Killer unmasked ....

A couple of weeks ago I posted some pictures of a drinker moth caterpillar, together with the larvae and pupae of the parasitic insect that killed it. The killer has emerged from the pupae and it looks like a tachinid fly of some kind.

You can see the prominent calypters at the base of the wings, which are a tachinid characteristic.

This individual has just emerged from its pupa and its wings have yet to expand.

A nasty way to go ....

A few days ago my youngest son and his partner called to say he'd found a drinker moth caterpillar but by the time I went to collect it the caterpillar had stopped feeding and become very lethargic - usually a sign that there were internal parasites gnawing at its entrails.

Sure enough, a day later this little charmer emerged. The maggot burst out from between the segments on the underside of the caterpillar.

The black structure that you can see at the head end seemed to be some kind of horny beak, that it used to cut an exit hole through the caterpillar's skin. Within two days eleven more of these maggots emerged and one by one ............

........ turned into a red pupa within a few hours of emergence. I suspect it's a tachinid fly (click here for pictures of the fly), although I won't know which one until the pupae hatch.

Gross

This is Tachina grossa, one of the largest and possibly the ugliest fly in Britain. It's as large as a bumblebee and spends its days feeding on nectar - harmless enough, unless you happen to be the caterpillar of a butterfly or a moth - in which case, like many other species of tachinid, it will lay its eggs on you. Its larvae burrow through their host's body wall and slowly consume it from the inside. Gross.

Apparently, T.grossa has a particular penchant for large caterpillars - especially those of the oak eggar moth and fox moth

This specimen was spending a sunny afternoon on a hillside at Stanhope in County Durham, feeding on marjoram flowers.

Tachina

Hogweed umbels attract all manner of insect visitors, including this very striking fly Tachina fera, which has a gruesome life history. It has two flight periods, from May to early June and from July to September.

This tachinid fly lays large numbers of small eggs on vegetation and when they hatch the grubs, alerted by vibrations from an approaching potential host noctuid moth caterpillar, attach themselves to it  and bore into its body, where they develop as internal parasites. There are numerous tachinid fly species, illustrated at the Tachinid Recording Scheme web site.