Ants are one of the most abundant groups on earth, but, curiously, not a lot of things eat them. Yes, there are anteaters (who also eat a lot of termites), and some lizards specialize on ants, but the little critters are full of noxious chemicals and pheromones that put them way down on the list of predators’ preferred foodstuffs.
Because of this, many other insects and arthropods have evolved to mimic ants, taking advantage of the aversion of predators to anything antlike. These mimics are called myrmecomorphs, and they’re the subject of a really nice eponymous feature in this week’s Current Biology (access is free, too). The name comes from the Greek “myrmecos”, for ant, and “morph” for form. The authors are Florian Maderspacher, the journal’s senior reviews editor, and Marcus Stensmyr, a researcher at the Max Planck Institute for Chemical Ecology at Jena.
I won’t summarize the text, which talks about the history of work on these beasts; you should read that for yourself. But I do want to show some of the amazing photographs of ant mimics.
When a perfectly edible species evolves to resemble a noxious one that is avoided by predators, thereby gaining protection from being eaten, it’s called Batesian mimicry, after the English naturalist and explorer Henry Walter Bates, who described the phenomenon.
We’ve read a lot lately about the amazing shapes of treehoppers (membracids). Here are some photographs of the treehopper Cyphonia clavata, whose helmet (pronotum) has evolved to resemble an ant.
The picture below shows the hopper with a sympatric (living in the same place) noxious ant, Cephalotes atratus.
As the authors note:
Notably, the ant-mimicking structure seems to be inverted, with the imitated head facing towards the back of the treehopper. That way, as the treehopper moves forward, it probably creates a rather good impression of a reversing and agitated ant in erect defensive posture, deterring any would-be predators. To complete the illusion, the terminal segments of the treehopper’s hindlegs, coloured like the ‘ant’, most likely serve as the ‘ant’s’ forelegs, which provides the static protrusion with the illusion of movement. Too bad our specimen was dead.
Of course, for this mimicry to evolve (and work), the noxious ant “model” and its edible mimic have to live in the same area, and be encountered by the same potential predators.
Some mimics imitate the ants only during part of the life cycle. Here’s a nymph of the Texas bow-legged bug (a true bug), Hyalymenus tarsatus (left) imitating an ant of the genus Ectatomma (right).
Some of the most remarkable cases of ant mimicry involve spiders. To pull off the trick, the spiders have to make their extra pair of legs look like antennae, put a constriction in their cephalothorax to resemble the separate head and thorax of ants, thin out their body, and, often, evolve fake eyespots to look like the large eyes of ants. Here’s a spider Sphecotypus niger (left) looking like the ant Pachychondela villosa (right), which the authors describe as a an “aggressive and predatory ant.” Note how the spider extends its first pair of legs forward to look like antennae:
There are several types of ant mimicry. Besides Batesian mimicry, we have “aggressive mimicry,” in which an animal will evolve to resemble another animal so that it can deceive it into thinking it’s one of its fellows, who then unwittingly allows it to approach. (There are other types of aggressive mimicry as well: some mantids imitate orchids, hanging from trees and waiting to eat the hapless insects who come to pollinate it.)
Here’s a remarkable case of aggressive ant mimicy. The animal on the left is actually the crab spider Aphantochilus rogersi, which resembles ants of the genus Cephalotes (right). It’s hard to tell them apart! The spider’s head is biting the ant’s neck, so the ant’s head is bent down. It’s a goner.
This type of mimicry implies that the “model” ants must have pretty good vision, for otherwise there would be no selection on the spider to resemble an ant so closely. And indeed, ants of this group do see pretty well: you can see that its eyes are quite large. From this you’d predict that mymecomorphs who prey on ants that don’t see very well might be less perfect mimics.
I love cases of mimicry, for they truly show the power of natural selection. The degree to which mimics resemble models—and it’s often spot-on—shows that there is lots of genetic variation in the model that can be used by natural selection, and that the selection is strong enough to affect many features of the mimic. It’s one of the few cases—sex ratio is another—in which biologists know a priori what the optimum result of selection should be, and how closely selection can achieve that target. As you see from the photos above, it comes damn close!
The power of selection acting on pervasive genetic variation is, of course, also responsible for the power of artificial selection, something that Darwin highlighted in The Origin:
“Breeders frequently speak of an animal’s organization as something plastic, which they can model almost as they please.”
I won’t use the word “spiritual” to describe my feelings when I see the remarkable forms that have resulted from blind, materialistic processes acting on DNA molecules, but they certainly evoke considerable wonder.
Ug. The levels and color are better in the original photos. For example:
http://www.alexanderwild.com/Insects/Amazing-Arachnids/10458708_suYQ6#1175873810_7MrGx
Bootiful! You should put up an item about how you get those images. Very nice indeed.
Thanks!
I’m not sure I can condense all the relevant technical bits into an “item”. I am writing a how-to book on bug photography, though.
I will buy that!
Dominic– go check his recent blog post:
http://myrmecos.net/2011/05/10/processing-a-field-guide-photo/
Amazing! I’m now totally addicted to Alex’s site– simply beautiful macro photos!
It’s been in my bookmarks for some time. Long-time lurker…
Wow…!
erm…wow indeed. this is fucking amazing.
Ooh, watch out now Dr Coyne, you may become Templeton’s next recruit.
When I was a grad student, I worked on another case of ontogenetic mimicry.
In French Polynesia, there is a species of surgeonfish that is a rather drab brown color as an adult, but a vivid yellow as a juvenile.
Turns out the juvenile, while it is of a certain size range, will mimic a species of bright yellow angelfish perfectly; right down to even holding its fins differently, and having slight discolorations where the angelfish’s opercular spine is.
The angelfishes live in small groups of 5-8 individuals in shallow water, which is also where the surgeonfish juveniles have their preferred food.
It was pretty clear that the surgeonfish were doing this in order to gain some reduction of predation pressure via grouping behavior, since as adults they tend to live solitary.
As soon as the surgeonfish grew slightly larger than the angelfish, they would leave the group, start using more shelter, and migrate into deeper water. There, they would lose the yellow coloration over a few weeks, and start looking like the adult surgeonfish.
I worked on ontogenetic color change in fishes, and I rather liked that this was a slightly different example of why some species do this.
A few wks ago a few carpenter ants got inside my place via some firewood. I don’t get too worried since without water they don’t last that long, but I was really surprised to happen on one getting attacked by a little spider living among a few orchids that I have, especially since it was about 1/4 the size of the ant. I didn’t think a spider would go after an ant, but by the time I saw them, the ant was pretty well encased in webbing but still alive. The little ant would periodically twitch the ant to see if it was still dangerous, and then sometimes add to the entanglement. If the ant was edible, that little spider ate well for a long time!
Per the current biology piece:
There is chemical mimicry as well as morphological, and mimicry of the chemical sort has evolved among some myrmecophiles that do not resemble ants at all in their morphology. Among those are the larvae of some lycaenid butterflies or blues, and there is an absolutely fabulous video narrated by Attenborough showing how larvae of the European alcon blue butterfly, Phengaris alcon, are taken into the nests of ants, where they mimic not only the pheromones of ant larvae but also the sounds of hungry ant larvae and are thus nourished and protected by the ants. They complete their life cycle in the nest of the ants, except when they are parasitized by Ichneumon eumerus, which has evolved a chemical defense that results in almost total pandemonium among the ants, which are thereby prevented from preventing Ichneumon eumerus from parasitising the mature larva of the alcon blue.
The hosts of a substantial portion of the Nearctic species of Ichneumon are unknown, but it seems possible that one or two might have habits analogous to those of Ichneumon eumerus.
Ugh. I was absent-mindedly prevented from preventing the “prevented from preventing.”
It’s the Red Queen in action!
🙂
I doubt anyone knows, but I would bet this wasp was parasitizing that butterfly long before it started taking advantage of ants as nursemaids.
That would be my hunch, too. Reading here about myrmecophily in lycaneids, some kinds are merely mymecoxenous (ant-associated).
If we find a mimic and model who are not syntopic, we would probably think they were syntopic at one time, and try to find out what has caused them to change their ranges or habitats such that they are no longer syntopic.
Also interesting is within species mimicry, where, for example, a “sneaky male” looks and acts like a juvenile or female. These males, also called “supermales” because of large testes, are able to participate in spawning events (fish talk) without rousing the ire of the more common normal males.
Actually, I seem to remember the case of a coral snake mimic that looks like a coral snake but isn’t poisonous—but lives in the tropics outside the range of the putative model. The explanation was a migratory bird that would “learn” in the breeding grounds and “practice” where it overwintered.
Wow! That’s so cool!
Me too!!! Thanks for this link!
Another neat thing, when it comes to the hugely successful arthropoda, is that you don’t have to just read about this stuff in science mags…You can find a lot of it right in your own backyard! Spiders that look like ants, flies that look like bees, flies that look like spiders, spiders that look like flowers…
Did I mention this stuff was so cool?
(This post’s surpassing eloquence dedicated to my long ago prof at Cornell who was teaching plate tectonics to us when he turned to the class (from the board), spread his hands, and intoned, “This is just SO cool!” I’ve never forgotten that moment.)
Isn’t God amazing?