Instead of presenting our own readers’ photographs, I wanted today to highlight a post by naturalist/evolutionist/photographer Piotr Naskrecki from his wonderful website The Smaller Majority. I doubt that Piotr reads my site, so he probably doesn’t qualify as a “reader,” but I do know him and have permission to reproduce his photos. That’s good enough for me, for today’s post, in which I shamelessly steal his photos and descriptions, will stun you with yet another achievement of natural selection.
In fact, the species at hand, the ghost mantis Phyloocrania paradoxa, is a fantastic example of crypsis (camouflage). The resemblance of this species to a leaf is simply amazing—involving shape, color, and behavior. As Wikipedia notes:
Phyllocrania paradoxa is camouflaged so as to appear as dead, dried-up leaf material. It has an elongated head, a flattened, extended prothorax (together referred to as its “elaborate headdress and shoulder shields” by one enthusiast), and leaf-like protrusions from its limbs. The mantis also has a forewing that looks like a desiccated leaf, and the “creases” in the wings are actually shadings of pigment.
Wikipedia says that the genus Phyloocrania contains three species, but Naskrecki says that they’ve all been “synonymized” (lumped into a single species). The confusion comes because there’s tremendous polymorphism (variation among individuals) in both shape and color, so dividing individuals up into species, particularly for populations living in different places, is tricky at best. And the reason for this variation, which I’ll discuss in a second, is unclear.
The best photos and description can be seen at Piotr’s new post, “Ghost hunting.” First, a photo (all captions are by Piotr, and photos are copyrighted). Look at this thing! Can you even tell front from back?
After first learning about this remarkable creature, Piotr went to Zimbabwe, with the mantis high on his bucket list. He had trouble finding one but finally succeeded:
The ghost mantis was one of my most desired quarries and I started looking for it the moment I landed. Alas, a month on and with no trace of the animal, it was beginning to feel as if I were really hunting a ghost. I had spent countless hours sifting through the leaf litter, scanning bushes and trees, sweeping my net through all kinds of vegetation – nothing.
One day I stood on the platform of a railway station, waiting for a train to take me to Bulawayo. It was late October, the peak of the dry season, and shriveled leaves were falling from trees onto my head in a rare, merciful breeze. One, fairly large and twisted brown leaf landed on my shoulder. I tried to brush it off but it just sat there, trembling in the wind. I flicked it again. It landed lower on my sleeve. And then the leaf started to climb up my arm. I looked, still not believing. Could it be? No, this is just a piece of withered plant. But it was, finally, a ghost mantis.
They come in a variety of colors, with the color changing at each molt. Here are two different-colored specimens (note the differences in shape as well):
It took Naskrecki 25 years before he saw another one of these, this time in Mozambique’s Gorongosa National Park, where he’s been spending a lot of time. He notes that ghost mantids are widely available to collectors:
Thanks to their otherworldly appearance ghost mantids have long been the favorite of amateur insect collectors and, since they can be easily bred in captivity, they have recently become very popular in the pet trade. Now all you need to do to see a live ghost mantis is to pay a few bucks online and one will be delivered to your door. But for an animal so widely kept, shockingly little is known about its biology and behavior in its natural habitat.
The polymorphism for color, which appears to rest on changes at each molt, immediately raised a question for Matthew and me. If the color makes the mantid cryptic on leaves, and the color must match the leaves, how does the mantid know what color it is? It must have a way of matching its color to its background, so it has to know what color it is. Can it see itself, or does it have some endogenous way, not involving self-inspection, to “know” what color it is and choose an appropriate background? Or does it even go to the appropriate background? (After all, perhaps you can be a brown mantid on a green tree and still enjoy some protection from predators.)
It is probably to the mantis’s advantage to change color with molts. That way, as Naskrecki suggests in the photo caption above, the predator has a harder time learning to pick you out from the environment, as it has to learn various colors. (This form of selection, in which the rarer types are favored because it’s harder for the predator to learn their color or pattern, is called “negative frequency-dependent selection”.) Or perhaps not—if the predator hunts by shape alone.
And why is shape so variable? (There’s an example of this in the third photograph below.) Such variation among individuals in morphology is remarkable in insects; I know of no other species in which individuals differ from each other so strikingly. That, too, could be an adaptation: a developmental program that is sufficiently plastic to allow the cuticles of different individuals to develop in different ways. (I find this less likely than variation in color.) But there’s a constraint: they still must always resemble leaves. How much variation is there among individuals? And do individuals change their “ornamentation” with each molt?
I’ve raised many questions here, but none have answers. The question of whether an individual can choose a matching background should be easily answerable in the lab: just put individuals in cages where they have a choice of vegetation. So far as I know, that hasn’t been done, but even a hobbyist could do that, and get a scientific paper!
An alternative hypothesis: if an individual molts on a certain vegetation, perhaps its developmental program will channel its color into that of the background vegetation. If the mantis tends to stay put on that vegetation, it need not be forced to “choose” a background that matches its color. I’ve described an example of such developmental polymorphism in an earlier post on the moth caterpillar Nemoria arizonaria, so it’s possible that this also occurs with the mantid. But that presumes that mantids stay put. And we don’t know whether they do.
Finally, if they’re so bloody cryptic, how does a male find a female when it’s mating time? Piotr suggests that they use pheromones. That’s a reasonable hypothesis, but again, we just don’t know. There’s a lot of interesting work to be done on this species!
Here’s a female ghost mantis with a newly-laid ootheca (egg case): the white structure behind it:
There’s more information (and more photographs) at Piotr’s site, so go over and have a look (be sure to see the photo of a mantis molting). We’ll end with two more of Piotr’s lovely photos:
This photo shows the variation in both color and morphology.
Now you surely want to see some videos, and, because this species is commercially available, there are many on YouTube. I’ll show three.
As Piotr says, this species is an “ambush predator”: individuals wait until some hapless insect walks or flies within range, and then quickly strike. Here’s a video of a captive mantis taking down a waxworm (at 45 sec. in; note the speed of the strike and how the mantis holds its front legs up by its head):
Here’s a brown female being handled:
And here’s a green morph:
Note that Naskrecki also has a photo-and-science book with the same name as his website, a book that got great reviews as well as a rare starred review from Publishers Weekly. It was published in 2007 by Harvard University Press, and would make a nice present for lovers of nature photography and biology.
Finally, I’d love to have one of these mantids (I won’t, though, as it’s a bit of trouble and I travel a lot), and since they’re bred in captivity that doesn’t endanger the wild populations. There are many places to buy them (one is here), but be sure you learn how to take care of them properly (go here).
h/t: Matthew Cobb