From so simple a beginning

Evolution and Biodiversity

Purple-crowned fairywren assists dear breeders

purple-crowned faiywren helps parent and potential partner

The number of territories available is limited for purple-crowned fairywren, a small passerine bird that lives in northern Australia in dense vegetation along rivers and creeks. The territories are linearly aligned, are kept all year round and are all occupied. Out of necessity, young birds often stay with their parents for a few years; most breeding pairs have a few male and female subordinates around them. Purple-crowned fairywrens, Malurus coronatus, eat insects; males have a beautiful purple crown during the breeding season.

Subordinates can assist the breeding pair during the busiest time, the two weeks when the young need to be provisioned. But not all of them offer help, and not all helpers work equally hard. Group members that don’t help are still allowed to stay in the group. Niki Teunissen and colleagues investigated under which circumstances group members do or do not help well. They show that a purple-crowned fairywren subordinate ‘knows’ precisely when it pays to be helpful.

The researchers provided birds with colour rings to make them individually recognizable and of each bird, they knew its parents and its brothers and sisters. They observed the behaviour of fifty groups during three breeding seasons.

If young in the nest have the same parents as a subordinate, or share one parent with it, that subordinate will help feed them. And that is worth the effort. Because with help, more young fledge per clutch on average. A helper shares in this greater success, because those young are full siblings or half-siblings. But in the few years that children stick around, both parents may have died or disappeared and been replaced. And sometimes young birds do not join their parents, but another couple. In such cases, the young are unrelated and a subordinate will not help raise them.

Kinship with the young does not fully explain the willingness to help, though, because, on average, group members work harder for a clutch of half-brothers and half-sisters than for a clutch of full brothers and sisters. That seems enigmatic, but something else is going on. Whether a subordinate will support a breeding pair and how hard it will work, also depends on the value that the pair itself has.

When both the breeding male and female are not its parents, it is not going to help feed the young, as we already saw. If both are its parents, it will help; the young are then full siblings. Thanks to this help, the parents reduce their workload. Their chance of survival increases, and so does the chance that a new clutch of brothers and sisters will be produced. This is also a win for the helper.

Things get interesting, the researchers discovered, when one parent is gone and the other parent has a new partner. How hard a resident purple-crowned fairywren will work now depends on which parent is left: the same-sex parent or the other one.

A female purple-crowned fairywren living with her mother and her new partner works much harder than a subordinate in a group with both parents. That is because that new male partner is interesting. If her mother dies, the helper may inherit her place and her partner, become the owner of the territory and produce the next clutch. That’s the main prize!

With a father and a new partner, she has less to gain. That new female partner is of no use to her, in fact: she is a rival if a new male ever comes into play. So, she works less hard.

Likewise, a male fairywren puts in most effort in helping when living with a father with a new partner.

And therefore, a subordinate purple-crowned fairywren works hardest when the breeding pair consists of a parent and a potential mate – which is very sophisticated. Such couple has great value to him or her. That is why he or she often helps provisioning a nest with half-siblings more intensively than a nest with full siblings.

In line with this, the researchers had previously shown that a young purple-crowned fairywren is less willing to join a group with a same-sex stepparent. Subordinates affiliate with parents and a potential mate. Also, when they help defend the nest against predators, it is to protect (half)siblings as well as parents and a potential mate.

Willy van Strien

Photo: Female (left) and male purple-crowned fairywren. P. Barden (Wikimedia Commons, Creative Commons CC BY 4.0)

Teunissen, N., M. Fan, M.J. Roast, N. Hidalgo Aranzamendi, S.A. Kingma & A. Peters, 2023. Best of both worlds? Helpers in a cooperative fairy-wren assist most to breeding pairs that comprise a potential mate and a relative. Royal Society Open Science 10: 231342. Doi: 10.1098/rsos.231342
Teunissen, N., S.A. Kingma, M. Fan, M.J. Roast & A. Peters, 2021. Context-dependent social benefits drive cooperative predator defense in a bird. Current Biology 31: 4120-4126. Doi: 10.1016/j.cub.2021.06.070
Teunissen, N., S.A. Kingma, M.L. Hall, N. Hidalgo Aranzamendi, J. Komdeur & A. Peters, 2018. More than kin: subordinates foster strong bonds with relatives and potential mates in a social bird. Behavioral Ecology 29: 1316-1324. Doi: 10.1093/beheco/ary120
Kingma, S.A., M.L. Hall, E. Arriero & A. Peters, 2010. Multiple benefits of cooperative breeding in purple-crowned fairy-wrens: a consequence of fidelity? Journal of Animal Ecology 79: 757-768. Doi: 10.1111/j.1365-2656.2010.01697.x

Suicide on command

Horsehair worm manipulates mantis with its own genes

Mantis Tenodera angustipennis is host of horsehair worms

Horsehair worms, which live parasitically in various insects during their larval stage, drive their host to suicide. Tappei Mishina and colleagues wondered how they acquired the potential to make this happen.

A striking and gruesome example of parasites that manipulate their host are horsehair worms. During their larval stage, they live in crickets, grasshoppers, and mantises, but as adult worms they live freely in water. To get there, they drive their hapless host to commit a self-destructive act: it jumps into the water. Horsehair worms can disrupt the behaviour of their host so dramatically thanks to genes they picked up from it, Tappei Mishina and colleagues show.

In water, adult horsehair worms (Nematomorpha) mate in a knotted mass of males and females; that is why they are also called Gordian worms. The females then lay eggs from which microscopic larvae hatch. In order to develop further, they must move to insect hosts that live on dry land. The hosts can ingest the larvae directly with their food or via a ‘transporter’, for instance a mayfly. Living in water during its larval stage, this insect is exposed to horsehair worm larvae. The adult mayfly flies out and may be grabbed by an insect host, which then becomes infected with a parasitic horsehair worm larva.


And then, a horror story starts. The horsehair worm larva grows into an extremely thin worm that can reach several times the length of the host. By the time the parasite matures, it forces its host to behave unnaturally. The host, no longer in charge of himself, starts wandering until it comes across water. Then it enters the water body, often with death as a result. If it survives, it will be infertile.

Chordodes horsehair worm is longer than its host

But the worm is in its element. It wriggles out of the insect’s body and starts looking for conspecifics. If the host is attacked by a predatory water insect before the worm is out, it will emerge more quickly. And if the host is swallowed by a fish or frog, the worm manages to escape from that fish or frog also.

How can horsehair worms so dramatically manipulate the behaviour of their hosts, from which they differ greatly from an evolutionary perspective, Mishina wondered.

His research on mantis Tenodera angustipennis and horsehair worm Chordodes fukuii shows that the worm literally took over the biochemistry of its host.

Expression pattern

The researchers first examined which genes are activated or deactivated in the horsehair worm and in the mantis brain, and how this pattern changes during host manipulation. They show that only in the worm does the expression pattern change: during manipulation, many genes are read and transcribed to be translated into proteins that were previously inactive, while other genes are silenced. The worm produces proteins to influence the praying mantis’ brain, is the conclusion.

They then compared genes from Chordodes species with information about known genes and proteins stored in databases. This yielded a surprising result: more than 1,400 genes of the parasites are very similar to genes of mantises. Especially these genes are expressed differently during manipulation; most are more strongly activated, others are suppressed. Other horsehair worm species than Chordodes species, which have other hosts, do not possess these mantis genes.

Horizontal gene transfer

It seems that Chordodes has picked up genes from its hosts, mantises, over the course of its evolutionary history – and not just a little. That happened not once, but many times. It is not surprising that the proteins encoded by these genes have an effect in mantises.

Gene transfer between animal species, which is called horizontal gene transfer, is a special and, as far as we know, very rare phenomenon. The researchers suggest that it may also play a role in other cases of host manipulation.

Willy van Strien

Photos: ©Takuya Sato
Large: mantid Tenodera angustipennis
Small: mantid Tenodera angustipennis and Chordodes horsehair worm

A horror video with horsehair worms on YouTube

Mishina, T., M-C. Chiu, Y. Hashiguchi, S. Oishi, A. Sasaki, R. Okada, H. Uchiyama, T. Sasaki, M. Sakura, H. Takeshima & T. Sato, 2023. Massive horizontal gene transfer and the evolution of nematomorph-driven behavioral manipulation of mantids. Current Biology, online 19 October. Doi: 10.1016/j.cub.2023.09.052
Sánchez, M.I., F. Ponton, D. Missé, D.P. Hughes & F. Thomas, 2008. Hairworm response to notonectid attacks. Animal Behaviour 75: 823-826. Doi: 10.1016/j.anbehav.2007.07.002
Ponton, F., C. Lebarbenchon, T. Lefèvre, D.G. Biron, D. Duneau, D.P. Hughes & F. Thomas, 2006. Parasite survives predation on its host. Nature 440: 756. Doi: 10.1038/440776a
Biron, D.G., L. Marché, F. Ponton, H.D. Loxdale, N. Galéotti, L. Renault, C. Joly & F. Thomas, 2005. Behavioural manipulation in a grasshopper harbouring hairworm: a proteomics approach. Proceedings of the Royal Society B 272: 2117-2126. Doi: 10.1098/rspb.2005.3213

Promotion for buff-tailed bumblebee worker

If the queen is lost, a worker can take over

When the queen is lost, a buff-tailed bumblebee worker can take over

Normally, buff-tailed bumblebee workers do not mate. But if the queen disappeared, they may mate, Mingsheng Zhuang and colleagues show, enabling the colony to survive.

A bee queen mates and lays eggs; fertilized eggs develop into females, unfertilized eggs into males. Her workers, also females, refrain from reproduction; they defend the nest, care for the brood and forage for food. Thanks to this strict division of labour, a colony runs well. If workers also would produce eggs, too little work would be done. Because the offspring of the queen are related to each other, workers have indirect reproductive success. They do not have a spermatheca, the vesicle in which females store sperm after mating, and are unable to mate. Once a worker, always a worker.

At least, this is how it is in honeybees.

But it does not apply to all bee species that live in colonies with a division of labour between queen and workers, so-called ‘eusocial’ species. In bumblebees (which belong to the bees), workers do have a spermatheca.

It was a mystery why. Now, Mingsheng Zhuang and colleagues argue that bumblebee workers sometimes are promoted to queen.

Artificial insemination

Zhuang shows that workers of several bumblebee species have a spermatheca that is functional. When he artificially inseminated workers, they responded in the same way as queens. They laid fertilized eggs from which daughters emerged and founded a colony. He thinks that workers of all bumblebee species still have a functional spermatheca, even though bumblebees have existed as a eusocial group for tens of millions of years.

The logical next question is whether bumblebee workers can actually mate and function as queens. And under what circumstances they will do.

The researchers conducted much of their research on the buff-tailed bumblebee, Bombus terrestris. This species, which occurs in Europe, North Africa, and parts of Asia, has colonies that exist for one year. In the spring, each queen that has mated and hibernated starts a colony on her own. She makes a nest in the ground, lays eggs and takes care of the larvae that hatch. These larvae develop into workers. Once they are present, the queen is dedicated to laying eggs. The colony grows to a size of hundreds of workers.

At the end of the season, the queen lays eggs from which males develop, and young queens appear. Workers also will lay eggs then, which are unfertilized and produce males. Young queens leave, mate and search a place to hibernate. Males and workers die.


Buff-tailed bumblebee workers normally do not mate. But they can, as experiments of Zhuang show, if they have been separated from the queen and egg-laying workers for a while. In this regard, they differ from young queens, which do not need such a period of isolation. And if a worker has been in the company of nest mates for more than 24 hours before isolation, a switch is not possible anymore. So, opportunities for promotion are limited. Moreover, the chance of workers surviving a mating appears to be small.

But it may be enough to be able to provide a replacement and rescue the colony if a queen dies prematurely, Zhuang and colleagues think; that chance is probably quite high. In that case, workers will lay eggs that develop into early males and if one of the workers takes over the role of queen, mating and producing daughters, the colony can finish the season. According to them, this explains why workers have retained a functional spermatheca. It is difficult to determine whether such replacement often occurs in the wild, they write. It would require locating and digging out colonies and conducting DNA research.


Why doesn’t a worker leave the natal colony and start her own? She would have to leave soon after eclosion, meet a male and survive the mating. But workers are much smaller than queens and produce fewer eggs. Being part of a large colony as a worker will yield greater reproductive success than heading a small colony as a queen.

Willy van Strien

Photo: Buff-tailed bumble bee queen on small-leaved lime. Ivar Leidus (Wikimedia Commons, Creative commons CC BY-SA 4.0)

Zhuang. M., T.J. Colgan, Y. Guo, Z. Zhang, F. Liu, Z. Xia, X. Dai, Z. Zhan, Y. Li, L. Wang, J. Xu, Y. Guo, Y. Qu, J. Yao, H. Yang, F. Yang, X. Li, J. Guo, M.J.F. Brown & J. Li, 2023. Unexpected worker mating and colony founding in a superorganism. Nature Communications 14: 5499. Doi: 10.1038/s41467-023-41198-6

Only when the weather is cool

Lancet liver fluke turns ant into zombie, but not during the day

lancet liver fluke manipulates ant into clamping onto a blade of grass

Larvae of the lancet liver fluke, a parasite, have to transfer from ant to deer. They manipulate the behaviour of infected ants to maximize the chance of transmission, Simone Nordstrand Gasque and Brian Fredensborg report.

An ant carrying lancet liver fluke larvae is no longer itself. At the parasite’s command, it climbs up in the grass and stays there motionless. This makes it more probable for the parasite to reach the host in which it matures, a grazer. The manipulation is complex, as Simone Nordstrand Gasque and Brian Fredensborg show: an infected ant only remains high up in the vegetation when it is chilly; when it is warm, it comes back and behaves normally.

The lancet liver fluke (Dicrocoelium dendriticum, a flatworm) has a complicated life cycle with three larval stages in three different hosts; it cannot live outside a host. It develops successively in a land snail, an ant, and a grazing mammal, such as a deer, sheep, or a cow. So, it has to transfer several times.

Bile ducts

adult lancet liver fluke lives in bile ducts of grazers

Adult liver flukes live in bile ducts in the livers of grazers. They mate and produce eggs that are excreted with the feces. The eggs are picked up by a land snail that nibbles on the droppings. The eggs hatch in the snail’s body into so-called miracidium larvae. They multiply asexually and thousands of larvae of the next stage, the cercaria larvae, appear. They migrate to the snail’s lung where they are packed in slime balls.

The snail coughs up the slime balls, and then it is the turn of the next host, which also comes by itself: the slime balls are tasty snacks for ants, which take them with them to their nest. Adult ants and larvae consume the balls and become infected. In ants, the cercaria larvae develop into the next stage, the metacercaria larvae.


Now comes the most difficult transmission, which is necessary to complete the cycle: from ant back to grazer. That doesn’t happen easily. Ants reside in their nest or walk around on the ground. A grazer does not take a bite of that. The cycle could stop here, but now the parasite intervenes.

The larvae – there may be hundreds of them –safely encapsulate in the ant’s abdomen. But one of them moves to a ganglion in the ant’s head. It is unclear exactly how it manages, but this larva gains control over the ant’s behaviour. Like a zombie, the ant climbs up a blade of grass for no reason and locks its jaws to the vegetation. And so, a grazer may ingest the ant with the larvae on board along with the grass.

The larva that enabled the transfer dies in the grazer’s stomach. It sacrificed itself for the others, which emerge from their capsule in a safe place, develop into adult worms and settle in the bile ducts of the grazer: the circle is complete.

It is extraordinary that a parasite changes the behaviour of its host so drastically. But the lancet liver fluke does even more: it makes sure that the change is only expressed when it makes sense.


Gasque and Fredensborg conducted research into the behaviour of the European red wood ant (Formica polyctena) after infection with lancet liver fluke in woods in Denmark, where roe deer live. They show that an infected ant only stays high up in the vegetation when it is cool, i.e., early in the morning and in the evening. During the day, it unlocks its jaws, goes down and behaves like the other ants.

It turns out that the temperature determines whether an infected ant is itself or becomes a zombie. Time of day, humidity and amount of sunlight do not matter. The warmer it is, the fewer infected ants persist in their biting behaviour. Only on chilly days at the end of the season, do many infected ants stay attached to vegetation all day.

This is beneficial from the parasite’s point of view. Because on hot days an exposed ant could overheat and die, and then the parasitic larvae would not survive either. Since deer mainly graze at dusk, there is no point in taking that risk. It is better to release the ant and let it ant behave normally, and only send it back up again in the evening.

Willy van Strien

Large: infected European red wood ant, Formica polyctena. ©Simone Nordstrand Gasque
Smal: lancet liver fluke (Dicrocoelium dendriticum), adult. D. Drew (Wikimedia Commons, Public Domain)

Gasque, S.N. & B.L. Fredensborg, 2023. Expression of trematode-induced zombie-ant behavior is strongly associated with temperature. Behavioral Ecology, online 24 August. Doi: 10.1093/beheco/arad064

Mutualism, no deception

Smelly Gastrodia orchid provides food for fly larvae

Gastrodia foetida rewards its fly visitors for pollination

For its pollination, Gastrodia foetida, attracts female flies that normally visit mushrooms to lay their eggs on. The orchid seems deceptive, but it is not, Kenji Suetsugu discovered.

Many orchids are cheaters. Whereas most plants cooperate with insects and offer them nectar as a reward for pollination, such orchids have their flowers pollinated without offering a reward in return. They lure their pollinators with false pretences. For example, some orchids mimic female insects to abuse males who want to mate and, in their futile attempts, pick up pollen from one flower and deposit it on another.

Another type of deception is perpetrated by orchids of the genus Gastrodia. They attract fly females who want to lay eggs by mimicking the smell of material in which fly larvae grow up, such as fermenting fruits or decaying mushrooms. But the promise is false, as turns out when females visit these flowers. If they lay eggs on them, which they do occasionally, the larvae that hatch die of starvation.

Gastrodia foetida is an exception, Kenji Suetsugu discovered.


Gastrodia foetida is a rare plant from the forests of Japan and Taiwan. As do other Gastrodia species, the plants have no normal leaves, and the succulent flower does not look like much to us: it is inconspicuous and brown. But to females of some fly species the flower is attractive because of its musty smell; foetida means stinky. A common visitor is Drosophila bizonata, a species with larvae that develop in decaying mushrooms.

Drosophila bizonata carrying pollen

When a female fly enters the flower, the hollow lip in the flower bends up to the column that carries pistil and stamens. The female is stuck in the resulting channel between column and lip. To escape from that trap chamber, she has to crawl through a narrow opening along the stamens, and then the pollen, which is packed in two clumps, gets attached to her back (unless there had been another fly before, because then the clumps are already gone). If she then visits another flower in which she is locked up again, the pollen clumps end up on the pistil and this flower will produce many seeds. In other Gastrodia species, things go in the same way.

Decomposing flowers

But unlike those other species, the stinky orchid really is a suitable place to lay eggs on. Suetsugu frequently found eggs on flowers of Gastrodia foetida that had been visited by a female fly. And surprisingly, the eggs hatch and the larvae do not die, but grow well. Three or four days after pollination, the flowers fall off, leaving only the ovary behind. As the flowers decompose on the soil, the larvae feed on the floral tissue until they mature and pupate. Two weeks after pollination they emerge as adult flies.

Although the larvae of Drosophila bizonata are mushroom eaters, these flowers apparently meet their needs.

Mutual service

It is not clear why mushroom eating fly larvae can also grow well on these flowers. It may have to do with the fact that the orchid cannot make its own sugars through photosynthesis, like normal plants, because it does not have the green leaves necessary for this process. Instead, it steals sugars from fungi. Suetsugu suggests that, as a result, the plant tissue may have chemically similarities to that of mushrooms.

In any case, Gastrodia foetida appears to have gone from deception back to mutualism with pollinators, but with a reward other than nectar. Flies pollinate the flowers, and the succulent decomposing flowers then serve as food for their larvae. It is the first time that this form of ‘nursery pollination’ has been demonstrated.

The mutualism is indispensable for the plant, but not for the fly; it still can lay its eggs on mushrooms also.

Willy van Strien

Photos: ©Kenji Suetsugu
First: Gastrodia foetida
Second: Drosophila bizonata carrying pollen on its back in de flower; the trap chamber (the column above, the lip below) is open

See also:
Gastrodia pubilabiata smells like a brood site for fly larvae, but it is not

Suetsugu, K., 2023. A novel nursery pollination system between a mycoheterotrophic orchid and mushroom-feeding flies. Ecology, online 23 August. Doi: 10.1002/ecy.4152

Shadowing behaviour

Hunting trumpetfish swims closely alongside other fish to remain undetected

By swimming aligned with other fish, the trumpetfish can approach its prey more closely.

By swimming next to another fish, the trumpetfish can approach its prey closer without them noticing. It works, Samuel Matchette and colleagues observed.

In order to ‘surprise’ its prey when attacking, a trumpetfish keeps itself invisible. The elongate, extremely slender fish, typically just over half a meter long, often waits in vertical position between corals and sponges for prey to come close enough to strike; its prey are smaller fish and shrimp. As the predator fish takes on the background colour while waiting, it does not stand out.

But that strategy is useless in water with little cover. In such scenery, the predator applies another camouflage trick: it shadows a harmless fish by swimming very closely alongside it. And that works well, as Samuel Matchette and colleagues show: prey do not see their enemy approaching.

Clear response

The trumpetfish, Aulostomus maculatus, is related to seahorses and pipefish; it lives in the western part of the Atlantic Ocean. It was already known that it often swims aligned with other fish. It arches for instance over the back of a large fish, taking on that fish’s colour. The idea already existed that in doing so, it conceals its characteristic outline to approach its prey undetected. Fish that it hides behind are usually harmless herbivores, such as parrotfish, from which prey animals do not flee. 

But the question still was: does it really work? Does it enable the predator to approach its prey more closely undetected?

On coral riffs near Curaçao, the researchers conducted tests that answered these questions in the affirmative.

They studied the defensive behaviour of bicolour damselfish (Stegastes partitus). These fish live in colonies, are on the menu of trumpetfish and react clearly when seeing a predatory fish: a few individuals inspect the predator and then all quickly seek shelter.


Matchette and colleagues exposed damselfish colonies to a three-dimensional printed and painted model of a trumpetfish alone, a parrotfish alone, or a parrotfish with a trumpetfish attached. They moved those models over a colony, one at a time, and videotaped the colony’s reaction.

As might be expected, damselfish were not much startled by a parrotfish passing on its own. In contrast, they responded strongly to a trumpetfish; they inspected it intensively and then quickly retreated.

And the combination of parrotfish and trumpetfish? This did not elicit a stronger reaction than a parrotfish alone. Conclusion: bicoloured damselfish do not notice a trumpetfish that shadows a parrotfish. The camouflage trick – hiding behind moving fish – works well.

That is: as long as the parrotfish tolerates the company. It often chases the trumpetfish away.

Willy van Strien

Photo: Trumpetfish. Becky A. Dayhuff (Public Domain)

Shadowing behaviour on YouTube

Matchette, S.R., C. Drerup, I.K. Davidson, S.D. Simpson, A.N. Radford & J.E. Herbert-Read, 2023. Predatory trumpetfish conceal themselves from their prey by swimming alongside other fish. Current Biology 33: R781-R802. Doi: 10.1016/j.cub.2023.05.075
Aronson, R., 1983. Foraging behavior of the west Atlantic trumpetfish, Aulostomus maculatus: use of large, herbivorous reef fishes as camouflage. Bulletin of Marine Science 33: 166-171.

Egg signature

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.


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)

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

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.


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?


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

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

Two-spotted spider mite male in a hurry

He strips off her old skin to be the first to mate

A female two-spotted spider mite often is undressed by a male

When a two-spotted spider mite female is about to moult into an adult, a male is often already waiting to undress her and mate, Peter Schausbergen and colleagues write.

Males of the two-spotted or red spider mite, Tetranychus urticae, have to exert every effort to produce offspring, because only the one who is the first to copulate with a female can fertilize her eggs. So, it is important to be present as soon as a female matures. Often, a male is already around before that time, according to observations by Peter Schausbergen and colleagues.

Mites are arachnids. They start life as an egg, become a larva and then go through two nymphal stages. They moult between the stages and emerge from the old skin a bit bigger; after the last moult they are sexually mature. Females develop from fertilized eggs, males from unfertilized eggs.

Silvery appearance

A female two-spotted spider mite is often joined in the last nymphal stage by a male that claims her by sitting on top of her. He spends time and energy on guarding her, and these would be wasted if a rival appears after the last moult and succeeds in mating first. That danger is real, because a newly emerged adult female secretes pheromones that attract males. The guarding male must prevent this.

To shorten the precious waiting time and secure the first mating, a guarding male acts decisively when her final moult is coming. A day before moulting, the nymph enters a resting phase, and in the last few hours she takes on a silvery colour due to air getting between the old skin, which she will shed, and the new skin.

She initiates the moult by bulging, causing the old skin to crack along a crossline. If she is alone, she first pulls off the anterior part of the old skin and then the posterior part, exposing her genital opening. But if a male is guarding, things go different. He drums her back with his forelegs, and in response she bulges earlier. When the old skin has cracked, he quickly strips off the posterior part with his pedipalps (the ‘boxing gloves’ that also spiders also possess). And then, with a bit of luck, he will indeed be the first to mate.

Fighters and sneakers

In our view, this undressing behaviour of the male two-spotted spider mite is very indecent. But he has no choice. Prudent behaviour is punished by natural selection: if he waits patiently for her to undress herself, it is more likely that another male takes over and sires the offspring.

There are two types of guards. Some are fighters, that are often disturbed by other males when they sit on a female and dismount to fight. Others are sneakers, that are not attacked by rivals and are never disturbed. Maybe other males mistake them for females because they do not respond, or maybe they smell like females. It would be interesting to find out whether fighters and sneakers display the same pushing behaviour when the nymph they guard is about to moult.


The two-spotted spider mite is less than half a millimetre long. It feeds by piercing plant cells and sucking their contents. It is a worldwide pest on many agricultural crops. A single mite does little harm, but the bugs multiply quickly and in a brief time, there are many of them.

Willy van Strien

Photo: Two-spotted spider mite female, Tetranychus urticae. Gilles San Martin (Wikimedia Commons, Creative Commons, CC BY-SA 2.0)

Schausberger, P., T.H.H. Nguyen & M. Altintas, 2023. Spider mite males undress females to secure the first mating. iScience, 107112, 7 July. Doi: 10.1016/j.isci.2023.107112
Sato, Y., M.W. Sabelis, M. Egas & F. Faraji, 2013. Alternative phenotypes of male mating behaviour in the two-spotted spider mite. Experimental and Applied Acarology 61: 31-41. Doi: 10.1007/s10493-013-9673-y

Skilful camouflage artist

Cuttlefish has to search for the best pattern

Common cuttlefish is a master of camouflage

The cuttlefish has an excellent camouflage ability and rapidly modifies its appearance when the background changes. But its change is indirect, Theodosia Woo and colleagues show: the cuttlefish adjusts a new skin pattern a few times before it is good enough.

To defend itself against predators, the common cuttlefish, Sepia officinalis, like many other squids, can use camouflage to blend in with its surroundings. And if a predator still detects it, it sprays ink to block the view.

The common cuttlefish lives in the North Sea, the Baltic Sea, and the Mediterranean Sea. Depending on the substrate, such as sand, rocks, or sea grass, it can take on a uniform colour, have a mottled pattern, or have large dark and light skin areas that disrupt its contours. There are countless variations, and the cuttlefish produces an appropriate camouflage against almost any background, Theodosia Woo and colleagues write.

Pigment sacs

This is possible, among other things, thanks to two or three million pigment cells in the skin, the so-called chromatophores. They come in three colours: yellow, red, and brown. The cells are closed sacs with an elastic wall, surrounded by radial muscles. When the muscles contract on command of the brain, they pull the sac open, and the colour becomes visible.

Woo showed how cuttlefish change their appearance by doing experiments in which she provided animals with a changing background; she filmed the skin at high resolution and measured the skin patterns with robust computer software. The result is remarkable. The lightning-fast transition makes it seem as if a cuttlefish realises a new matching skin pattern in one go. But it is not like that.

Confronted with a new background, a cuttlefish immediately starts to adapt its skin pattern. But after a first change, it waits shortly and then adjusts the created pattern to improve it. Then it waits again and adjusts the pattern further, until a satisfying pattern is found. So, it goes through a search process in the blink of an eye and apparently receives feedback continuously. Search trajectories are not fixed, because when the researchers offered the same background change several times, the animals followed different search trajectories and the result was also different. The difference in final skin patterns was so subtle that we cannot observe it.


In addition to the pigment cells that were studied here, the squid skin has two more types of neurally controlled cells that enable changes in appearance. There are cells that, thanks to their nanostructure, reflect light of one specific colour, for example blue: the iridophores. And there are cells that reflect all incident light and are white in daylight: the leucophores. In addition, the skin can be smooth or rough. The sophistication of a squid skin is beyond our imagination.

All these possibilities are not only used for camouflage, but also for communication. Common cuttlefish spend spring and summer inshore to spawn, and the colours the animals display then is an attraction for divers.

Colour blind

The greatest puzzle about squids is how they are capable to mimic their environment so perfectly while being colourblind themselves. Almost nothing is known about this, but there is evidence that small light sensitive organs occur in the skin.

Willy van Strien

Photo: Young common cuttlefish. Magnef1 (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Woo, T., X. Liang, D.A. Evans, O. Fernandez, F. Kretschmer, S. Reiter & G. Laurent, 2023. The dynamics of pattern matching in camouflaging cuttlefish. Nature, online 28 June. Doi: 10.1038/s41586-023-06259-2
Gilmore, R., R. Crook & J.L. Krans, 2016. Cephalopod camouflage: cells and organs of the skin. Nature Education 9(2): 1
Chiao, C-C., C. Chubb & R.T. Hanlon, 2015. A review of visual perception mechanisms that regulate rapid adaptive camouflage in cuttlefish. Journal of Comparative Physiology A 201: 933-945. Doi: 10.1007/s00359-015-0988-5

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