Evolution and Biodiversity

Category: predation (Page 1 of 2)

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.

Sticky hunter

Gorareduvius assassin bug is covered in resin

Gorareduvius assassin bug uses resin to capture prey

A Gorareduvius assassin bug uses resin as a tool to overpower prey. That works fine, as Fernando Soley and Marie Herberstein show.

Assassin bugs prey on insects; they grasp them with their forelegs, stab them with their proboscis and suck them out. Insects that are trapped try to escape, of course, but some species of assassin bugs impede that. They coat their body with sticky resin so that prey items cannot escape so quickly.

One of these resin users is an otherwise poorly known Gorareduvius species. It is successful with its sticky strategy, as Fernando Soley and Marie Herberstein show.

Meticulously applied

Gorareduvius lives in Western Australia, where it resides in hummocks of curly spinifex grass, which produces resin. The assassin bug scrapes resin off the grass leaves and applies it meticulously to its body, particularly onto its forelegs. Every individual does it, a Gorareduvius assassin bug is always sticky.

Soley and Herberstein conducted experiments in which they staged interactions between this assassin bug and two types of fast-moving prey: ants and flies. In some trials the assassin bug was allowed to keep its resin equipment, in other cases the researchers gently removed it.

Equipped with resin, Gorareduvius more successfully captures ants and flies, as it turned out. The prey can still escape, but the resin stops them for a while, giving the assassin bug more chance to stab them. As a result, capture attempts of resin-equipped assassin bugs are more often successful than those of clean assassin bugs.


The assassin bug family (Reduviidae) contains about 7000 species. Part of these species cover themselves in resin to enhance prey capture, which the researchers consider as tool use. The habit has arisen at least three times independently.

Willy van Strien

Photo: Gorareduvius, an assassin bug; on the forelegs, above the nod, you see small lumps of resin and where the antennae branch you see the large proboscis. ©Fernando Soley

Soley, F.G. & M.E. Herberstein, 2023. Assassin bugs enhance prey capture with a sticky resin. Biology Letters 19: 20220608. Doi: 10.1098/rsbl.2022.0608
Zhang, J., C. Weirauch, G. Zhang & D. Forero, 2016. Molecular phylogeny of Harpactorinae and Bactrodinae uncovers complex evolution of sticky trap predation in assassin bugs (Heteroptera: Reduviidae). Cladistics 32: 538-554. Doi: 10.1111/cla.12140

Colour meanings

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.


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)

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

Successful as bird dropping

Crab spider imitates fresh bird’s poo

bird-dung crab spider mimics bird's poo

It looks like bird dropping, it smells like bird dropping. But it is the bird-dung crab spider Phrynarachne ceylonica, waiting until an unsuspecting fly comes close, as Long Yu and colleagues show.

Crab spiders get their meals by sitting motionless and waiting for a prey to come within range. Then they may strike suddenly. It helps if they don’t look like a spider while they sit-and-wait, but are disguised. The bird-dung crab spider Phrynarachne ceylonica, for example, successfully mimics a moist bird’s dropping, Long Yu and colleagues write.

The spider not only looks like bird poo, but it also smells like it. It was already known to mislead its predators, such as larger jumping spiders, which simply don’t recognize it.

The spiders occurs in Sri Lanka, China, Japan, and Taiwan.

Leaf miner flies

Now this masquerade proves doubly useful. The sneaky spider attracts tasty insects, mainly leaf miner flies (agromyzids), as Yu notes after observing several juvenile and female crab spiders in the field. The larvae of these flies feed on plant tissue, but adults have a different diet, and to them, fresh bird droppings are a favourite source of nutrients.

Yu painted several spiders entirely white or black, and these painted spiders did not attract the flies.

As he shows, the bird-dung crab spider Phrynarachne ceylonica has the same colours as fresh bird droppings to the eyes of insects. Spinning some threads, the spider mimics a dehydrated edge. And it works out well: insects land right next to the spider. The spider attracts prey at a lower rate than a real bird’s dropping, but that isn’t much of a problem if it is satiated after only one meal.

Unfortunately, the researchers do not report whether the crab spiders do indeed capture and consume the leaf miner flies.

Willy van Strien

Photo: LiCheng Shih (Wikimedia Commons, Creative Commons CC BY 2.0)

Another crab spider mimics a flower

Yu, L., X. Xu, Z. Zhang, C.J. Painting, X. Yang & D. Li, 2021. Masquerading predators deceive prey by aggressively mimicking bird droppings in a crab spider. Current Zoology, online July 24. Doi: 10.1093/cz/zoab060

Game of patience

Snake and frog wait for each other to initiate action

snake should not strike too early

When snake and frog meet, an endurance game begins. The one that moves first takes a risk, as Nozomi Nishiumi and Akira Mori show. If the snake attacks, it will see its prey escape. If the frog jumps, it will be captured.

frog should not jump too earlyAs the snake slowly slides closer, the frog remains motionless. Doesn’t that frog perceive the danger? Or can’t it flee, because it is frozen with fear? Neither, Nozomi Nishiumi and Akira Mori write. The best strategy is to remain motionless as long as possible.
In Japan, the biologists investigated interactions between the Japanese striped snake Elaphe quadrivirgata and one of its prey species, the black-spotted pond frog Pelophylax nigromaculatus. Tension is mounting, as staged encounter experiments showed, because neither animal will take action. And with good reason.


Of course, the frog could initiate flight by jumping away if the snake approaches. But then it is at a disadvantage. Because after take-off kicking, it can’t change his speed and direction. The snake will respond immediately and try to intercept the frog in mid-air, with a good chance of success. So, it is best for the frog to remain motionless.

Also, the approaching snake should refrain from initiating strike behaviour at the frog. Once it has started projecting its head, it can no longer adjust the direction. The frog can evade the strike by jumping away, and chances are high that it will succeed. The snake can make another attempt to capture the frog, but it looses some time because it has to assume the correct posture.

So, the opponents wait for the other to initiate action. The one that gives up first, takes a risk. Sometimes it is the frog that takes pre-emptive action and jumps – with a high chance of being caught. Other times, the snake launches into a strike – and the frog is likely to escape.

No chance

But if both predator and prey persevere, something must happen in the end. At some point they have to switch from waiting to taking action. When the snake has approached the frog to a distance of about six centimetres, the prey has no chance to escape anymore; the snake can successfully grab it. The frog should not wait that long: just before the snake is dangerously close and about to strike, it must jump. That can go wrong, but at least, escape is not yet excluded.

It is a game of patience, but also a game of life and death. In that sense, the tests in which snake and frog are forced to face each other are somewhat cruel, as some frogs were eaten. In nature however, as the researchers state in an ethical note, this is daily practice.

Willy van Strien

Large: Japanese striped snake, Elaphe quadrivirgata. Ʃ64 (Wikimedia Commons, Creative Commons CC BY 3.0)
Small: black-spotted pond frog, Pelophylax nigromaculatus. Alpsdake (Wikimedia Commons, Creative Commons, CC BY-SA 3.0; flipped)

Nishiumi, N. & A. Mori, 2020. A game of patience between predator and prey: waiting for opponent’s action determines successful capture or escape. Canadian Journal of Zoology 98: 351-357. Doi: 10.1139/cjz-2019-0164

Upside-down jellyfish stings at a distance

Mucus contains numerous stinging-cell structures

Upside-down jellyfish releases mucus containing stinging cell masses

The water around upside-down jellyfish is dangerous for small animals and itching for snorkelers. Mobile cell structures, released by the jellyfish, are responsible, as Cheryl Ames and colleagues show.

The upside-down jellyfish Cassiopea xamachana doesn’t swim like jellyfish normally do, but settles upside down on muddy soils of mangrove forests, seagrass beds or shallow bays, its eight oral arms with exuberantly branched flaps facing upward. These jellyfish occur in warm parts of the western Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico, often in large groups.

The habit of lying on the bottom is not the only odd trait of this animal. It is also unusual in hosting unicellular organisms inside its body, the so-called zooxanthellae. Like plants, these organisms convert carbon dioxide and water into carbohydrates and oxygen, using energy from sunlight. They donate part of the carbohydrates to the jellyfish in exchange for their comfortable and safe accommodation.

And then there is a third peculiarity: the water surrounding a group of upside-down jellyfish ‘stings’, as snorkelers know. Cheryl Ames and colleagues discovered how the upside-down jellyfish is responsible.

Mobile cell structures

The carbohydrates that upside-down jellyfish receive from the resident microorganisms are the main source of energy. But the jellyfish also need proteins. That is why they supplement the diet with animal food.

To capture prey, jellyfish use stinging cells. These cells contain stinging capsules, ‘harpoons’, and are filled with a poison blend; the harpoons are able paralyze or kill small critters. Their stings also scare off enemies.

Upside-down jelly has stinging cells on its oral arms. The animal is pulsating, causing water movements that drive prey to the arms, where it is trapped. But, unlike other jellies, the upside-down jellyfish also is able to sting at a distance. How?

If prey is around or if the jellyfish is disturbed, it releases large amounts of mucus, which contain microscopic spherical bodies with an irregular surface, as the current research shows in detail. The bodies consist of an outer cell layer, with stinging cells and ciliated epithelial cells. The content is gelatinous like the jellyfish itself; often zooxanthellae are present, but whether they are active and provide carbohydrates is unknown.


The cell structures, which the researchers have termed cassiosomes, are produced in large quantities on the jellyfish’s arms. Whenever disturbed, the jelly starts emitting them after five minutes in a mucus cloud and continues for hours. Thanks to the cilia, the spherical bodies are motile. They swim around in the mucus for fifteen minutes and then sink down. They go on rotating and displacing for days, and gradually become smoother and smaller to eventually disintegrate after ten days.

The cassiosomes are capable of killing prey animals, laboratory tests show. Brine shrimp, for example, is often instantly killed upon contact with the cell structures.

While doing their work, the researchers experienced that the water in the test tanks was indeed stinging.

Of all peculiarities that upside-down jellyfish possess, this may well be the strangest: loose jellyfish pieces that remain alive for days independently of the main body, move around and help capture prey and scare enemies. The researchers now know that a few closely related jellyfish species release similar small ‘grenades’.

The cell masses in the mucus of upside-down jellyfish had been seen before, at the beginning of the twentieth century, but were thought to be parasites. Nobody could not fancy by that time that it was jellyfish tissue.

Willy van Strien

Photo: Bjoertvedt (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Ames, C.L., A.M.L. Klompen, K. Badhiwala, K. Muffett, A.J. Reft, M. Kumar, J.D. Janssen, J.N. Schultzhaus, L.D. Field, M.E. Muroski, N. Bezio, J.T. Robinson, D.H. Leary, P. Cartwright, A.G. Collins & G.J. Vora, 2020. Cassiosomes are stinging-cell structures in the mucus of the upside-down jellyfish Cassiopea xamachana. Communications Biology 3: 67. Doi: 10.1038/s42003-020-0777-8

Modest carnivore

Shepherd’s purse seedling benefits from animal proteins

Shepherd's purse is carnivorous during early development

Shepherd’s purse seeds derive nutrients from small animals by attracting, ensnaring, killing and digesting them, Hattie Roberts and colleagues discovered. The plant is carnivorous during early development.

Most carnivorous plants have a striking appearance: bladderworts, Venus flytrap, pitcher plants and sundews capture small critters with ingenious traps or sticky leaves. But who would suspect shepherd’s purse of having a carnivorous diet? The plant, which occurs almost everywhere, looks innocent. Still, it captures small invertebrates and uses their proteins when germinating, Hattie Roberts and colleagues write. Apparently, also less spectacular carnivores exist among plants.

Animal proteins

shepherd's purse seeds attract, ensnare, kill and digest small invertebratesA shepherd’s purse plant (Capsella bursa-pastoris) does not capture any bugs, but the seeds do. In moist soil, they are covered with a tough, sticky mucus layer. Years ago, John Barber already showed that germinating seeds excrete an attractive substance that lure small invertebrates, which subsequently are entrapped and killed by a toxin – Barber used mosquito larvae in his experiments. The seeds also release enzymes that digest animal proteins and take up the building blocks, amino acids.

The seeds seem to use animal proteins for growth, Barner stated. They also attract and kill nematodes (roundworms that live in soil), unicellular organisms and bacteria.

Food supply

Now, Hattie Roberts completes the story. She germinated seeds in presence or absence of nematodes and monitored germination and growth of the seedlings. The experiments showed that the seeds do better when animal nutrients are available. In soils in which nematodes were present, more seeds germinated successfully than in soils without nematodes, and the seedlings were bigger and heavier when measured ten days after germination. After three weeks, young plants that had germinated in soil with nematodes had longer roots and larger leaves.

Although seeds of shepherd’s purse are able germinate without animal nutrients, they do better with such nutrients. On soils with low nutrient levels, seeds derive more benefits from animal nutrients than on soils with high nutrient levels, as shown by the experiments.

Shepherd’s purse seeds are small and contain only a minimal food supply for the seedling. That is why the plants profit from extra nutrients during early development.

Willy van Strien

Large: shepherd’s purse flowers. Harry Rose (Wikimedia Commons, Creative Commons CC BY 2.0)
Small: shepherd’s purse seeds. Kinori (Wikimedia Commons, public domain)

See also:
Carnivorous plants with spectacular traps: bladderwort and Venus flytrap

Roberts, H.R., J.M. Warren & J. Provan, 2018. Evidence for facultative protocarnivory in Capsella bursa-pastoris seeds. Scientific Reports 8: 1012. Doi: 10.1038/s41598-018-28564-x
Barber, J.T., 1978. Capsella bursa-pastoris seeds. Are they “carnivorous”? Carnivorous Plant Newsletter 7: 39-42.

Small bites, huge gulps

Thousands of copepods are ingested each day by little auk

feeding in little auk is similar to that of whale

Little auks have a way to gather food that is unusual in birds, Manfred Enstipp and colleagues show. The birds feed ‘almost like a whale’, as the title of  their publication suggests.

The little auk (or dovekie), a seabird species of arctic regions which gathers its food while diving, does not have easy prey to catch. It feeds mainly on copepods (small crustaceans) and it needs an estimated 60,000 prey items per day. It is difficult to capture these tiny animals, as they respond to threats with fast movements. It’s difficult to grasp something as small like copepods under water anyway: the object is pushed away when you try. How does a little auk get all the copepods it needs?

Just by opening the beak while swimming and filtering the prey from the water, Manfred Enstipp and colleagues assumed. But when they filmed little auks with a high-speed camera in a test pool containing copepods and analysed the footage, their idea turned out to be wrong.


Little auks, as the researchers observed, search for copepods with their eyes. Upon prey detection, they go after it, stretching their neck. They extend their gular pouch so that under pressure arises in the oral cavity, and open their bill slightly. As a consequence, a big gulp of prey-laden water is sucked in. The bird then retains the prey while it expels the excess water through the nostrils and from the back of the bill. The whole procedure takes about half a second. By capturing prey in quick succession – and with some luck it sometimes has two items in one trial – a little auk gathers its food.

Many fish species use this ‘suction-feeding’ method to catch prey, but for a bird it is unusual. It is reminiscent of the way baleen whales feed: they take in large quantities of water and expel it through the baleens, retaining the plankton.

Willy van Strien

Photo: Allan Hopkins (via Flickr, Creative Commons CC BY-NC-ND 2.0)

Enstipp, M.R., S. Descamps, J. Fort & D. David Grémillet, 2018. Almost like a whale – First evidence of suction-feeding in a seabird. Journal of Experimental Biology, online May 29 mei. Doi: 10.1242/jeb.182170 

Collateral benefit

Bird disperses eggs of stick insects it swallowed

brown-eared bulbul disperses eggs of stick insects

Some stick insects are even more like plants than you might think at first glance. Just like plant seeds, the eggs can be dispersed by a bird, Kenji Suetsugu and colleagues show.

Stick insects are perfectly camouflaged: they do not stand out among the plants. Yet insect-eating birds are able to find them and will eat them. And that is the end of the story for such tiny animal.

Well, it may not be, Kenji Suetsugu and colleagues report. If an unfortunate female stick insect is carrying mature eggs, a few of these appear undamaged in the bird’s droppings, and some may even hatch.


The researchers, working in Japan, point out that the eggs of stick insects resemble plant seeds: they have the same size and colour and feel the same thanks to a hard shell. Hence their suggestion that the eggs might survive passage through a bird’s digestive tract like plant seeds do. Many plant species produce fruits that are eaten by birds or other animals; the seeds remain intact, are excreted and germinate. Is something similar possible for the eggs of stick insects?

eggs of stick insect after passage through a bird's digestive tractTo find out, they mixed mature eggs of three stick insect species with an artificial diet and fed this to a brown-ear bulbul, one of the main predators of the insects. Afterwards, they examined the bird’s droppings under a stereomicroscope and discovered a small number of intact eggs, and from some of these eggs a young stick insect hatched later on.

Such scenario is also possible when a bird swallowed a gravid female, the authors think. The youngsters that hatch after passage through a bird’s guts would have to find an appropriate food plant to live on, but that is always the case. Normally, a female just drops her eggs to the ground and does not provide any care.


young stick insect, hatched from egg that passed through a bird's gutsSo, sick insects not only look like plants, but they also exhibit a surprising plant-like trait: dispersal of offspring by birds, which is unique in insects.

Dispersal by an avian predator is only possible for species that reproduce parthenogenetically, for in that case females carry eggs that can develop without fertilization. A number of stick insect species exhibit parthenogenesis, including the species that were studied here.


Dispersal of insect eggs via a bird’s digestive tract is not entirely comparable to dispersal of plant seeds. Plants produce fruits that have to be eaten to disperse their seeds. In contrast, a female stick insect has no intention to be captured by a bird to have her eggs transported – by being camouflaged, she tries to prevent just that. But if she is unlucky enough to become a bird’s meal, it is a collateral benefit if some eggs survive and young hatch, if only a few.

The hard eggs probably have not evolved to facilitate avian dispersal, the authors suggest, but to decrease the risk of attack by parasitoid wasps, which lay their eggs in other insects’ eggs.

Stick insects are immobile. Thanks to the birds they may reach new places to live. An interesting question is whether distribution patterns in the insects, to be unravelled by DNA research, overlap with birds’ flyways; that would strengthen the idea that the eggs are sometimes dispersed like plant seeds.

Willy van Strien

Large: Brown-eared bulbul (tongue visible). Alpsdake (Wikimedia Commons, Creative Commons BY-SA 4.0)
Small: stick insect (Ramulus irregulariterdentatus) eggs that passed through a bird’s digestive tract and a young stick insect that hatched from such egg. ©Kenji Suetsugu

Suetsugu, K., S. Funaki, A. Takahashi, K. Ito & T. Yokoyama, 2018. Potential role of bird predation in the dispersal of otherwise flightless stick insects. Ecology, online May 29. Doi: 10.002/ecy.2230

Deceit, abuse and benefits

Complex relationships between arum, blowflies and lizard

Dead-horse arum flower is attractive to lizard

With its smell of rotting carrion, the dead-horse arum Helicodiceros muscivorus is irresistible to blowflies and a lizard. The blowflies will be abused, the lizard benefits. Ana Pérez-Cembranos and colleagues unraveled these complex relationships.

On islands in the Mediterranean Sea, a plant occurs with a very bad smell, the dead-horse arum, Helicodiceros muscivorus. Its odour contains chemical components that are also emitted by a decomposing dead animal. It irresistible to a female blowfly searching for carcasses to lay her eggs on to make sure that the carnivorous larvae will have food. The dead-horse arum takes advantage of that behaviour.

The plants release their odour on the first day of blooming. Blowflies that perceive the smell cannot ignore it. Upon approaching the source, they find a pink or red curved bract, the spathe, with the hairy end of the spadix (inflorescence), which produces the smell. When they land, the spadix turns out to be warm. To blowflies, the imitation is perfect: this is rotting carrion. Guided by the heat, they crawl into the tube that is formed by the base of the spathe around the lower part of the spadix, which bears female and male florets.


Once inside, the blowflies don’t find what they need, which is decaying meat. But if they want to leave, they cannot. Spikes on the spadix keep the door closed. The blowflies are trapped.

Unintentionally, they provide a service to the arum during their imprisonment in the floral chamber. The female flowers at the bottom of the spadix are blooming this first day, and blowflies that had been misled by the arum before, now deliver the pollen that they picked up on that occasion. The plant has its female flowers pollinated.

The next day, the female flowers have faded and the male flowers are mature. The stench and the heat disappear, the spikes wilt and the blowflies escape, and while passing the male flowers, they are loaded with pollen. And here is the second benefit to the plant: the blowflies take the pollen with them to female flowers elsewhere – if at least they find another foul smelling arum on their way and are again misled into visiting it.

So, the blowflies are coerced to pollinate the dead-horse arum without receiving any reward such as nectar. On the contrary: they lose time that they should have spent on searching for genuine carcasses.


Now Ana Pérez-Cembranos and colleagues show that the Balearic lizard Podarcis lilfordi is also misled by the arum’s odour. The animal is omnivorous and sometimes forages on carcasses, which are also attractive as a heat source; lizards are cold-blooded and when the weather is cool, they may use a rotting carcass as a perching site for basking. In addition, they capture the blowflies that arrive at the cadaver in search for a site for oviposition.

The lizards respond to the smell of the dead-horse arum as they do to the smell of a carcass and will approach the source. If that turns out to be a dead-hors arum instead of a dead animal body, they will not find a meat meal, but they do find a basking place and blowflies, which they take from the spathe or grab from the tube. The lizards thus take away a number of pollinators, but, according to the researchers, enough are left to ensure pollination.


So, the lizard isn’t an enemy of the arum. And after the flowering period, when fruits are ripe, a mutualism even develops between both. The lizards consume the fruits and disperse the seeds in their faeces; passage through the lizard’s intestine increases the probability of germination. On Aire Island, a the small island off the southeastern coast of Menorca, where the research was done, the dead-horse arum is a newcomer. It is estimated to have grown there for only about fifty years. In that period, it spread rapidly over the island and nowadays it locally occurs in great densities. That is because of the lizard, which has learned to eat the fruits and now is the main disperser of the seeds, the researchers think.

Willy van Strien

Photo: Balearic lizard on the spathe of the dead-horse arum © Ana Pérez-Cembranos

Pérez-Cembranos, A., V. Pérez-Mellado & W.E. Cooper, 2018. Balearic lizards use chemical cues from a complex deceptive mimicry to capture attracted pollinators. Ethology  124: 260-268. Doi: 10.1111/eth.12728
Angioy, A-M.,  M. C. Stensmyr, I. Urru, M. Puliafito, I. Collu & B. S. Hansson, 2004. Function of the heater: the dead horse arum revisited. Proceedings of the Royal Society London B 271: S13-S15. Doi: 10.1098/rsbl.2003.0111
Stensmyr, M.C., I. Urru, I. Collu. M. Celander. B.S. Hansson & A-M. Angioy, 2002. Rotting smell of dead-horse arum florets. Nature 420: 625-626. Doi: 10.1038/420625a

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