INSECT INSIGHTS

by Dave Walker

This month - green lacewings, the 'delicate destroyers'

Like most amateur microscopists and naturalists no doubt, I always keep an eye open for something interesting to study under the microscope, either the stereo or compound. The other day while on a walk I found a dead green lacewing in good condition, so popped it in the empty 35mm film cassette I usually carry for the odd things I find and brought it back for a closer look.

Lacewings are one of my favourite insects, they have large intricately veined wings and the green lacewing shown above and left has beautiful copper coloured eyes when they catch the light.

The image at the article head doesn't really capture the majesty of the insect, as the body and antenna have dried and curled up. (I shouldn't have left the insect overnight before photographing). In life the antenna are long, straight and delicate.

One of the first things I noticed when starting to study the insect was a rather bad smell. I later learnt that lacewings release noxious smelling fluids when threatened (and is sometimes called the stinkfly), so this fluid albeit in the dead insect was the probable cause.

The image right shows one pair of front and hind wings and highlights the wonderful veining and just a hint of their delicate translucency. The top wing is 22mm long.

The image right shows part of one antenna of the lacewing viewed under a 3.5X objective and incident lighting. Note the two different types of hairs. The antenna is ca. 0.2mm wide.

The image left shows part of one of the lacewing legs. The delicate green of the lacewing is also seen in the legs. Image taken using a 3.5X objective and incident lighting.

I sub-titled this article 'green lacewings, the delicate destroyers', as their appearance belies some of their habits. Here's a few intriguing aspects about them.

• Lacewings are insects in the Order Neuroptera (meaning nerve winged) and the green lacewings are in the family Chrysopidae. There are twelve species of green lacewings in Britain and they are widely distributed in the world.
• Although they have magnificent wings (which are held like an arched roof above the body when at rest), they are weak fliers and are often attracted to lighted windows at night.
• The adults and larvae are voracious feeders on aphids and therefore are a gardener's friend. To feed, the adults have biting jaws whereas the larvae have piercing and sucking mouthparts.
• The adult lays the eggs singly on stalks so that the aphids which hatch first don't eat the remaining eggs.
• The larvae often camouflage themselves from their prey with the empty skins of their victims (or other debris), which they flick on to their back with their jaws. The skin or debris is held on by the bristles .... crafty eh!
• .... but this isn't all, the larvae also like to eat the aphids often 'herded' by some ants. To avoid attack by the ants, the lacewing larvae will camouflage themselves with the fluffy wax that covers these aphids.
• After two weeks of gorging itself on aphids, the larva spins a silken cocoon typically on the underside of a leaf. It remains in this pupal case for a further two weeks or so before hatching to the adult .... which makes a further assault on the hapless aphids!

This chance find provided an enjoyable few hours of study under the microscope.

So when you're out on a walk or in the garden, especially at this time of year (mid-summer at the time of writing), when many insects are breeding and then dying, keep an eye out for interesting specimens .... even the humblest insect can provide a fascinating few hours of study and background reading.

Comments to Dave Walker welcomed.

References and further reading

1. 'Natural History of the Garden' by M. Chinery, Collins (Fontana) 1977. A wonderful book if you haven't come across it, well written and beautifully illustrated and covers most fauna and flora commonly found in a garden - from brambles to 'bugs' and birds!

2. 'Collins Guide to the Insects of Britain and Western Europe' by M. Chinery, 1986. Arguably one of the best single guides to a selection of the insects most commonly found in the area covered.

3. Encyclopaedia Britannica, 15th edition 1993. Most large encyclopaedias should have a good section on the insect Order Neuroptera and possibly lacewings.

Tip on photographing wings

While preparing this article I was disappointed with the images I captured of the wings using my usual cheap and cheerful technique of laying the insect parts on black card and photographing with strong sidelighting. The texture of the card although very subtle was as prominent as the wings and distracting i.e. see the image right.

So for the image earlier in the article, I put the wings on the lid of a glass petri dish and put the black card underneath. This put the card out of focus, but a benefit I hadn't anticipated, is that the strong low sidelighting was now to some extent coming from below and providing a sort of darkfield effect which emphasised the translucency of the wings.

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First published in August 1998 Micscape Magazine.

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