In the insect world, combinations of black and yellow and red and black serve as warning colours to would be predators.

It tells them that the insects are either inedible, toxic or sting and once sampled, birds and perhaps mice leave well alone in future.

One of many examples is the hooped black and yellow burnet moth caterpillar familiar in groups feeding on ragwort which is rich in alkaloid poisons that are then passed on through the pupal stage to the black and red moth.

Having said that, evolution has perfected a clever little trick of creating lookalike but harmless insects that mimic the toxic species and gain protection from that similarity.

One of the most familiar of the mimics is the little hoverfly of which there are many species, all resembling small wasps and therefore untouchable as far as most predators are concerned.

Hoverfly populations build up as summer progresses and our gardens play host to them on sunny days poised motionless in dappled shade. They are great migrants and swarms of them arrive in Britain every summer, the species illustrated being the most numerous.

Some years ago I stayed at a clifftop hotel on the south coast. All day and throughout the night countless millions of hoverflies sped in from the sea, up the cliff face and over the hotel heading inland, although many flew in through the windows. The migration lasted for my entire ten day stay without a break.

Hoverflies are harmless and great friends of the gardener as their larvae feed voraciously on aphids and greenfly.