A chemistry master at school was universally known by the nickname Cleg, at least when he was out of earshot.

When quizzed, older pupils revealed that a Cleg, Haematopota pluvialis, is a particularly nasty form of fly that you do not notice until pain alerts you to the fact it has cut a hole in your skin and started to suck your blood.

It is very similar to a horsefly, except smaller, silent and stealthy, so normally not detected until the damage is being done.

At the time it seemed a rather apt name for an unpopular master, never happier than when wielding a cane, but was completely forgotten about until last summer’s heatwave.

The wet spring benefited the overwintering larvae and the hot summer was ideal for the adults. Bites were frequent, painful and itchy for days.

But all those years ago the boys had got it wrong – it is only the females that bite and suck your blood to provide the nourishment for the eggs they are about to lay. The males lack the sharp mouthparts to cut through your skin and are harmless nectar eaters and beneficial pollinators.

It is too early to say whether last year’s unwelcome population surge will be repeated; the larvae do not emerge as adults until May.