I believe I’ve posted several times about the “orchid mantis,” a term for a variety of mantises that mimic—or appear to mimic—orchids. These mantids are believed to sit among flowers, and resemble the flower so strongly that pollinators like bees try to pollinate them. But instead of getting pollen, the bee gets snapped up by the mantid when they fly into its arms. Here are a few of the mantids showing their resemblance to flowers:
Below is an Attenborough video showing the mantis deceiving a bush cricket, who loses its life. It also shows another cool fact: this species is not mimetic as a juvenile, but aposematic: it has “warning coloration” showing that it’s toxic. For some reason, perhaps connected with the mantis’s increasing size, it changes shape and color as it ages, changing from conspicuous to cryptic.
This is a classic example of “aggressive mimicry,” so called because the purported evolutionary pressure was to get food (through aggression) rather than simply to hide form predators. But, like many cases of mimicry, the “pollinator-deceiving” mimicry is inferred, and hasn’t been scientifically tested. To do that you’d have to experiment on these species (and they’re not easy to come by), showing that pollinators do indeed mistake the mantis for an orchid flower. And to test another hypothesis—that the mantis gains additional camouflage by hiding among the orchids it’s said to resemble—you’d have to show that the mantis gets more prey when it’s sitting among flowers than when sitting alone. That hadn’t been done either.
Further, there’s an alternative hypothesis: that the mantid isn’t camouflaged to deceive prey, but to deceive predators. After all, the aposematic coloration of the juvenile above probably evolved to warn away predators who have learned to avoid the toxicity associated with that coloration. And that implies that something tries to eat these creatures. Finally, the flower-resemblance of the adult could serve to simultaneously deceive both predators and prey.
To test these hypotheses, James O’Hanlon, Gregory Holwell, and Marie Herberstein, a group of researchers from Australia and New Zealand, did experimental tests on insects and flowers in Malaysia. The results appear in the two papers at bottom (with links). What they found is that the conventional wisdom is correct in some respects, but the story is more complicated. I’ll just summarize the main findings. Tests were done on a single species of tropical flower mantid: Hymenopus coronatus. Here’s a photo of a subadult female from the American Naturalist paper:
- Yes, the mantids do mimic flowers, but not necessarily a particular orchid. This conclusion comes from color-spectrum analysis of the insects and flowers filtered through what a pollinator (a bee) really sees. This shows that the mantid resembles the colors of a number of local flowers, but the authors weren’t able to find a specific orchid that the tested mantis resembled. (Note: they didn’t look all that hard.) But given their ability to find mantids sitting around on many flowers besides orchids, and even on vegetation, it’s likely that the mantis evolved to resemble a generalized flower rather than a given species of orchid. This makes more sense because a given species of orchid is not ubiquitous in the rain forests, and they flower irregularly.
- Tests in which the researchers observed pollinators “inspecting” (deviating from a flight path to come closer to an object) a control object (a stick), a common species of flower in the area tied to a stick, and a mantid tethered to a stick showed that pollinators barely visited the stick, visited the flower moderately often, but visited the mantid most often (in fact, several instances of predation were observed). This shows that the mantid by iteself is even more attractive than the flower, so it’s not simply hiding itself among flowers to enhance its resemblance to a flower.
- However, mantis sitting next to flowers got a higher rate of pollinator inspection than did solitary mantises, and the higher the density of flowers around a mantis, the more the mantis was “inspected”—and presumably the more noms it got. Therefore, although mantids can attract pollinators on their own, this ability is enhanced when they’re sitting amongst a bunch of flowers. Because solitary mantises seem more attractive to pollinators than are solitary flowers (implying that the mantids don’t have to hide to deceive the insect), this result probably reflects the fact that a patch of flowers simply draws more insects than do solitary flowers.
- The authors tested, using a Y-tube, whether the mantids chose to go to flowers more often than to leaves, which would imply a form of habitat selection. They found no effect: mantids went down the “leaf” arm of the Y as often as down the “flower arm”. So, though it may be adaptive for a mantid to be drawn to a group of flowers (because it gets more prey), that behavior hasn’t evolved. But a Y-tube test may not be the best way to test habitat selection, as it’s an extremely artificial situation.
So the conventional wisdom confirmed here is that the mantids do resemble flowers, fool predators that way, and can get noms by their resemblance. The conventional wisdom that was overturned is that these mantids resemble orchids, or a specific species of orchid. Also, the results don’t support the notion that the mimicry is imperfect, so that the mantids must hide among flowers to get any prey. They do get more prey when hiding among flowers, but that’s because more pollinators are attracted to large groups of flowers. Finally, the authors found no support for the idea that mantids seek out the flowers and hide among them. Because that behavior would seem adaptive, I’d like to see better tests, tests using, say, a large cage with flowers and leaves instead of a simple Y-tube choice experiment.
But, of course, lots of work remains. Did the authors miss an orchid that the mantis really resembles? Does the mimicry protect the insect from predation in addition to helping it find prey? Are there other cues that attract insects besides the color and shape of the mantis? It is possible, after all, that the insect has evolved pheromones, or a scent, that also attracts pollinators. Remember that the case of orchids that mimic insects to get pollinated (the reverse situation; deceived bees try to copulate with bee-mimicking orchids and, in the process, get pollen stuck to their bodies), those orchids have evolved a scent that mimics bee pheromones.
Finally, the photos above show that far more than color is involved in this mimicry. The mantids have developed elaborate petal-like extensions to their legs and bodies, as well as special markings, that also mimic flowers. The authors tested only color resemblance, but clearly the mantid also mimics the shape of flowers. It’s likely that a pollinator will be attracted to the general vicinity of the mantid by its color (bees don’t see that well!), and then make a final decision to approach more closely based on shape. That would impose strong selection on the mantids to look more like flowers.
, , and Habitat selection in a deceptive predator: maximizing resource availability and signal efficacy. Behavioral Ecology, online, doi: 10.1093/beheco/aru179.