Dec 9, 2021
Unravelling the flea beetle masquerade
Hiding in plain sight is generally not the wisest life choice for insects, given the number of other animals that generally want to eat them. But adaptations to blend in with your surroundings can make it a strategy worth pursuing.
Take flea beetles. These notoriously hard-to-control pests have evolved what initially seems like an extremely odd, but actually perfectly logical camouflage. In many cases, they look like the damage they do to plants when they’re feeding on them. The idea being, as ever with visual trickery, to deceive predators, or at least those that hunt by sight. ‘Have your cake and eat it’ or ‘you are what you eat’ — pick your cliché for this approach to undisturbed pestilence.
What’s been unclear up to this point is what was driving the evolutionary deception: The type of plant, with its unique type of feeding damage being suited to hiding certain beetles, or the physical characteristics of the beetles themselves, with them evolving feeding approaches that provide them with a bespoke masquerade.
Modelling the masque
Luckily, a team of Spain-based researchers were prepared to try and find out. Using a dataset of French species, they built a rather complex statistical model going deep into the relationships between plants and beetles, colours and sizes — the specifics of which we definitely won’t be delving into here.
What they found was that the masquerade can be partially explained by both of the hypotheses. However, the dominant evolutionary mechanism appears to be the idea that it’s insect-driven, with, ultimately, those visual predators the driving force behind improved strategies to match leaf damage to flea beetle body size and colour.
Furthering the point, they note that there are limits on how deep the smallest flea beetles can penetrate into leaves, meaning that lighter colours are better suited to these small body types, while large species, munching holes right through the leaf tissue, would make it a lot more sensible for them to be dark. And, in general, they are.
A case not quite closed
Slightly muddying the waters of the argument that predators such as birds have pushed flea beetle characteristics along by not eating the ones they couldn’t see; the researchers acknowledge that there’s actually no data recorded to date which suggests that their search efforts suffer faced with this kind of deception. Those of humans do, though, apparently, when faced with computer simulations of leaf holes and beetles, so it seems there’s something in it.
It always deserves reiterating what both ecology and evolution are pretty damn complex in their mechanisms, so the combination of the two represents quite another level of intricacy. The research only looked at France, so who’s to say whether the conclusions hold for the rest of the world. There are also other evolutionary drivers left unexplored.
This one might have more to run, but for insects that can’t run very fast, it’s pretty clear that becoming the double of your just-eaten dinner must convey some advantages.
