Reader Lou Jost, who lives and works in Ecuador, found a really cool beetle, and a case of possible mimicry that I didn’t know about. His descriptions are indented:
Here’s another weird insect I found. This one is a translucent chrysomelid beetle larva, subfamily Cassidinae, which builds a rough likeness of another insect or spider, by carefully placing bricks of poop onto its back with its “anal turret” (that’s a real term!!). It does this by touch since it can’t see what it’s doing back there. When this creature grows up it turns into a partly-transparent beetle that also has a fake insect on its back, a fly, but this time it is just done with pigment.
JAC: The adult, with spider-like markings on its back:
The adult also has amazing feet. They are like wet mops and can stick to glass and other surfaces, and withstand enormous forces (60-100 times their own weight). The liquid is a viscous lipid. The feet are marvelous under a microscope. I think the claws might be used as levers to get the wet, flattened, divided hairs to unstick from the surface.
I must have taken many thousands of images of this thing during its life. The foot pictures shown here required about 700 pictures each. You can see the microscopic droplets of lipids on the flattened hair tips. There are more photos and info here.
Marvelous! I agree that the larva is up to something, and it does look like a spider mimic in poop.
I don’t get the spider mimic in the adult, but it too looks like it is trying to fool us. Maybe its trying to look like a hole in a leaf?
Mark, that was a slip of the pen. The adult is a very accurate mimic of a fast fly, facing backwards on the beetle’s back. These flies are too wary and quick for most things to catch, so I imagine not many things would try.
Doh! My senility is slowly creeping up on me.
Amazing photos of the feet!
Those were fascinating, with drops of lipids visible on the ends of the flattened hairs forming the pads on either side of the claws. After the insect died I took way too many stacks of pictures of them. Never quite got it perfectly right. I’ll probably take a few thousand more to get it right, though maybe the liquid has dried up by now. Check out the link at the end of the post for some more photos.
What a lovely little foot! I also like how beetles look like they are jammed into some sort of wrapping when viewed from beneath.
Just amazing. What an odd and marvelous creature.
These are fantastic, Lou. Maybe Ecuador would be a great destination for PCC(E) this summer….
I think so too! He’d have a free Amazonian guide.
Try putting a bug in his ear. 🙂
A bug that uses mimicry to look like a human ear.
Haha, yes!
Can you feel any of those tremors where you’re located, far up in the mountains?
Yes, a few nights ago my house shook gently with wide amplitude vibrations for 30-40 seconds, and then it happened several times afterwards that evening, though weaker. I knew that meant “big earthquake somewhere far”, and it was a 6.2 aftershock on the coast. This is causing more destruction and making rescues and debris-clearing impossible.
What a fine example of tropical adaptation. The putative — but I buy it — fake fly pattern on the back of the adult beetle is truly impressive. The beetle antennae even seem to mark out a false wing outline. The sleek, big-eyed flies seemingly represented in the black pattern are wary and evasive and probably difficult for most birds to catch. I suspect that young birds soon learn such flies are a waste of time to attack and afterwards ignore them. Being mistaken for the fly and ignored would also be good deal for the beetle.
Some butterflies seem to take their evasive skills to the point of mockery. When a predator (or an observer) approaches, they fan their wings, and this apparently (I speculate) serves to advise (signal) the predator that it has been detected and no longer has the advantage of surprise. A prey’s drawing attention to itself through conspicuous movement would be inexplicable were the action not in some way helpful to it.
I think many overestimate the repulsiveness of small spiders and underestimate the ability of experienced birds to distinguish imperfect mimics. Many tropical birds eat small spiders just as eagerly as they do beetles and grasshoppers. Even if spiders were to repel small birds, it seems unlikely that many birds, viewing from a few inches away, would be fooled by this crude spider imitation. It is more likely to my mind that the crud on the back of the beetle larva is made to look like (“made to” in the teleonomic sense of being pressured by natural selection) dried parts of small flowers that become stuck to rainforest leaves and branches. This could be tested in part by tethering real spiders (and known edible prey as controls) to leaves in the forest (or greenhouse aviary) and recording (with motion detecting photographic traps) how birds (and other potential predators) respond to them.
Enjoyed the read.
Thanks for those thoughts. That’s a good point about spiders. The “legs” were the main reason I thought the fecal shield imitates a spider or generic insect. They don’t seem like they are imitating random debris. Also, though you can’t easily tell from the photo, these larvae hang out mostly on the undersides of the leaves, where debris does not accumulate. You are right that most birds would not be deterred by spiders, but perhaps smaller predators would be. Small wasps, for instance, are important visual predators of small insects, and some might be deterred by this. But I don’t really know. I wish I had the time to do the kinds of experiments you propose!
Insightful and helpful comment. Thanks.
Wonderful photos, Lou!
What a beautiful beetle. Those feet are simply incredible. Thanks for sharing.
My pleasure! Thanks for looking.