Parasitic wasps

Parasitic wasps, such as the ichneumon wasp pictured here, have a life cycle that sounds horrific at first hearing, but they actually perform a great service to mankind by focusing their attention on species that we normally regard as pests for the damage they do to crops.

Parasitic wasps breed by laying their eggs inside other small creatures, such as spiders, aphids, caterpillars or other species of wasp. This is done by injecting the eggs through an ovipositor, or egg-laying tube.

When the eggs hatch, the larvae eat their way out of the host’s body, resulting in the death of the latter. As many as 3000 wasp eggs can be laid inside a host.

Some very small species of parasitic wasp lay their eggs inside the eggs of other species. The introduced eggs then divide many times before hatching, such that as many 150 wasps (all clones of each other) can emerge from a single host egg.

However, parasitic wasps do not always have things their own way. One species of parasite can become the host for a different species, and this can happen several times over in a process known as hyperparasitism.

The smallest known insect, the fairy fly, is a parasitic wasp that infects insect eggs. The fairy fly is only 0.2 millimetres long.

© John Welford