Pause for a moment to consider the insect equivalent of washing hands. It’s as time-consuming an affair for them as we humans find it to be, not least because they have six legs to deal with – and there’s no supply of water on tap. Yet it’s just as necessary . . .
. . . and so much more interesting.
Here’s a female hoverfly, the Many-tufted Sedgesitter (Platycheirus scutatus), gripping a blade of sedge grass with four legs while passing its pair of front legs across its compound eyes. This insect is perhaps 7mm long, and this action is likely to pass unnoticed by us without magnification.
A series of photographs of this insect taken in the Cemetery in May 2023 show her engaged in a comprehensive wash and brush-up dealing with head, eyes, abdomen and wings. At each stage, keeping two pairs of legs firmly grasping the sedge, the freed pair went to work on cleaning the nearest body part. If you ever wanted to see double-jointed behaviour in action, you’d have seen it then.
A different approach is taken by bees whose strong mandibles (something that flies and hoverflies don't possess) can be used to bite into a leaf so that they are suspended in mid-air. With no legs needed to secure a purchase, all six of their legs are then freed for a similar task. Here is a male Marsham’s Nomad Bee (Nomada marshamella) seen in the Cemetery in April 2025. There’s quite a bit of leg action happening here on the edge of a Bramble leaf: its left hind leg is being rubbed under its wings along the top of its abdomen, and he may be cleaning the underside of his thorax with the left foreleg.
These processes are not to be rushed. In both cases, I had perhaps 10 minutes to capture the action.
This cleaning business can also be undertaken in a standing position, as can be seen here with a female Tiger Hoverfly (Helophilus pendulus) that's rubbing her front legs together while perched on an Oxeye Daisy:
“People think flies are always dirty”, Dr Erica McAlister, Senior Curator for Diptera at the Natural History Museum, said to me when I showed her the first photograph on this page when we met at Knepp recently. “Yet nothing could be further from the truth”. The fastidious nature of flies may come as a surprise. If in doubt, ask yourself: does the Yellow Dung Fly below, seen in the Cemetery in May 2023, look dirty?
So what’s going on here?
This behaviour is simply “grooming”. It helps insects maintain a sharp sense of smell so that they can continue to find food, sense danger and locate a suitable mate. They are removing environmental pollutants and even chemicals that they themselves have produced. This cleans their sensory organs, especially the antennae, and removes attached pollen particles, pathogens and parasites. In some cases, as they gather particulates off their bodies, they ingest them so that they can be efficiently expelled later. Think of this as a kind of self-protection strategy. It happens pretty much incessantly, one more vital sign of a healthy environment.
Think of this next time you wash your hands . . . or feet . . .
Written and photographed by Rob Tomlinson