Bird-muck mimicry

Posted by Graeme Lyons , Friday 2 July 2010 16:39

I found this Lime-speck Pug moth on the wall at home and it got me thinking about bird poo. Looking like something unpalatable is a great way to avoid being eaten and imitating a bird poo is a very popular tactic among invertebrates. There are many micros, particularly tortricoids, as well as a few smaller macros that do this. There are also quite a few beetles, including the weevil I featured in a previous blog, Platystomos albinus. There are even a trio of tiny longhorn beetles that do the same thing. Perhaps the most convincing one of all is the Chinese Character moth. A right little bird turd of a moth if I ever did see one. Some caterpillars do it too. There must be many more species that do this too that I have not encountered. The Alder Moth starts of looking like a dropping but when it becomes too big, it changes and looks completely different. They even curl up to form the shape of a dropping! There is something interesting happening hear, clearly the size of the insect dictates whether being a bird-dropping mimic is beneficial. There is a limit to the size of droppings, large birds such as Herring Gulls just produce buckets of white wash, wildfowl defecate in or near water, pigeons might be a part of this but it seems that it is most likely passerines' droppings that the insects are emulating. The fact that some insects change their strategy when they become too big shows how beneficial this strategy must be, if it did not work they would not start off in this form. Fascinating stuff, I love how dozens of invertebrate species have been shaped by little black and white sticky turds. Fast forward a few million years and the Buff-tip may have evolved to look like a cigarette-end!

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