Sheep in Wolf’s Clothing

Insects that are armed with powerful stings are often strikingly coloured to warn off potential predators – a strategy known as aposematism . A good example of this is the black and yellow colour pattern of the European wasp (Vespula germanica).

Some harmless insects take on the appearance of aposematic insects even though they are not actually dangerous themselves. Hover flies are an example of this. One common hover fly species – the drone fly Eristalis tenax – is an excellent bee mimic, and was the star in a recent ‘one minute bugs’ video (link).

Other common hover flies (image below) are harmless flower visitors but their striking yellow and black markings superficially resemble the markings of bees or wasps. Bees and wasps usually have stings and consequently are left alone by many predators. Hover flies don’t have stings, so by adopting colour patterns similar to bees and wasps this affords the hover flies some protection. This defence strategy is known as Batesian mimicry.

Now for a wee bit of history. H.W. Bates (hence ‘Batesian’) was the first scientist to conduct a major study on mimicry – in the Amazon Basin in the 1860s. Charles Darwin recognised Bates’s work on mimicry as critically important to the theory of evolution, and cited it extensively in later editions of his own great work The Origin of Species. Darwin appears to be quite a fan, because in a letter to Bates in 1862 Darwin wrote:

“Dear Bates. I have just finished, after several reads, your paper. In my opinion it is one of the most remarkable and admirable papers I have ever read in my life.  .  . Your paper is too good to be largely appreciated by the mob of naturalists without souls; but, rely on it, that it will have lasting value, and I cordially congratulate you on your first great work.”

I am particularly intrigued by insects which mimic other insects that would normally appear very different from their own body shape. It’s easy to see how a yellow and black patterned fly could look like a bee or a wasp (e.g. the hover fly), but how about a beetle which looks like a spider-hunting wasp? The yellow-horned clerid beetle Trogodendron fasciculatus (Cleridae) – image below – mimics the spider-hunting wasp Fabriogenia sp. (Pompilidae) – lower image.

If you place them side-by-side you might think the resemblance is only superficial – dark bodies and yellow/orange antennae. It’s when they move that you see mimicry at its best. Spider-hunting wasps move in a characteristically jerking manner and flick their antennae constantly as they look for spiders. The yellow-horned clerid beetle mimics these movements exactly, so much so that when you see one moving you would swear that it is a wasp. The beetle would then be completely safe from predators especially spiders. No sane spider would want to go near an insect that appears to be a spider-hunting wasp!