Secrets of the orchid mantis revealed – it doesn’t mimic an orchid after all

15 February, 2015
The orchid mantis, Hymenopus coronatus. Igor Siwanowicz

The orchid mantis, Hymenopus coronatus. Photo: Igor Siwanowicz

An article I originally wrote for The Conversation. Read the original article here.

In his 1879 account of wanderings in the Orient, the travel writer James Hingston describes how, in West Java, he was treated to a bizarre experience:

I am taken by my kind host around his garden, and shown, among other things, a flower, a red orchid, that catches and feeds upon live flies. It seized upon a butterfly while I was present, and enclosed it in its pretty but deadly leaves, as a spider would have enveloped it in network.

Orchid mantis: Hymenopus coronatus
frupus, CC BY-NC

What Hingston had seen was not a carnivorous orchid, as he thought. But the reality is no less weird or fascinating. He had seen – and been fooled by – an orchid mantis, Hymenopus coronatus, not a plant but an insect.

We have known about orchid mantises for more than 100 years. Famous naturalists such as Alfred Russell Wallace have speculated about their extraordinary appearance. Eschewing the drab green or brown of most mantises, the orchid mantis is resplendent in white and pink. The upper parts of its legs are greatly flattened and are heart-shaped, looking uncannily like petals. On a leaf it would be highly conspicuous – but when sitting on a flower, it is extremely hard to see. In photos, the mantis appears in or next to a flower, challenging the reader to spot it.

Hiding in plain sight?

On the face of it, this is a classic evolutionary story, and a cut-and-dried case: the mantis has evolved to mimic the flower as a form of crypsis – enabling it to hide among its petals, feeding upon insects that are attracted by the flower. Cryptic mimicry by predators is well known. For example, crab spiders camouflage themselves against a flower, and can change from yellow to white to match their host flower.

Crab spider (Misumena vatia) with wasp prey.
Olaf Leillinger/Wikimedia

The orchid mantis is something of a poster child for such cryptic mimicry. So obviously true is this evolutionary story that it is often discussed today as established fact.

No one seemed to have noticed that there has been no evidence to support this hypothesis. Orchid mantises are actually very rare in the field, so their behaviour is hardly known about, except in captivity. For example, nobody knows exactly which flower the mantis is supposed to mimic.

Now a set of new studies by James O’Hanlon and colleagues shows quite clearly that we’ve been getting it wrong all this time. While it is indeed a flower mimic – the first known animal to do this – the orchid mantis doesn’t hide in an orchid. It doesn’t hide at all. And to an insect, it doesn’t even look particularly like an orchid.

A deadly lure

O’Hanlon and colleagues set about systematically testing the ideas contained within the traditional view of the orchid mantis’ modus operandi. First, they tested whether mantises actually camouflage amongst flowers, or, alternatively, attract insects on their own. For a flower-seeking insect, as predicted, the mantis’ colour pattern is indistinguishable from most common flowers.

However, when paired alongside the most common flower in their habitat, insects approached mantises more often than flowers, showing that mantises are attractive to insects by themselves, rather than simply camouflaging among the flowers.

“We can clearly observe insects, like bees, diverging from their flight paths and flying right towards this deceptive predator,” O’Hanlon told me. “These beasties are marvellous for this kind of question, because we can observe a dynamic interaction between predators and prey.”

This phenomenon, known as aggressive mimicry, occurs in other animals. The Bolas spider releases chemicals that imitate sex pheromones released by female moths seeking a mate. Male moths, with their elaborately plumed antennae, can detect these pheromones from miles away, and are lured in to their death. Carnivorous Photuris firefly females can mimic the flash-responses of a different species of firefly, attracting amorous males who find themselves on the menu.

Next the researchers assessed where mantises chose to sit. Surprisingly mantises did not choose to hide among the flowers. They chose leaves just as often. Sitting near flowers did bring benefits, though, because insects were attracted to the general vicinity – the “magnet effect”.

Any old flower

When they compared the mantis’s shape and colour with flowers from an insect’s perspective, the predator did not resemble an orchid or indeed any particular species of flower, but rather a “generalised” flower. This fits with what we already know: some of the best mimics in nature are imperfect mimics with characteristics of several “model” species.

Placing experimental plastic models out in the field, the researchers found that mantis colour was much more important than shape in attracting insects. They believe that mantises may not actually precisely mimic a particular kind of flower. Instead they may exploit a loophole created by evolutionary efficiency savings within the insect brain.

Jumping to conclusions

As humans with giant, hyper-developed brains capable of abstract thought, we have the luxury of being able to make decisions using all the available information. After a few seconds of scrutiny, what initially looks like a flower because of its colour begins to look suspicious – and once we spy bug eyes and a vaguely insectoid outline, the game is up: it’s a mantis.

But a tiny insect zipping around on the move, with its compact brain, cannot afford such cognitive extravagance. It has a shortcut – a rule of thumb: anything matching colour X is a nectar-containing flower. More colour equals bigger flower, with potentially more nectar. No cross-checks, no two-step authentication. The mantis takes advantage of this shortcut by using “sensory exploitation”. It is a concentrated mass of the right colour – a supernormal stimulus. The insect classifies the mantis as a giant nectar-filled flower and approaches to investigate – to its doom.

“This work is terrific,” Martin Stevens of Exeter University, an expert on animal deception and mimicry, unconnected with the work, told me. “It’s wonderful to see something that Wallace and others discussed so long ago, finally tested experimentally.”

Colour me beautiful: an orchid mantis nymph devours its prey
Igor Siwanowicz

This is not the first species to lure in prey with sensory exploitation. The white crab spider reflects strongly in the UV, making it highly conspicuous to wandering insects. But the spider still “hides” on a flower. Surprisingly a flower with a crab spider is more attractive than one without: the crab spider mimics UV-reflective floral patterns that guide insects to nectar. But the orchid mantis is the first animal ever shown to mimic an entire flower, attracting insects on its own.

There is one remaining issue, though: if the mantis can attract insects by sensory exploitation alone, muses Stevens, then: “Why have body parts that look like petals? My guess is that the pollinators are initially attracted at a distance through sensory exploitation, but then more accurate mimicry kicks in at close range, when the insects can inspect the mantis more closely for what it is.”

Greg Holwell, who coauthored the study, told me: “What this work really emphasises is that working on a completely unstudied species can produce fascinating results. Getting out there and starting with some solid natural history helps to generate hypotheses that you can subsequently test with field experiments, and can lead to the discovery of completely novel phenomena.”

“While important discoveries are made from laboratory research on model species like fruit flies, every species has an exciting story to tell and can help shape our understanding of how the natural world works.”

Handcuffs, traps and spikes shed light on sex lives of insects

3 July, 2014

A male Mexican true bushcricket, left, grasps female with bear-trap genital claspers. Photo: L Barrientos-Lozano

(An article I originally wrote for The Conversation. Read the original article here).

Handcuffs, spikes and traps – you would think they were part of some bondage aficionado’s bedroom collection. But what are they doing in the insect world?

A new study I worked on sheds light on why some bushcrickets – usually gentle creatures – get pretty violent when it comes to sex, and in the process helps to settle a decades-old debate about their odd mating habits.

In just a few species of bushcrickets, scattered across the evolutionary tree, we found that males have evolved horrific-looking clasping devices near their genitals. They use them to hold females down for as long as possible after sex is done – that is, after they have transferred all their sperm. This results in long mating sessions, up to seven hours in some cases.

Bushcricket claspers are usually simple feelers that engage with pits on the female. But some species use spiked hooks to grab onto the female, often piercing her cuticle. Others have bear-traps, tongs that wrap around her, or even interlocking “handcuffs” that completely encircle her.


Male genital claspers from bushcrickets with relatively normal sex (left) and with protracted sex (right). In Anonconotus (top right) the spike pierces the female’s cuticle; in Phasmodes (bottom right) the interlocking claspers resemble ‘handcuffs’ and completely encircle the female. Photo: Karim Vahed


Females of these species are, perhaps understandably, not down with this. Although they themselves have not evolved any defensive tools, they actively resist by jumping, biting and kicking to dislodge the male – and with a degree of success, because species where females resist have less prolonged copulations than those where they do not.

Why would these males want to restrain their partners, when bushcricket mating is usually relatively peaceful? Female bushcrickets aren’t dangerous to males, unlike in some spiders where, before sex, males gas females or tie them up in silk to avoid being cannibalised. The answer takes us into one of evolution’s most important, but also most secretive, conflicts – the battle over what happens to sperm after mating – and also helps answer a longstanding question about some other odd sexual habits of bushcrickets.

Sperm in a bag

The act of mating itself is only the beginning of a struggle to determine which male actually gets to fertilise the female’s eggs. One in which females play just as active a part as males.

For example, female water striders have a submarine hatch covering their genitals, utterly preventing access. Unwanted males resort to “blackmailing” them into opening this hatch by threatening to attract predators. Other female insects have labyrinth-like vaginas with tortuous twists and blind endings. Some females even actively scoop sperm out of the male.

In most land animals, however, we never actually get to see what happens next, because sperm is placed deep inside the female. Often we have to make guesses about what male and females do with their genitalia, based on their shape. But bushcrickets are ideal study animals to look at the evolutionary fate of sperm.

Male bushcrickets transfer all their sperm in a bag, which then drip-feeds into the female after the male has left. But female bushcrickets can, if they want to, get rid of unwanted males’ sperm by simply removing (and usually eating) the sperm bag before the sperm is completely transferred. Males would naturally rather this didn’t happen, and try to stop it. And because this happens outside the female’s body, we have an opportunity to watch what is going on.

The food of love?

If giving females sperm in a drip-feed bag isn’t weird enough, male bushcrickets normally also produce a giant sticky blob of gel from their genitals, which females proceed to eat. This “nuptial gift” is enormously costly to produce, weighing up to 40% of the male’s body weight.

(To be fair, it could be substantially worse for the male – in sagebrush crickets, for instance, females suck the males’ blood during sex and in striped ground crickets they begin eating his legs.)


Female bushcricket, Poecilimon thessalicus, feeding on a huge nuptial gift given to her by the male. Photo: Gerlind Lehmann

For decades, scientists have debated what this huge nuptial gift, or “spermatophylax”, is for. Some think that the gift is a nutritious meal that helps the female make more, better babies with the male sperm – a win-win situation that is common in the insect world. Especially when food is scarce, females can use the gift as nutrition for making offspring.

But others think that the nuptial gift is also a device for manipulation – ensuring the female is distracted, so the sperm bag gets to drain as much sperm as possiblebefore she gets around to eating it. Gifts contain very poor nutrition – the equivalent of flavoured chewing gum – and are laced with substances that stimulate the female to feed and also make her less likely to mate again afterwards.

Why bushcrickets get kinky

Our new study looks at some of the more bizarre mating habits of 44 species of bushcrickets to work out why in some cases males have resorted to more aggressive practices.

In a scattering of bushcricket species, we found that, over evolutionary time, males have stopped bothering to produce the nuptial gift for females at all.

In every case where the nuptial gift has been lost, males have evolved to protract sex for long periods even after they have transferred their sperm bag, attempting to restrain the female using hooks, tongs or handcuffs while she desperately resists. In cases where males present females with a food gift, though, the decision appears to be more mutual: females do not typically resist sex, and the males’ genital claspers fit neatly into special grooves on the female with no evidence for conflict.


Mating pair of Meconema bushcrickets, female to the left, with male’s genital tongs highlighted in purple (and shown in inset). Photo: C. Roesti

Why do males of these species engage in such violent behaviour? We argue this almost certainly acts to prolong the drainage of sperm from the bag into the female for longer than she wants – the exact same function that had been proposed for the nuptial gift these species have lost. It is highly likely that this restraining behaviour is a substitute for the nuptial gift.

It’s what you do with it that counts

A great many studies of sexual conflict, especially spanning lots of species, focus on the form and complexity of male genital structures in particular – and there are certainly some corkers about.

But our study shows that sexual conflicts don’t necessarily lead to more complex male genital structures. For example, bushcricket male claspers already had simple hooked “teeth” – which usually engage peacefully with pits on the female. Some of our “stingy” males, though, used these same teeth in a different way – holding the female forcefully, piercing her cuticle. Without observing the behaviour, this difference wouldn’t have been obvious.

There is also currently a prevailing view that females are passive or possibly even willing recipients of male attempts to manipulate them. Female genital structures are often not as varied as those of males, and some have pointed to this fact as evidence that there really is no conflict going on. But our study clearly shows that, in this case, females actively and effectively resisted males using simple behaviour – jumping, biting and kicking – and not with specially evolved structures.

Whether you have gin-trap shaped genitals, a giant gift of jelly, or relatively normal-looking sexual apparatus, it is not what you have but what you do with it that counts.

Invertebrates inject a bit of romance during sex – by stabbing each other

26 March, 2014
Bedbug male stabbing a female during sex. Image: Wikimedia

Bedbug male stabbing a female during sex. Image: Wikimedia

(An article I originally wrote for The Conversation. Read the original article here).

It is fair to say we belong to a species obsessed by sex. We are among the only species to have sex for fun, not just for reproduction. For some other species, though, sex is far from fun. In fact, as two recent review papers show, it is a war zone, involving penis fencing and love darts.

In 1897, the Italian zoologist Constantino Ribaga discovered a strange organ in female bedbugs, halfway up the abdomen. He suggested they used it to produce sound, like cicadas. But something wasn’t right: in the bundle of cells underneath this organ he found large quantities of sperm.

The organ discovered by Ribaga, later dubbed a spermalege. Image: Rich Naylor

How did they get there? At the time, puzzled scientists concluded males must flood females with sperm, and the female digested the excess – as a “nuptial gift” – using this organ. But this theory was tenuous at best.

It wasn’t until 1913 that males were observed stabbing females through this organ with a horrifying syringe-like penis, then copulating with the wound. Sperm swim directly to the ovaries through the body cavity. This has been termed “traumatic insemination”.

In the first of the two papers, appearing in Biological Reviews, Rolanda Lange and colleagues at Tuebingen in Germany and Sheffield in the UK show that similar behaviour occurs across invertebrates.

In snails, which are hermaphrodites, amorous advances involve “traumatic secretion transfer”, blasting potential mates at close range with “love darts” covered in psychoactive mucus. Understandably, neither party is keen to play the female role, involving being shot. In sea slugs this results in “penis fencing” – each attempting to penis-stab the other. An inflicted wound inoculates the recipient with sperm.

A brown garden snail (Cantareus aspersus) impales its mate with a “love dart”. Image:Ronald Chase/Proceedings B

Why would a male want to impale the mother of his future children? In a paper in Annual Review of Entomology, Nik Tatarnic and colleagues from Sydney in Australia and Sheffield in the UK focus on arthropods. They explain that stabbing is, in evolutionary terms, a game-changing tactic for males.

To sire offspring obviously requires mating, but this is only a prelude. Much more crucial is fertilisation, and females understandably want to control when, where and by whom their eggs are fertilised.

In many cases females are highly successful at this – by, for example, using their reproductive tract as a powerful tool to screen out all but preferred males. Females often simply eject unattractive males’ sperm, or filter it out chemically, and sometimes can close their tract entirely. Female control is especially widespread in insects, where females store sperm in a sac – sometimes for years, opening it to fertilise eggs at their leisure.


The dragonfly penis is shaped like a spade for removing rivals’ sperm. Image: Jonathan Waage/Science

On the other hand, each male mating with a female would prefer his own sperm to fertilise the offspring. To achieve this, he must both overcome the female’s defences and beat her other mates – two neverending “arms races”.

Males can beat rivals to the first step – that is, mating – by impressing females through courtship. This may also win favour at the fertilisation phase. But males are more sneaky than that, with outlandish adaptations to ensure their sperm win the race, like plugging females up, or scooping out rival sperm. Our own human organ may indeed have a dual function as a “sperm scoop”.


Wood mouse sperm form a snake by hooking on to each other. Image: Harry Moore/ABC

Another solution is to try and directly overcome challenges posed by the females’ reproductive tract. Fruit fly males spike their sperm, drugging females into releasing more eggs, even though this shortens females’ lives. Wood mice females produce mucus that only strong-swimming sperm can cross. Ever resourceful, males’ sperm team up into long “snakes” that, together, altruistically push one lucky sperm through the mucus to success.

Stabbing for the win


Syringe-like bedbug paramere (penis), adapted for stabbing females. Image: Cassandra Willyard/

Penis-stabbing, though, shifts the goalposts entirely. By injecting sperm directly into females’ body fluid, male bedbugs bypass the female’s adaptations to control access to her eggs. The female is injured in the process, reducing her number of offspring. But in the cold language of statistics, this may be worth it for the male – a healthy female is no good if she doesn’t bear his offspring. Males can both prevent females from excluding their sperm and also from preferring other males.


The nightmarish embolus (penis-like organ) of a male Harpactea sadistica spider. Image: Milan Rezac/Science Blogs


This has been such a successful strategy for males that it has evolved repeatedly across the animal kingdom. Male Myzostoma worms secrete corrosive enzymes from their penis, dissolving a hole in the female’s skin into which they ejaculate. Male giant squid inject sperm packets into females’ arms – although occasionally they end up inseminating themselves, literally shooting themselves in the foot. In Harpactea sadisticaspiders, the male bites the female, then stabs her with needle-like genitals, ejaculating into the wound.

In some groups, like “bat bugs”, males spear females at random. In many others, though, females have evolved damage-limiting adaptations such as the bedbug “spermalege” (the organ discovered by Ribaga), offering an easy entry point to discourage indiscriminate stabbing. Some species have entire “paragenital systems” guiding sperm to their ovaries, while the regular reproductive apparatus shrivels from disuse.


Polistes wasp infected with a female Xenos twisted-wing parasite. Her brood canal pokes out for prospective mates, who, mysteriously, often ignore it and stab her instead. Image: Macro Photography/Aculeata Research

Males will often jump on and penis-stab anything that comes their way, even females of other species, often killing them in the process – a phenomenon that has driven some species to evolve apart. Male bedbugs regularly jump other males by mistake – which is such a problem that males in one species have evolved their own damage-control spermaleges.

In an arms race, though, neither side can win – each can only gain a temporary advantage – and, as expected, females are fighting back. Astonishingly, some female bedbugs have evolved modified spermaleges that mimic those of males, to reduce harassment. Others have evolved ways of digesting the injected sperm and using it to repair their wounds, minimising the damage.

The course of true love never did run smooth. For males and females locked in an arms race, though, it could be said to run in circles – vicious ones at that. And all to inject a little bit of romance.

Even among ants, size matters more than shape

29 January, 2014

(An article I originally wrote for The Conversation with some beautiful photos by Alex Wild ( Read the original article).

Myrmecocystus workers: living larders. Alex Wild (

Worker ants are a funny old bunch, of many shapes and sizes. But they tend to get bigger and smaller much more often than evolving entirely new shapes, according to a new study.

While most animals juggle survival with having babies, a worker ant is not constrained by also having to be a functioning mum. She can safely leave that job to the queen ant, because the queen produces the worker’s siblings, who all share her genes and thus pass on her DNA.

Although specially adapted for a life of labour, worker ants nevertheless still come in many different forms. Not constrained by the need to produce offspring, and given the many tasks workers perform, one might imagine this could lead to the evolution of some extremely strangely shaped insects.

At a cursory glance, this seems to be true in spades. Take, for instance, the turtle ant Cephalotes that nests in tree cavities. It has a dedicated caste of soldiers who are supposed to block entrances, and this they achieve by using heads that have evolved to look like manhole covers.

Cephalotes workers: heads shaped like manhole covers. Alex Wild (

Or consider the honeypot ants (shown in the lead photograph), Myrmecocystus, who have abdomens that are giant distended living vats of honey.

There are also Camponotus workers that “explode” on contact with enemies, showering them with glue from a massively overdeveloped gland in their head.

Camponotus worker explodes in an enemy’s face. Mark Moffett ( / Minden Pictures / FLPA

These remarkable examples, however, might just be exceptions. Most worker ants have more mundane-looking features that set them apart, mostly mere variation in size. It is rare for ants to have more than one specialised kind of worker. Even the most complex societies of ants, like leafcutter ants, have at most three truly distinct kinds of workers, and these tend to vary only in size.

This discrepancy intrigued Marcio Pie and Marcel Tschá, from the Federal University of Paraná ‎in Brazil, who have just published a study in PeerJ to find out if size actually varies more than shape. To do this, they took thousands of measurements from technical photographs of worker ants on AntBase, a repository of ant pictures and data.

And indeed it seems, at least among the workers of some 100 ant species they measured, that size was actually much more variable than shape (“shape” being measurements that don’t simply all vary in concert with each other across species).

This fact makes evolution in worker ants less special than we might expect – because variation in size is also how many other groups of animals vary most in their evolutionary history. Despite the many weird and wonderful forms of ants we know exist, it seems worker ants are no different from the rest of us when it comes to how morphology evolves.

In many cases workers of different species differ mainly in size, not shape. Here an Argentine ant (Linepithema, left) attacks a fire ant (Solenopsis). Alex Wild (

So why does size vary so much? One theory is that size represents a “genetic line of least resistance” – ie size seems to be easy to evolve.

In the multilayered webs of interacting genes making up something as complex as an ant, not all genetic combinations exist. Some are more frequent than others. In wild populations, patterns of genetic variation are not random, but fall along well-defined axes that act as channels guiding the way the physical form can evolve. Typically, the most important is a “bigger-smaller” axis. Also, hormones control growth, and can act on many body parts at once. Genetic mutations that change hormone levels can result in big changes in size.

In a slightly more complex twist, some features grow disproportionately as animals get bigger. Just as in Alice in Wonderland, as ants become really small, tiny objects like sand grains become enormous. Under these conditions, long legs for running become less important and stubby legs are an advantage. Thus, legs are proportionally shorter in smaller ants.

And why is it that ant shapes vary so little? One theory holds that what workers lack in specialised forms, they make up for in flexible behaviour, which allows workers to respond to unpredictable environments. Ants are able to reallocate whole sections of the workforce at a moment’s notice when the need arises. For example, African driver ants (Dorylus) form living bridges when on the move, red ants (Myrmica) become undertakers and fire ants (Solenopsis) form living waterproof rafts to see the whole colony through a flood.

Fire ants form living rafts

Another possibility hinges on the fact that ant workers are still technically capable of having offspring, and occasionally try to do so (although their offspring are all male, and are often eaten by other workers). This may mean their forms are still constrained by the need to reproduce, however meagre a brood they end up producing.

Nevertheless, in some cases, specialised ecology has selected for specialised workers. And, in keeping with this, Pie and Tschá did find a few cases of rapid shape evolution in isolated lineages, for example in fungus-farming ants (like leafcutter ants).

Leafcutter ants, Atta cephalotes. Alex Wild (

Shape evolution had also accelerated in another group containing weirdos such as Calyptomyrmex, some of whose members have mysterious spatula-shaped hairs covering their bodies – nobody knows what for.

Calyptomyrmex: covered in mysterious oddly shaped hairs. Alex Wild (

The obvious next question is – does slow shape evolution go hand in hand with flexible, jack-of-all-trades workers like fire ants? Conversely, do we see the fastest shape evolution in lineages where different kinds of workers have specialised, inflexible jobs, like turtle ants? Perhaps studying some more ant pictures might answer those questions.

You lazy, good-for-nothing thrips

7 June, 2013

I thought I’d share some recent and preliminary data from my thrips, which should give a flavour of what I’m doing in the outback.  These are quite tentative, and I’m hoping to increase samples next time I go out.

Dunatothrips build silk nests (see our recent paper), and there are usually between 1 and 4 adult females inside a nest (although this can get up to 20).  If I experimentally damage the nest, the females repair it.  You can see this in this video I took down the microscope:

Notice that one female remains in the background, doing nothing, while the others work hard to add silk to the nest.  I saw quite a few females refusing to help in this way. I recorded which of the females chose to engage in what I assume is risky and costly repair behaviour. I removed the females in the order they began adding silk to the nest, and classified them into “repaired” versus “did not repair”.

Then, I dissected them to see whether they were reproductive (i.e. whether they had developing eggs in their ovaries). I found that females that chose to repair the nest were usually reproductive, while those that did not repair were non-reproductive (see below – I’ve applied some scatter to the points to make the figure clearer).


(The bars show the probability of me finding the female has developing ovaries when I dissect her, given what I have observed of her behaviour).

Thus, some females are neither reproducing nor helping to maintain the nest.  Sounds a bit like human teenagers to me.  Except these are not offspring (the nest hasn’t matured yet, and nests only support one generation of offspring).  They are most probably sisters or near relatives of the reproductives (see this paper here for evidence).

Can we say anything else about these do-nothing thrips at this stage?  I have also found (very tentatively) that you tend to get nonreproductive females in small nests, while in larger nests, everybody reproduces:

prop repro vs volume

If this indeed turns out to be true, maybe the size of small nests stops some females reproducing.  This would make sense, because there is only a limited surface area of leaf to feed on inside a nest.  If we look at the wider sample of nests I’ve collected on all my field trips combined, we can see the pattern of offspring production also supports this idea.  In large nests, more females produce more total offspring.  In small nests, more females do not produce more offspring.

total offspring vs nest size

This suggests that in small nests, some females are neither having their own offspring nor helping their nestmates produce more offspring (in both cases, we would have seen increases in total offspring with numbers of females).

Of course, “lazy” nonreproductives may be helping in ways I can’t detect – perhaps by helping the offspring to feed, by defending against an enemy I haven’t encountered yet, or by maintaining nest hygiene.  In those small nests, the offspring may still SURVIVE better if there are more adult females in the nest.  That’s something I’m going to have to test, maybe by measuring offspring size, or development rate in the field. Alternatively the reproductives might survive better if they don’t have to work as hard when helpers are present, something that would certainly be difficult to test in the field.

The big question is, what determines who gets to reproduce in a small nest?  Intuitively, there should be competition over breeding status, as happens in (for example) paper wasps and joint-nesting ants.  As we described in our last paper, these thrips appear to be pacifists, with no apparent aggression at all.  Also, there’s no evidence that nonreproductive females are smaller than reproductive females from the same nest.  Unless they are conducting some kind of chemical warfare, there is no indication of conflict at all.

In other species, lazy workers are sometimes waiting for a chance to reproduce themselves – the more they work now, the less energy they have for later reproduction.  In Dunatothrips, this is probably not the case because nests probably only have one generation. However, that is not set in stone, and it may be that females in a small nest end up taking turns to reproduce in what we would call a social queue. That would be really exciting because it would make this system quite close to Polistes paper wasps.  These are questions I’m hoping to solve with experiments next time I hit the field.  I am currently thinking about how to design these, and constructive ideas are most welcome!

Associating with ants: a dangerous game

5 April, 2013

Spiders take a leaf out of Spielberg’s book in dealing with potentially deadly adversaries, according to recent research.  “Keep absolutely still.. his vision’s based on movement.

What if you had an unassailable personal army of bodyguards, but who would kill you the instant they knew they could?  What if your only available prey were potentially vicious killers?  You have to be able to catch one, and at the same time avoid becoming an hors d’oeuvre on *their* menu.

Such is the problem for any arthropod that decides to rely on ants for its survival.  To put it mildly, they’re not the world’s easiest, plumpest or least-resisting meal.  They can get a bit, shall we say, argumentative.

But if you can crack it, boy, you’ve got it made.

Plenty of insects have given this a shot – so many that the habit is given its own name, “myrmecophily”.

For example, the butterfly family Lycaenidae have this down to a fine art (explored in this review by Pierce et al 2002).

Liphyra larva. Photo: © Dani Jump

Liphyra larva. Photo: © Dani Jump

Take Liphyra, which I remember most clearly because it was featured on one of David Attenborough’s marvellous programs. The caterpillars are shaped like impregnable tanks and slowly gorge themselves on ant larvae while the ants are helpless to stop them.  Once emerged, the adults are covered in waxy scales that the ants cannot grip, and waltz out of the nest to fly away unharmed.

Some Lycaenids have evolved glands (called “cupola glands”) that secrete perfume that mimics the ants’ own secretions.  Consider for example the caterpillars of Niphanda, which cloak themselves in the perfume of ant larvae, and then sit back and relax as they are enthusiastically fed to adulthood by the ant workers.  Hojo et al (2009) found that the ants would even feed glass beads that had been experimentally rolled in the correct perfume.

Niphanda larva being fed by ants as one of their own. Photo:

Niphanda larva being fed by ants as one of their own. Photo:

Beetles of the tribe Paussini have arrived at a similar set of solutions, reviewed here: some are shaped like little tanks while others cloak themselves in protective chemicals.  In all cases the beetles munch happily away on the ant larvae while the ants can do nothing to stop them.

Spiders can also use chemical trickery: Cosmophasis spiders live within ant nests, again safely cloaked in “Eau de Fourmi” acquired (in a macabre twist shown by this study) directly from the ant larvae on which they feast.

Aphantochilus spiders, although they are not chemically or physically protected, have evolved a very particular set of skills to allow them to pick off individual ants. They are still vulnerable to attack, though, especially when small. Accordingly the mother defends small offspring vigorously against attacks by their future prey.

Protection rackets

Many arthropods use ants as protection.  No-one’s likely to attack you if you are surrounded by thousands of angry, biting micro-warriors.  But the same principle applies; nothing’s stopping those warriors from turning on you.

Aphids, treehoppers and caterpillars provide “protection money”.  They are well-known to be farmed by ants, a great example of a protection mutualism where the insect produces a sticky, sugary “gift” in return for the ants’ protection.  Treehoppers that normally provide parental care known to turn over responsibility for their offspring entirely to ants.  This recent study found that treehoppers can even summon ants using signals made by vibrating their wings when they are attacked by predators.  These associations run so deep that ants will even protect aphid eggs, which do not produce honeydew – in effect the ants are investing effort for a future reward.

Sweet rewards are cheap for aphids and treehoppers (since honeydew is waste material to them) but caterpillars must produce this substance de novo, making it rather expensive.  Lycaenids do this by means of “tentacular glands” (see Pierce et al‘s review).

Extra reading about mutualisms with ants can be found in this chapter of the wonderful book Ant Ecology (OUP, 2010).

The old Jurassic Park trick

Eustala spiders are not so generous.  A new study in the journal Ecological Entomology by researchers Loriann Garcia and John Styrsky shows that Eustala like to keep it simple; no complex chemicals, super-thick armour, or twinkle-toes defence techniques – and definitely no sugary gifts for the ants.

Instead, like that nerve-jangling scene from Jurassic Park, what Eustala does is to stay really, really, really, really still.  Even with ants crawling all over it, feeling and probing it with their antennae.  And the ants don’t notice it.

Keep absolutely still, his vision's based on movement.. Photo:

Keep absolutely still, his vision’s based on movement.. Photo:

By day, Eustala spiders rest on Acacia trees in Panama.  They sit on the thorns, and oddly are not attacked by the ants that swarm over the plant and over the body of the spider.

Why are they not attacked?  The authors did an experiment using both Eustala and Argiope, a spider that lives on ant-free trees.  They placed recently-killed (frozen and just-thawed) spiders of both species onto branches containing ants, and watched what happened.  For comparison, they released moving spiders (still agitated after being handled) of both species onto nearby branches.

Playing sleeping lions… with actual lions

Regardless of species, the immobilised spiders were not attacked, but the moving spiders were.  Moving

Eustala hiding in plain sight. Photo © Loriann Garcia, John Styrsky

Eustala hiding in plain sight. Photo © Loriann Garcia, John Styrsky

Eustala had no particular advantage over moving Argiope.  That shows that Eustala is not primarily relying on any kind of chemical camouflage to defend against the ants.

Furthermore, Eustala had one more trick up its sleeve.  If discovered, Eustala jumped to safety on a line of silk, allowing them to cautiously rappel back up the line once the ant attack subsided and resume their position.  Once in this position, they did not react at all to patrolling ants, even when tickled by ants’ antennae and lunged at by ants’ jaws.

Argiope, on the other hand, tended to try and run away, which further enraged the ants and ended up with them being killed or driven off the plant entirely.

One huge Tyrannosaur or millions of tiny ones: clearly the advice is the same.

Termites measure wood from inside using echolocation

13 January, 2013
C. secundus worker chewing a piece of wood. Image: © Simon Tragust and Tobias Weil/DDP

C. secundus worker chewing a piece of wood. Image: © Simon Tragust and Tobias Weil/DDP

You’re sitting in a cave.  How big is the mountain above you?

A termite would be able to tell you, simply by chewing the wall.

Drywood termites live quite bizarre lives when you think about it.  Next time you hear the loud noises of termites chewing inside a wood block, take a moment to think about how odd their existence must be.

Imagine being completely entombed in a cave made of delicious ham. You live in it, tunnel through it, raise your kids in it, excrete in it.

Wings and eyes are both useless, so you have dispensed with them.

At some point down the line, one generation of your unborn great-grandkids is going to find the ham runs out.  And that’s a problem. They are going to have to fly off and find another mountain of ham that can sustain them and their offspring.

But – and here’s the spicy port-and-molasses rub – you have to know how much ham is left  in order to know when to develop wings and fly away rather than stay and have babies.  And when you find a new mountain of ham, in order to know whether it is a suitable resource for you and your future kids, you have to be able to assess how big it is.

From the inside.

How do termites know how big the wood block is without measuring it?

Some insects walk up and down a resource to measure it, like burying beetles, which walk round a dead mouse several times before deciding whether to breed on it.  That doesn’t work for termites, because predators would quickly snap them up.

An experiment a few years back discovered that Cryptotermes termites actually use a form of echolocation to size up the piece of wood they’re in – and to choose between alternative blocks of wood.

Staggeringly, the termites can sense the vibrations that are caused when they make their loud chewing sounds, and the resonant frequency tells them how big the wood is.

Faced with a choice of 20mm and 160mm blocks of pine, Cryptotermes invariably chose the smaller block (probably because they are small-bodied termites and don’t want to bump into any larger ones).

But when chewing vibrations from the 160mm block were recorded and then played back through the 20mm block, the preference was destroyed.  When control vibrations consisting of random noise were played through the 20mm block, there was no effect on preference.

Other insects communicate using vibrations through wood or other material – for example, treehopper babies “buzz” against their branch in structured collective patterns, using a “cooler!  warmer!” method to direct their mother to the source of a predator attack. Passalid beetle larvae communicate with parents via cicada-style stridulations, while some male dung beetles produce a courtship song that is transmitted by vibrating the poo in which the female is buried.  They say romance is dead…


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