The Lacewing fly is an interesting predator

THE OTHER night I was checking the patio lights to see what species of moths had been drawn to them.

But the first thing I found was an interesting insect that wasn’t a moth.

It had a pale green body with black markings, a bit over a centimetre long, and four very large wings folded over its body like a tent. The wings were transparent, iridescent and quite heavily veined. The whole insect had a rather fragile appearance.

This was the common green lacewing fly which is largely nocturnal and is attracted to lights in the same way that moths are. Before hibernation their body colour changes from green to pink.

During the summer you may spot lacewing eggs on leaves, or sometimes on wooden surfaces. They are clearly visible to the naked eye and impossible to mistake for anything else because each little oval egg sits on the end of a stalk. The whole thing looks rather like a pin with a large head.

I was delighted with my discovery because lacewing flies are very useful things to have around the place. Their larvae are fierce predators that specialise in attacking the creatures that do most damage in the garden, greenhouse or conservatory.

These larvae are sometimes called “aphid lions” and, as well as preying on aphid species like greenfly, whitefly and blackfly, they kill spider mites, thrips, mealy bugs, leaf hoppers and the eggs and caterpillars of some small moth species that can become garden pests.

They deal with their prey by catching it in their large jaws and injecting a paralysing venom into it. The jaws are hollow and are then used to suck all the body fluids out of the prey.

Aphid lions have voracious appetites and, although they only remain in the larval stage for two or three weeks, each individual will kill around a thousand pests during this period.

Lacewing flies undergo a full four-stage metamorphosis —- in other words, egg, larva, pupa and winged adult. The adults, like the one I found on the patio, have very different personalities to the killer larvae. They are delicate creatures and in most species completely vegetarian. They live on a light diet of pollen, nectar and honey-dew.

When the females have enough of this food they are stimulated to mate and lay 200-250 of those peculiar matchstick eggs. These hatch into the aphid lions which will pupate by spinning a cocoon from a silken thread that they extrude. About five days later the pupae hatch into adult lacewings and the cycle is complete.

Lacewings flies are so beneficial to humanity that in some countries there are commercial breeders who sell them to farmers, gardeners and horticulturalists. As far as I know lacewing flies are not available commercially in this country. Luckily the native wild ones are fairly common.

They like plenty of trees and shrubs and they seem to thrive around water. The adults also need a supply of pollen and nectar if they’re to breed. Biological controls are the way of the future.

[e-mail]