The house fly, Musca domestica, is perhaps the most widely distributed animal that lives alongside people. Where we cook, eat and leave things lying about, it follows. It is about seven millimetres long, grey-black, with four dark stripes running down its thorax and a pair of large, rust-coloured compound eyes that wrap almost all the way around its head.

It tastes with its feet. Chemoreceptors on the tarsi detect sugars the moment it steps on them; the fly stops, lowers its proboscis and dabs at the surface with the spongy pads at its tip, pumping up whatever it can dissolve. When the patch runs out it does not leave straight away, but walks in tight loops nearby, searching for more.

Why you cannot catch it

A fly sees an approaching hand as a looming shape, and it judges how soon that shape will arrive. When the time to contact falls below a fraction of a second, it plans a jump away from the threat, raises its wings and is airborne in well under a tenth of a second. Move slowly and you can get surprisingly close. Move quickly and it is gone before your hand arrives.

It is also stubborn. Chase it off something it likes and it will circle the room for a few seconds, then come straight back to the same spot. Each time it is disturbed it becomes a little more jumpy, and a little more inclined to buzz past your face on the way round.

Housekeeping

Between meals it grooms constantly: front legs rubbed together, then swept over the eyes and head; hind legs scissored against each other, then stroked over the wings. Flies spend a remarkable fraction of their lives cleaning themselves, mostly to keep their sensory hairs working.

Leave your hand still for a while and it may decide that your hand is the most interesting thing on the table. Click or tap near it, or wave the cursor at it, to shoo it away. It will be back.