From so simple a beginning

Evolution and Biodiversity

Category: defence (Page 1 of 4)

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

Hidden eyes

3 February 2025 /

Eye spots are effective only from a refuge

Eyespots of spicebush swallowtail caterpillar are effective only when he hides.

The eyespots of a spicebush swallowtail caterpillar protect the animal from hungry birds – but only when the caterpillar is concealed, Elizabeth Postema shows.

An older caterpillar of the spicebush swallowtail butterfly Papilio troilus has an appealing swollen head with two eyespots. It is obvious that these eyespots serve to deter predators. But they do so only under special conditions, Elizabeth Postema writes.

Adult spicebush swallowtail

The swallowtail occurs in North America; the caterpillars live on leaves of trees and shrubs such as sassafras and American tulip tree. A common predator of caterpillars is the black-capped chickadee (Poecile atricapillus), a tit species.

Frightening

A spicebush swallowtail caterpillar sitting openly on a leaf is visible; it is green, but in a slightly different shade than the leaf. The eye spots make it even more conspicuous. That is why a caterpillar hides during the day to escape detection by hungry tits and other predators. Lying on the midrib of a leaf with its head turned towards the tip, it exudes silk. The silk dries and shrinks, forcing the leaf to fold around the caterpillar.

But what is the use of eyespots to a hidden caterpillar? Postema assumed that these eyespots are important when a bird peers into a leaf roll or picks it open. It will then suddenly see a snout with two eyes – an imitation of a snake – and be startled by it. Two eyespots that suddenly appear, the idea is, have a completely different effect than two eyespots that are continuously visible from far away.

Caterpillars of modelling clay

She tested this hypothesis with artificial caterpillars. She made hundreds of green caterpillars of modelling clay with and without eyespots and attached them to tree leaves, which she then folded around the caterpillar or not. So, there were four experimental groups: visible caterpillar without eyespots, visible caterpillar with eyespots, hidden caterpillar without eyespots and hidden caterpillar with eyespots. After five days, she looked for her artificial caterpillars and checked whether they showed bite marks from birds.

As expected, she discovered that a leaf roll offers protection. Caterpillars that were sitting on a leaf in the open were attacked more often than caterpillars that were hidden.

Eye spots did not help the visible caterpillars: tits did not care. But caterpillars in a leaf roll – which were already safer – were even better off with eyespots. Eye spots made the chance of an attack smaller. Postema’s assumption appears to be correct.

The conclusion is that spicebush swallowtail caterpillars protect themselves by combining eyespots with a refuge, so that the ‘eyes’ suddenly pop out in the event of acute danger.

Young caterpillars have no eyespots, but use a different defense strategy: predators overlook them because they are brown and resemble bird droppings.

Willy van Strien

Photo:
Large: caterpillar of spicebush swallowtail Papilio troilus. NCBioTeacher (Wikimedia Commons, Creative Commons, Public Domain)
Small: adult spicebush swallowtail. Robert Webster (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Source:
Postema, E.G., 2024. Eyespot peek-a-boo: Leaf rolls enhance the antipredator effect of insect eyespots. Journal of Animal Ecology, online December 25. Doi: 10.1111/1365-2656.14232

Beetle mimics noxious moths

31 May 2024 /

Bats leave tasty tiger beetle alone

Tiger beetles imitate ultrasonic sounds of unpalatable tiger moths

By mimicking the ultrasonic sound of noxious tiger moths, nocturnally active tiger beetles protect themselves against foraging bats, as Harlan Gough and colleagues write.

Some tiger beetles fly at night. It means that they must be afraid of hunting bats, predators that search for prey by emitting ultrasonic (very high-pitched) clicks and deducing from the reflected sound where a tree or a building is – or where a tasty insect snack is flying. This so-called echolocation allows bats to ‘see’ in the dark. Many insects perceive the ultrasonic clicks of an attacking bat and respond by fleeing or diving to avoid the enemy.

There are a few tiger beetles that react differently: they produce an ultrasonic sound in response to an approaching bat. Harlan Gough and colleagues wanted to know why.

Ultrasonic response

The only other insects known to respond with ultrasonic sound to a hunting bat are moths; an estimated 20 percent of moths responds, at a pitch that bats hear well. The sounds have several effects. Some moths disrupt the reflected bat sound by their calls, so that the bat no longer can interpret the noise. Other moths warn with their sound that they are distasteful or poisonous; once a bat has tasted such a species, it will leave it alone from then on. And other, non-poisonous moths benefit from this: they imitate the sound of a noxious species so that a bat let them also go.

And what about the tiger beetles that produce ultrasonic sound in response to a bat? What do they achieve by doing so?

The researchers tested nineteen tiger beetle species, beetles from the Cicindelidae family, from southern Arizona (USA). They exposed the beetles in the lab to the ultrasonic clicks of a bat that is about to attack. Seven of these nineteen species responded with their own ultrasonic sound, all being species that are active at night. The other twelve species stay put at night and therefore do not need to defend themselves against bats.

Tiger beetles and tiger moths

Do tiger beetles flying at night disrupt the echolocation of bats by jamming? No, the authors write, because that would require a more intensive sound (in technical terms: a higher duty cycle) than the beetles can produce.

Is their ultrasonic sound a warning that they are unpalatable? That is also not the case. The beetles do contain a repellent substance, benzaldehyde, which has an almond scent. But bats still like to eat them, as is evident from experiments with the big brown bat, Eptesicus fuscus. Apparently, the concentration of benzaldehyde is too low to deter this predator. The substance may help against small enemies such as ants and robber flies.

Unpalatable tiger moth warns bat predator with ultrasonic sound

Maybe they imitate the ultrasonic sound of noxious moths? To evaluate that hypothesis, the researchers compared the sounds of tiger beetles with existing sound records of sympatric tiger moths, moths of the subfamily Arctiinae, some of which are poisonous. And yes: the sound produced by tiger beetles is similar to that of poisonous tiger moths. The beetles seem to practice acoustic mimicry.

Wings

Moths that produce ultrasonic sounds do so in diverse ways. They have special structures, such as tiny combs. Tiger beetles produce sounds by brushing their beating hindwings along the back edges of the rigid forewings, the elytra. Normally, they hold the elytra up during flight, but to make sound, they lower them slightly.

Definitive evidence for acoustic mimicry by tiger beetles is still lacking. This would require behavioural tests with bats to find out whether they indeed ignore the beetles after having tasted an unpalatable tiger moth.

Willy van Strien

Photos:
Large: Ellipsoptera marutha, Aridland Tiger Beetle, is one of the species that mimics tiger moths. Laura Gaudette (Wikimedia Commons, Creative Commons CC BY 4.0)
Small: unpalatable tiger moth Cisthene martini, Martin’s Lichen Moth. Ken-ichi Ueda (Wikimedia Commons, Creative Commons CC BY 4.0)

Sources:
Gough, H.M., J.J. Rubin, A.Y. Kawahara & J.R. Barber, 2024. Tiger beetles produce anti-bat ultrasound and are probable Batesian moth mimics. Biology Letters 20: 20230610. Doi: 10.1098/rsbl.2023.0610
Barber, J.R., D. Plotkin , J.J. Rubin, N.T. Homziak, B.C. Leavell, P.R. Houlihan, K.A. Miner, J.W. Breinholt, B. Quirk-Royal, P. Sebastián Padrón, M. Nunez & A.Y. Kawahara, 2022. Anti-bat ultrasound production in moths is globally and phylogenetically widespread. PNAS 119: e2117485119. Doi: 10.1073/pnas.2117485119
Corcoran, A.J., W.E. Conner & J.R. Barber, 2010. Anti-bat tiger moth sounds: form and function. Current Zoology 56: 358-369. Doi: 10.1093/czoolo/56.3.358

Egg signature

21 August 2023 /

African cuckoo stands little chance with fork-tailed drongo

African cuckoo is not successful with fork-tailed drongo

African cuckoo females lay their eggs in nests of fork-tailed drongos. They mimic drongo eggs very accurately – and yet drongos recognize more than 90 percent of cuckoo eggs, Jess Lund and colleagues show.

South of the Sahara lives the African cuckoo, Cuculus gularis, which, like the common European cuckoo, lays eggs in the nests of other bird species (one egg per nest) with the intention that foster parents will raise their chicks. The brood parasite targets only a few bird species, of which the fork-tailed drongo, Dicrurus adsimilis, is one of the most important.

But the cuckoo has hardly any success with this important host species, Jess Lund and colleagues show. The intended foster mother usually notices the deception because she has put a ‘signature’ on her own eggs for verification.

It is the outcome of the long evolutionary history that is shared by African cuckoo and fork-tailed drongo. There is a major conflict between both bird species, because the brood parasite fully depends on the services of the foster parent, and the burden on the foster parent is enormous.

Arms race

It starts with the fact that an African cuckoo female destroys a drongo egg after arriving to lay an egg in the nest of a fork-tailed drongo couple. The cuckoo chick finishes the job. It hatches first and pushes the drongo eggs out of the nest; if a chick happens to have hatched already, it is also thrown out. The foster parents lose their entire clutch. And they are busy for weeks with the demanding care of the foster chick.

This conflict with major interests created an arms race. The drongo learned to recognize cuckoo’s eggs and to reject them. In response, the cuckoo developed eggs that increasingly resembled drongo eggs. Currently, the mimicry is almost perfect: in the eyes of drongos, cuckoo eggs look exactly like drongo eggs.

Individual signature

Drongo eggs are hugely variable. The background colour ranges from white to reddish brown, and the eggs can be immaculate, speckled, or blotched. Between eggs of the African cuckoo, the same variation exists. The mimicry is excellent on population level, and the African cuckoo seems to be ahead in the arms race.

But in reality, the fork-tailed drongo is the winner.

That is because a drongo female consistently produces eggs with the same look. Each female has her own characteristic colour and pattern. She puts, as it were, a distinctive signature on each egg for verification: I laid this one. A cuckoo female lays eggs that fall within the drongo variation, but she lays them randomly. Chances are small that she lays an egg in the nest of a drongo female that produces exactly the same egg type. The cuckoo egg usually is aberrant.

Protected

Conducting experiments and using models, the researchers predict how likely it is that a fork-tailed drongo will recognize and reject an egg of the African cuckoo in her nest. And that is more than 90 percent! Without individual egg signatures, that chance would be much smaller. So, the strategy of drongos – great variation between clutches, great uniformity within clutches – is an excellent response to the almost perfect mimicry of cuckoos, protecting the drongo effectively against the brood parasite.

And so, the African cuckoo has little success with this host. A cuckoo’s egg seldomly is accepted. If you consider that about one in five drongo nests is lost during breeding, the brood parasite has an extremely low reproductive success. But apparently, that low success is enough for the species to survive.

Willy van Strien

Photo: African cuckoo. Alastair Rae (Wikimedia Commons, Creative Commons CC BY-SA 2.0)

Sources:
Lund, J., T. Dixit, M.C. Attwood, S. Hamama, C. Moya, M. Stevens, G.A. Jamie & C.N. Spottiswoode, 2023. When perfection isn’t enough: host egg signatures are an effective defence against high-fidelity African cuckoo mimicry. Proceedings of the Royal Society B, online 26 July. Doi: 10.1098/rspb.2023.1125
Stoddard, M.C., R.M. Kilner & C. Town, 2014. Pattern recognition algorithm reveals how birds evolve individual egg pattern signatures. Nature Communications 5: 4117. Doi: 10.1038/ncomms5117

Venom with a history

9 August 2023 /

Asp caterpillar defends itself with bacterial protein

Asp caterpillar Megalopyge opercularisdelivers a painful sting

Flannel moth caterpillars have a venom that is unique among moths and that causes excruciating pain, deterring predators. Andrew Walker and colleagues unlocked the surprising origin of this venom.

Caterpillars of flannel moths have a cuddly appearance: they have a ‘fur’ of long, often curly hairs. But it is not a good idea to touch them, because spines are hidden under the hairs that inject a venom when touched. The result is excruciating pain that can last for hours or days. Flannel moths form the family Megalopygidae, which has about 250 species that live in North, Central and South America. Their caterpillars are known as asp caterpillars or puss caterpillars.

Certain proteins in the toxic blend of the caterpillars are responsible for the pain. These proteins have a special evolutionary history, Andrew Walker and colleagues discovered.

Holes

The researchers were curious about the composition and mode of action of asp caterpillar venom. They took a closer look at two species: the southern flannel moth Megalopyge opercularis and the black-waved flannel moth Megalopyge crispata. First, they were surprised to find that the toxic proteins, which they call megalysins, closely resemble toxic proteins from disease-causing bacteria, such as Clostridium. The bacterial proteins are harmful because they puncture victims’ cells. And in experiments, the toxic proteins of asp caterpillars turned out to do exactly the same: they punch holes in animal nerve cells. The nerve cells then fire signals that cause the sensation of pain.

There are more species of butterflies and moths with venomous caterpillars, but they have very different types of venom. The venom of the Megalopygid family is unique among the Lepidoptera. Isn’t it strange that caterpillars of this family make the same type of toxic proteins as bacteria? Is that a coincidence?

Defence

No, it’s not. An ancestor of butterflies and moths once obtained genes that code for pore-forming proteins from bacteria, and the butterflies and moths conserved these genes (horizontal gene transfer between species occurs seldomly in evolution). Apparently, the proteins are useful for them, but what function they have is not yet known. In any case, they are not used as venom.

That is, except for members of the Megalopygid family. They restored the function of these proteins as venom, with which caterpillars defend themselves against their predators.

Asp caterpillar is mimicked by bird

And that works great. Once an animal has tried to handle an asp caterpillar and got stinged, it will leave similar critters alone henceforth. Young of the cinereous mourner (Laniocera hypopyrra, a South American passerine bird) take advantage of this. They convincingly mimic the appearance and behaviour of an asp caterpillar, and without being venomous themselves, they still deter predators.

Flannel moths aren’t the only animals that use this type of pore-forming bacteria-derived proteins as venom. Some centipedes, cnidarians and fish do as well.

Willy van Strien

Photo: asp caterpillar of southern flannel moth Megalopyge opercularis. Judy Gallagher (Wikimedia Commons, Creative Commons CC BY 2.0)

Researchers explain their work on YouTube

Sources:
Walker, A.A., S.D. Robinson, D.J. Merritt, F.C. Cardoso, M.H. Goudarzi, R.S. Mercedes, D.A. Eagles, P. Cooper, C.N. Zdenek, B.G. Fry, D.W. Hall, I. Vetter & G.F. King, 2023. Horizontal gene transfer underlies the painful stings of asp caterpillars (Lepidoptera: Megalopygidae). PNAS 120: e230587110. Doi: 10.1073/pnas.2305871120
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

Cleaning ants are successful

14 February 2023 /

Metarhizium fungus makes fewer victims

Argentine ant removes sporen of Metarhizium fungus

Ants defend themselves against disease-causing Metarhizium fungus by grooming off fungal spores from each other. Prolonged exposure to that cleaning behaviour makes the fungus less deadly, Miriam Stock and colleagues show.

Metarhizium fungus can quickly spread throughout an ant nest because the ants easily infect each other with fungal spores. But the animals take action to inhibit the pathogen. That does not leave the fungus unaffected, Miriam Stock and colleagues show with experiments.

To counteract the fungus, ants can disinfect nest and brood (eggs, larvae and pupae) with a mixture of formic acid, which they produce in a poison gland, and tree resin. In addition, a sick ant stays away from the brood and spends more and more time outside the nest so as not to endanger its nest-mates. And the animals keep each other clean. If spores of the fungus land on an ant, her nest-mates either groom off the spores, risking infection themselves, or spray them with formic acid.

New spores

These caring nest-mates should act quickly. The spores attach on the affected ant and germinate, after which nothing can be done anymore. The fungus penetrates the body to develop, eventually killing the ant. Then the fungus appears on the cadaver forming spores that make new victims in the next infection cycle.

Conducting experiments with the Argentine ant, Linepithema humile, Stock shows that timely care does indeed help; the presence of other ants reduces the chance that an ant dies after contact with fungal spores.

But, as it turns out, cleaning also causes changes in the fungus.

Metarhizium-fungus adapts

The trials consisted of series in which the Metarhizium fungus passed repeatedly via spores from a dead ant to a new victim. In half of these series, the infected ant was held isolated, in the other half she was accompanied by two nest-mates that could remove the fungal spores. Conducting a final test after ten infection cycles, the researchers allowed the fungus to infect either an isolated ant or an ant with company.

In the final test, fungal lines that had grown on isolated ants caused a lot of mortality among newly infected ants when they did not receive care from others. But fungal lines that had infected ants that were in company of other ants – that could groom them -, had changed. They formed twice as many spores, but nevertheless made fewer victims among ants they came into contact with, even if there were no nest-mates around to help. These fungal lines had become less deadly.

Essential component

And there was something else: the spores of those ‘social fungal lines’ were less well detected and removed by the ants. The researchers discovered that these spores produced less ergosterol; this is a compound that occurs in all fungi and that, apparently, arouses the ants. So, the ‘social fungus lines’ evade defence by the ants.

But this comes at a cost. Ergosterol is an essential component of the spore membrane. The fact that the ‘social lines’ have lower levels of this important component probably explains why they are less deadly.

So, grooming each other to remove Metarhizium fungus spores as ants do is useful in two ways. It works immediately if ants quickly remove spores from a nest-mate, saving her from death. And in the longer term, it makes the fungus less dangerous.

Willy van Strien

Photo: Argentine ants exchanging food. Davefoc (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

See also: ants disinfect their nest with a mixture of resin and formic acid

Sources:
Stock, M., B. Milutinović, M. Hoenigsberger, A.V. Grasse, F. Wiesenhofer, N. Kampleitner, M. Narasimhan, T. Schmitt & S. Cremer, 2023. Pathogen evasion of social immunity. Nature Ecology & Evolution, online February 2. Doi: 10.1038/s41559-023-01981-6
Brütsch, T., G. Jaffuel, A. Vallat, T.C.J. Turlings & M. Chapuisat, 2017. Wood ants produce a potent antimicrobial agent by applying formic acid on tree-collected resin. Ecology and Evolution 7: 2249-2254. Doi: 10.1002/ece3.2834
Bos, N., T. Lefèvre, A.B. Jensen & P. D’Ettore, 2012. Sick ants become unsociable. Journal of Evolutionary Biology 25: 342-351. Doi: 10.1111/j.1420-9101.2011.02425.x
Chapuisat, M., A. Oppliger, P. Magliano & P. Christe, 2007. Wood ants use resin to protect themselves against pathogens. Proceedings of the Royal Society B 274: 2013-2017. Doi: 10.1098/rspb.2007.0531

Colour meanings

3 August 2022 /

Aegean wall lizard with white throat is more brave

Eagean wall lizard with white throat is bold

An Aegean wall lizard with striking throat colour will run off fast when a predator looms, Kinsey Brock and Indiana Madden write.

In Aegean or Erhard’s wall lizard, Podarcis erhardii, different colour morphs exist: the animals have either a white, yellow or orange throat. The lizards can be found on walls in South-eastern Europe, in a dry landscape with tough shrubs. They have several predators: snakes, birds, and mammals.

When a predator appears, a lizard will flee. But that implies that it must stop what it was doing: sunbathing or foraging for food. For that reason, it will not leave until necessary. Kinsey Brock and Indiana Madden wanted to know whether the three colour morphs have a similar flight initiation distance. They checked the distance they could approach a lizard before it ran away.

Careful

The throat colour of the Aegean wall lizard is genetically determined. Most animals, males and females alike, have a white throat; yellow and orange are less common. There are also individuals with mosaic throat colours, but they are rare. Brock and Madden investigated lizards with plain throat colour on the Greek island of Naxos.

You can get most closely to the white-throated wall lizards, they found; lizards with an orange throat run off earliest; yellow-throated animals are in between.

So, animals with an orange throat are the most careful. They also stay closest to a refuge: a crevice in a wall or dense vegetation. And once they fled, they are slower to reappear than animals with yellow or white throats.

It is in line with lab research showing that white-throated males are the most aggressive, bold, and brave.

Striking colour

An orange-throated Aegean wall lizard probably is more wary because it is more detectable. The grey-brown blotchy body has a camouflage colour, but a yellow, and especially an orange throat stands out against the background. This makes it easier for a predator to discover a lizard with an orange throat, so, in turn, it must flee earlier to escape from the enemy.

Willy van Strien

Photo: Male Podarcis erhardii with white throat. Gailhampshire (Wikimedia Commons, Creative Commons CC BY 2.0)

Source:
Brock, K.M. & I.E. Madden, 2022. Morph‑specific differences in escape behavior in a color polymorphic lizard. Behavioral Ecology and Sociobiology 76: 104. Doi: 10.1007/s00265-022-03211-8

Detering owls by buzzing

30 May 2022 /

Greater mouse-eared bat mimics the sound of bees and wasps

greater mouse-eared bat deludes owls by buzzing

Owls avoid the buzzes of angry bees and wasps. The greater mouse-eared bat takes advantage of that fear by mimicking the sound, Leonardo Ancillotto and colleagues show.

A greater mouse-eared bat in stress behaves weird: it buzzes like a startled group of bees or wasps. Leonardo Ancillotto and colleagues noticed this when they handled the animals during their research. They wondered whether the bats mimic the sound of alarmed bees and wasps when they feel threatened by a potential predator to deter it. It was worth a study.

The greater mouse-eared bat, Myotis myotis, occurs in most European countries. Its enemies are owls, which are nocturnal like the bats.

Larynx

To find out, the researchers first analysed sound recordings of buzzing bats and compared that to the buzzing sounds that several species of bees and wasps produce when they are harassed and defend their nests. Among those species were honeybee (Apis mellifera) and hornet (Vespa crabro). And yes: the buzzing sounds were similar, especially to the ears of an owl.

The similarity is remarkable because the sound is created in different ways. Bees and wasps buzz by beating their wings, while bats produce the sound with the larynx.

Next, the researchers conducted playback experiments in which they broadcasted the buzzing sounds of honeybee, hornet or greater mouse-eared bat to a number of barn owls and tawny owls. The buzzing of the bat was most similar to that of honeybee and hornet. In addition, these insects live in tree cavities, in which owls are interested. As control, they broadcasted the communication calls of another bat species, the European free-tailed bat (Tadarida teniotis).

Experience

The owls moved away from loudspeakers that emitted buzzes, whether these were produced by honeybee, hornet, or greater mouse-eared bat. Bat communication calls, in contrast, attracted them. Wild owls, which may have encountered angry bees or wasps and suffered painful stings, were even more averse to buzzing sounds than owls that had been raised in captivity.

Does it make sense that owls, which are nocturnal animals, are afraid of bees and wasps, which are active during the day? Yes, that fear is conceivable. Honeybees fly until late evening in summer and hornets may fly at night, under moonlight or artificial light. Barn owls appear already at dusk, and when they have hungry young to feed, tawny owls sometimes even hunt during the day.

Apparently, the owls are afraid of bees and wasps and the bats delude them. Buzzing like bees or wasps, acoustic mimicry, may be all they can do to escape from their predator.

Willy van Strien

Photo: Greater mouse-eared bat. Kovács Richárd (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Source:
Ancillotto, L., D. Pafundi, F. Cappa, G. Chaverri, M. Gamba, R. Cervo & D. Russo, 2022. Bats mimic hymenopteran insect sounds to deter predators. Current Biology 32: R408-R409. Doi: 10.1016/j.cub.2022.03.052

Valves closed

10 February 2022 /

Blue mussels learn to avoid parasites

blue mussels close their shells when parasites are around

Blue mussels adapt their behaviour when parasitic larvae are nearby, according to research by Christian Selbach and colleagues.

During food intake, blue mussels, Mytilus edulis, run a risk. The bivalve molluscs feed by filtering water. It enters through an inlet and flows over gills, which not only take oxygen from the water, but also food particles, mainly plankton. These particles get stuck on a mucous layer and are transported to the stomach. The water exits through an outflow opening.

With the inflow of water, mussels may ingest larvae of a harmful parasite.

Mussels that encountered the parasite before, have learned to be more careful. If they notice the presence of parasites in the water, they close their valves and stop filtering to avoid further infection, Christian Selbach and colleagues show.

Intermediate host

The parasite, the fluke (or trematode) Himasthla elongata, has a complicated life cycle in which mussels are indispensable. The cycle starts in a bird that lives near or at sea, such as an oystercatcher, common eider, or scoter; in these animals, adult parasites thrive. They mate and produce eggs that end up in the water with the bird’s faeces. The eggs hatch and the larvae, so-called miracidia, are eaten by common periwinkles; the small snails are the first intermediate host.

In the snails, the parasites develop into the next larval stage, the cercariae, which also end up in the seawater. These are the larvae that infect filtering mussels, which are the second intermediate host. Mussels live in the tidal zone, near the coast, where they can form large shell reefs.

After ingestion by mussels, the parasitic larvae form cysts, a resting stage. Infected mussels grow poorly and are vulnerable to predation by oystercatcher, eider or scoter. And that completes the circle: those birds are the primary host. Once a bird has eaten infected mussels, the parasites mature, and the story starts all over again.

Shut off

If infective larvae are present in the water, mussels cannot help ingesting them when filtering. The only thing they can do to avoid infection is to stop taking in water. But that has a price, because it also means that they cannot take in oxygen and food.

Yet they stop, according to Selbach’s experiments in which he exposed mussels to infective larvae. But they have to learn it.

Mussels that have no previous experience with the parasites go on filtering when they are exposed to larvae. But mussels that met the parasite before and got infected, now shut themselves off. They reduce filtration activity and close the valves with the adductor muscles, which costs energy. But apparently, it would be worse to ingest another dose of parasitic larvae.

Now, it would be interesting to find out how the mussels notice that there are infective larvae around; that is still unclear.

Willy van Strien

Photo: blue mussel. Inductiveload (Wikimedia Commons, public domain)

Source:
Selbach, C., L. Marchant & K.N. Mouritsen, 2022. Mussel memory: can bivalves learn to fear parasites? Royal Society Open Science 9: 211774. Doi: 10.1098/rsos.211774

« Older posts

© 2025 From so simple a beginning

Theme by Anders Norén — Up ↑