Beetling About with parasitic wasps

This month’s insect is a parasitic wasp called Echthromorpha intricatoria, but happily it also has a vernacular name, the Cream Spotted Ichneumonid (CSI). I caught it flying around the garden a few weeks ago.

Ichneumonids are wasps that parasitise other insects. This one attacks the pupae of large moths and butterflies and seems to prefer pupae ‘protected’ by hairy silky webbing.

Ichneumonid wasps get their name from the Greek word for ‘tracker’, as the females are constantly hunting in low vegetation for a host. Once a suitable host is found they stick their long ‘sting’, which is actually their egg-laying organ or ovipositor, into a caterpillar or pupa. This CSI specimen, about 2cm long, is clearly a female as it has a long ovipositor sticking out the tail end. 

Different types have different lengths of ovipositor because they attack different kinds of host. This one has quite a long ovipositor to get through the layers of the silk cocoon around a moth pupa and then penetrate the pupa to lay an egg.

There is a common pale-brown ichneumon in the Illawarra with a short ovipositor – it lays its eggs in smooth bodied caterpillars like cutworms – the ovipositor doesn’t have far to penetrate. Species with the longest ovipositors, often several body lengths, use them to drill through wood so that they can lay in wood-boring larvae.

The CSI lays eggs in pupae – that means its larva must develop rapidly as larvae are generally not long-lasting. These wasps lay particularly large eggs, in which the larva is well-developed. The eggs hatch in days and the larva inside the host sheds its skin to grow every 2 or 3 days. The larva basically kills its host immediately, so the host becomes a ‘lump of meat’ (as described by the British Museum expert), rather than being paralysed.

Other insect parasitoids often keep the host alive for as long as possible, as the host provides a protective shell. We call all these wasps (and similar flies) parasitOIDS, because they kill the host, unlike parasites, for example the fleas and lice on humans that just suck blood and thankfully don’t kill.

Echthromorpha intricatoria is a common species in our area.