The imperfectly perfect impersonator

Insects face many struggles to survive: finding food and shelter, enduring bad weather, avoiding diseases. And, of course, doing their best to not become a meal for one of the many predators lurking out there.  In today’s blog, Athayde Tonhasca looks at impersonation as a survival strategy.

Some insects escape predation by camouflage, the ability to blend in with the surroundings and not be seen. Others fool predators into thinking they are part of the landscape by looking like leaves, twigs or other structures. This evolutionary adaptation is known as mimicry: stick insects are good examples of species that rely on this trick.

Some insects rely on a different ruse: they evolved to look like dangerous creatures, an adaptation known as Batesian mimicry (first described by the English explorer-naturalist Henry Walter Bates). By resembling a species that is harmful, being poisonous or aggressive, the non-harmful insect is less likely to be attacked by a predator.

The hoverfly Criorhina floccosa is a good example of a Batesian mimic; by resembling the common carder bumblebee (Bombus pascuorum), the fly can go about its business in peace, as predators will not risk being stung by what looks like a bee.

This hoverfly can be seen in Scottish woodlands, basking on sunlit foliage and feeding on hawthorn, rowan, brambles and rose flowers. Just like the hoverfly in the photo, these flies often forage along bumblebees. The larvae develop in decaying wood of mature broadleaved trees such as oak and beech.

The Hoverfly

The hoverfly Criorhina floccosa ©Athayde Tonhasca

The common carder bumblebee Bombus pascuorum ©Creative Commons

The common carder bumblebee Bombus pascuorum ©Creative Commons

You might say that it can’t be difficult for a bird or other predator to tell both species apart; the hoverfly is clearly different from the bumblebee. However, Swedish biologists have evidence to suggest that predators rely on rudimentary signs to identify their prey, such as colours, patterns or shapes. If an insect is able to mimic the few factors a predator has an eye for to distinguish between edible and inedible prey, the deception is effective; there is no need for a perfect match. This would explain why there are so many cases of crude mimicry in nature: there is no evolutionary incentive for a better disguise.

Hoverflies are some of the most frequent flower visitors in a range of habitat types. Although they do not receive the same attention as bees, hoverflies are becoming increasingly recognised as important pollinators for some crops, and especially for wild plants in higher altitudes and latitudes.