin bug Pahabengkakia piliceps goes to this entrance tube and smears its front and middle legs with resin that the bees have deposited there for defence. Remarkably, the bees do not interfere. With the sticky legs raised, the bug then can grasp bees that approach it – and that are faster than it – immobilize them, take them to its hiding place and pierce them with its stylet (rostrum) to suck their haemolymph (insect blood).

But it is not the stickiness of the resin alone that helps him capture bees, Chen discovered. When, in an experiment, he smeared resin on the hind legs and abdomen of an assassin bug instead of the front and middle legs, the bug was less successful in capturing bees. But the guard bees approached it just as fanatic. Why?

Aromatic

The researchers show that resin on an assassin bug emits more volatile substances, and is therefore more aromatic, than resin droplets at the nest entrance. This is because resin that is evenly spread on a moving animal dries out less quickly.

And the strong resin smell works as a lure. It is also released when an animal ends up in a resin droplet and struggles to get loose, a signal to the guards to go for it. The smeared predatory bug imitates that struggle and in doing so, it attracts bees that it can then easily catch with its sticky front and middle legs. It uses the bees’ resin as a tool for its own purpose: to obtain food.

He uses the bees’ defence weapon against them.

Specialist

There are other assassin bugs that catch their prey with sticky legs, but they are not as specialized as Pahabengkakia piliceps, which only has a few species of stingless bees on its menu. Not only does it catch bees with their own weapon, but sometimes it also lays eggs in the bee nest. The young bugs (nymphs) that emerge from these are not recognized as foreign by the hosts because their body shape resembles that of bees. They feed on the brood of the bees and on adult workers in the nest.

Defence mechanisms of Trigona collina can’t get a grip on the specialized predator Pahabengkakia piliceps.

Willy van Strien

Photo: assassin bug Pahabengkakia piliceps at the entrance of a bee nest. © Zhaoyang Chen

Hunting Pahabengkakia piliceps on YouTube

See also: a generalist sticky assassin bug

Sources:
Chen, Z., L. Tian, J. Ge, S. Wang, T. Chen, Y. Duan, F. Song, W. Cai, Z. Wang & H. Li, 2025. Tool use aids prey-fishing in a specialist predator of stingless bees. PNAS 122: e2422597122. Doi: 10.1073/pnas.2422597122
Jongjitvimol, T. & W. Wattanachaiyingcharoen, 2007. Distribution, nesting sites and nest structures of the stingless bee species, Trigona collina Smith, 1857 (Apidae, Meliponinae) in Thailand. The Natural History Journal of Chulalongkorn University 7: 25-34. Doi: 10.58837/tnh.7.1.102916
Wattanachaiyingcharoen, W. & T. Jongjitvimol, 2007. First record of the predator, Pahabengkakia piliceps Miller, 1941 (Reduviidae, Harpactorinae) in the stingless bee, Trigona collina Smith, 1857 (Apidae, Meliponinae) in Thailand. The Natural History Journal of Chulalongkorn University 7: 71-74. Doi: 10.58837/tnh.7.1.102921

Rain call

5 June 2025 /

Chaffinch warns mate if nest is in danger

The chaffinch's rain call is a specific alram call

With his rain call, a male common chaffinch warns its partner of predators that threaten eggs and young, Léna de Framond and colleagues show.

A common chaffinch not only can produce its song with the characteristic flourish at the end, but also an often-melancholic sounding ‘rain call’. This call has nothing to do with coming rain. What does it mean, Léna de Framond and colleagues wondered.

It is a peculiar call, different from the other calls that the common chaffinch (Fringilla coelebs) has in its repertoire. Only a male calls this call; he repeats it every few seconds and continues to do so for minutes. He calls only during the breeding season and from his territory. And, as in songs, there are dialects, or local differences, which means that the call is partly learned. Its function, De Framond writes, was not known until now.

Playback

There are several possible functions. The rain call, like the song, could be a way to charm a female or to defend the territory and scare off rivals. It could serve as a warning signal to other birds when a predator appears. Or it could be a form of communication between male and female.

To find out which of the three possibilities applies, the researchers did playback experiments in a forest. First, they let male chaffinches listen to the chaffinch’s song, his rain call or, as a control, the song of a blackbird. They noted how each male finch responded to the sound offered: did he sing or call, or did he become aggressive.

In another experiment, they played the sound of a predator or the song of a blackbird with increasing intensity to see if that would elicit the rain call. As enemies they chose the Eurasian sparrowhawk, which hunts adult chaffinches and sometimes grasps young, and the carrion crow, which does not attack adult finches but plunders nests. In both playback experiments they noted whether a female or another male was nearby. In addition, they observed the spontaneous behavior of finches.

Nest in danger

These experiments and observations provided clarity about the function of the rain call: the second possibility – that it is an alarm signal – is the correct one. But it is not a general alarm signal. It is specifically aimed at the partner and warns her when the nest is in danger.

This result is consistent with the fact that the male guards and defends territory and nest, while the female builds the nest, incubates the eggs and raises the young; he helps with feeding them, but she does most of the work. And to complete the story: when dad calls the rain call, the young fall silent so as not to attract the attention of nearby predators.

The rain call is often heard. Apparently, life is not without worries for a chaffinch family.

Willy van Strien

Photo: Male common chaffinch. Membeth (Wikimedia Commons, Creative Commons, public domain CCO 1.0)

The rain call of common chaffinch on YouTube

Source:
Framond, L. de, R. Müller, A. Comin & H. Brumm, 2025. Decoding the chaffinch “rain” call: a female-directed alarm call? Behavioral Ecology, online 4 May. Doi: 10.1093/beheco/araf039

All eggs welcome

27 May 2025 /

Caring fathers aplenty in Japanese giant water bug

In Japanese giant water bug, males take care for the eggs.

Males of the Japanese giant water bug take care of eggs – even of eggs that have been fertilized by other males. Publications by Shin-ya Ohba and Tomoya Suzuki describe this exceptional paternal care.

In the Japanese giant water bug, males care for eggs until they hatch, and they meet the need for care adequately, Shin-ya Ohba and colleagues write. This is remarkable, because care for offspring is rare among insects, and care provided exclusively by the father is even more so.

More peculiar, a third of the eggs a male cares for was fertilized not by himself, but by other males, as Tomoya Suzuki and colleagues were surprised to find.

The Japanese giant water bug, Appasus japonicus, lives in freshwater bodies in Japan and Korea. Within the family of giant water bugs (the Belostomatidae) it is only a small one. It grows to a maximum length of 2 centimeters, while there are also species that measure up to 12 centimeters. Paternal care occurs in many species in this family.

Investment

A male Japanese giant water bug begins his caregiving task by inviting a female to mate with him. He advertises himself with an up-and-down movement. After mating, she sticks fertilized eggs on his back, starting in the middle. When she is finished, he looks for another female to mate with. She adds her eggs. After an average of four matings, his back is fully occupied. A male can carry 100 to 150 eggs, a female lays a few dozen at most.

The eggs require careful treatment: on the one hand, the male must keep them wet and on the other hand, expose them to the air to provide them with sufficient oxygen. He gets this done by staying at the water surface and, with a slow pumping motion, holding the eggs now just above water level and then just below water level. It takes a week to a month for them to hatch, depending on the temperature. During this period, the father can hardly swim and forage because of his burden. He also runs a greater risk of falling victim to a predator. The care therefore requires considerable investment.

Because a male is busy with the eggs for weeks, you would expect that the number of available males is limited, and females must fight for a back where they can lay eggs on. But that turns out not to be the case: males keep up well with females’ egg production and there are enough unoccupied places.

Sperm storage

A male allows a female to lay eggs only if he has mated with her, so that he can be the father of the offspring. Still, on average one in three eggs is ‘foreign’: fertilized by another male. This is not what the researchers had expected when they allowed forty animals – twenty males and twenty females – to mate freely in a tank and determined the relationships between hatched young and adult animals using DNA analyses.

The explanation is that females store sperm and can use sperm from a previous partner instead of the male on which she is currently laying her eggs. And so virtually every male cares for young that are not all his own.

But would not only behavior continue to exist that results in a large number of own offspring? Does paternal care for young make evolutionary sense if paternity is so uncertain?

Yes: in the case of the Japanese giant water bug, it is understandable that a male takes care of other males’ offspring. First, most of the eggs he carries will be fertilized by himself. If he does not take care of them, they are lost. Foreign eggs automatically benefit, but that is just the way it is.

Egg carrier is attractive

In addition, females prefer a male that is carrying eggs over a male with an empty back, previous research has shown. So, eggs on his back – whether fertilized by himself or by another male – increase his chances. And perhaps a female that mates with him will later fertilize eggs with his sperm too and stick them on another male. He may carry some eggs of another father, but another male may take care of his offspring.

The preference of females for males that are already carrying eggs is understandable. A male aims to fill his back within a single day, so that all eggs are the same age and will hatch at the same time. If he collects only a few eggs on a certain day, it is not worth the effort to care for them. He removes them, and they die. By choosing a male that is already carrying eggs, a female reduces that risk for her eggs.

Because foreign eggs are hardly an extra burden and increase a male’s attractiveness, the care for other bugs’ young persists. Ultimately, it benefits a male.

Willy van Strien

Photo: Appasus japonicus, male carrying some eggs and female. © Shin-ya Ohba

Sources:
Ohba, S., R. Hayashida & T. Suzuki, 2025. Female-female competition in two giant water bug species. Ecological Entomology, online 19 May. Doi: 10.1111/een.13454
Suzuki, T., S. Ohba & K. Tojo, 2025. Reproductive strategies in paternal care and remarkably low paternity level in a giant water bug. Ecology and Evolution 15: e71316. Doi: 10.1002/ece3.71316
Ohba, S., N. Okuda & S. Kudo, 2016. Sexual selection of male parental care in giant water bugs. Royal Society Open Science 3: 150720. Doi: 10.1098/rsos.150720

Demand for pollen

15 April 2025 /

Bumblebee queens force plants to accelerate blooming

Queen of buff-tailed bumblebee

Early spring is a crucial time for bumblebee queens. Their larvae need pollen while flowering plants are scarce. But bumblebees can accelerate pollen production, Priska Flury and colleagues report.

In mid-March, bumblebee queens wake up from their hibernation. They had mated in fall and stored sperm cells and then spent the winter alone in rest. Now it is time to start a colony. Each bumblebee queen looks for a place, makes a nest, lays eggs in it and feeds the larvae, which grow on a diet of pollen. They pupate and five weeks after the queen started the nest, the first workers emerge and help her. Until then, it is toiling.

And it is precisely during this busy period that only few plants are flowering and pollen for the larvae is difficult to find. That is unfortunate. But bumblebee queens have a special trick. They accelerate the flowering of plants so that pollen becomes available sooner, Priska Flury and colleagues show. They manipulate plants.

Crescents

A bumblebee queen does so by cutting holes in leaves of non-flowering plants, using her tongue and jaws. These holes have a characteristic crescent shape. What exactly happens in the plant is not clear, but the effect is: the plant flowers a few weeks earlier.

The researchers, who work in Switzerland, first investigated in the lab the clipping behaviour of commercially bred queens of buff-tailed bumblebees (Bombus terrestris) on non-flowering specimens of black mustard and tomato. When queens had little pollen in stock, they would make holes. When there was enough pollen, they would not.

They then captured queens of other bumblebee species in the field and tested in the lab whether they also clipped holes when they were deprived of pollen. Of the forty-one bumblebee species living in Switzerland, they tested seventeen, and the queens of twelve species appeared to make holes, including red-tailed bumblebee (Bombus lapidarius), white-tailed bumblebee (B. lucorum), and early bumblebee (B. pratorum). The other species did not cut holes in the lab, but that does not rule out that they do so in the field.

Plants in which queens had cut holes flowered a few weeks earlier than plants that had not been cut. As a control, the researchers themselves made holes in some plants, but that had almost no effect.

Critical period

So, bumblebee queens ‘order’ pollen when they need it. Previous research had shown that workers of a number of bumblebee species make holes in leaves when there is a high demand for pollen to advance flowering. They do so to survive periods with few flowers when bumblebee colonies are growing rapidly. At the end of April, it is over, because from that time on there is always enough pollen to be found.

That bumblebee queens cut holes is probably more important than the cutting behaviour of workers because early spring, whith no workers around, is a critical period. It depends on this period whether a young colony will survive and grow into a large and successful colony.

Workers and queens have special ‘baskets’ (scopae) on their hind legs to store and transport pollen. They need pollen not only for the larvae, but it is also a source of protein for themselves; they get energy from nectar. When collecting pollen and nectar, they pollinate the flowers. Therefore, it will also be an advantage for plants if the flowering coincides with the time that bumblebees are foraging. The manipulation by bumblebees improves synchronization.

Willy van Strien

Photo: buff-tailed bumblebee queen on small-leaved linden. Ivar Leidus (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Sources:
Flury, P., S. Stade, C.M. De Moraes & M.C. Mescher, 2025. Leaf-damaging behavior by queens is widespread among bumblebee species. Communications Biology 8: 435. Doi: 10.1038/s42003-025-07670-3
Pashalidou, F.G., H. Lambert, T. Peybernes, M.C. Mescher & C.M. De Moraes, 2020. Bumble bees damage plant leaves and accelerate flower production when pollen is scarce. Science 368: 881-884. Doi: 10.1126/science.aay0496

Caterpillar look

2 April 2025 /

Young white-necked jacobin defends itself with appearance and behaviour

White-necked jacobin builds cup-shaped open nest

A young white-necked jacobin looks like a caterpillar with urticating hairs and behaves like one. It is to deter its predators, Jay Falk and colleagues hypothesize.

A newly hatched white-necked jacobin hummingbird looks little like a young bird at first glance. It is a hairy creature that lifts its head and shakes it from side to side as soon as something approaches. Only when its mother announces her arrival with a special signal does it behave normally: it opens its mouth wide to beg for food.

The white-necked jacobin, Florisuga mellivora, lives in the Amazon region. The mother builds a nest and takes care of it on her own, as in other hummingbird species. She lays one or two eggs and incubates them. The young hatch after about two weeks and fledge a few days later.

Chick of white-necked jacobin resembles caterpillar

Jay Falk and colleagues suggest that a chick’s peculiar appearance and behaviour are a response to its vulnerable position. It lies in a cup-shaped nest that is exposed on a plant leaf. The mother regularly flies away to eat, leaving the young in plain sight and unattended.

Deterrent

A white-necked jacobin chick first tries not to stand out. Its ‘hairs’ are exceptionally long natal down feathers that grow on its back. They are the same colour as the seed fluff that lines the nest, camouflaging the young bird well. Also, it may be a physical barrier that prevent small predators from reaching its body.

When predators discover and approach the creature despite its camouflage, it has another trick: mimicry. Due to its hairy appearance and the way it shakes its head, the young bird looks like a caterpillar with urticating hairs. There are several types of caterpillars with irritating stinging hairs in the area, and predators prefer to leave them alone.

The extent to which white-necked jacobin chicks benefit from this fear response and deter predators through their imitation needs further investigation. It seems to work, because the researchers saw how a carnivorous wasp that can overpower young birds approached a white-necked jacobin nest. The wasp inspected the nest but made off when the young started playing caterpillar.

Other caterpillar mimics

The behaviour and the long down feathers of white-necked jacobin chicks are unusual. The only other hummingbird species with young that have such feathers is the black hummingbird, Florisuga fusca. This related species also makes an open, cup-shaped nest on a plant leaf, and its young also appear to imitate a caterpillar.

Strange as it may be, these two hummingbird species are not the only birds with young that resemble caterpillars. The same phenomenon has been extensively described for the South American cinereous mourner (Laniocera hypopyrra), whose orange, hairy young mimic a poisonous caterpillar species. The shrike-like cotinga (Laniisoma elegans) also has young that resemble a hairy caterpillar.

Willy van Strien

Photos
Large: white-necked jacobin (male-like female) on nest. Caspar S (Wikimedia Commons, Creative Commons CC BY 2.0)
Small: nest with young and egg. © Michael Castaño-Diaz

More about white-necked jacobin: crossdressing

Sources:
Falk, J.J., M. Castaño-Diaz, S. Gallan-Giraldo, J. See & S. Taylor, 2025. Potential caterpillar mimicry in a tropical hummingbird. Ecology: 106: e70060. Doi: 10.1002/ecy.70060
Londoño, G.A., D.A. García & M.A. Sánchez Martínez, 2015. Morphological and behavioral evidence of Batesian mimicry in nestlings of a lowland Amazonian bird. The American Naturalist 185: 135-141. Doi: 10.1086/679106
D’Horta, F.M., G.M. Kirwan & D. Buzzetti, 2012. Gaudy juvenile plumages of cinereous mourner (Laniocera hypopyrra) and Brazilian Laniisoma (Laniisoma elegans). The Wilson Journal of Ornithology 124: 429-435. Doi: 10.1676/11-213.1

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