Paul writes: the Orange-backed Tachinid (Tachina fera) is a fantastic fly. It’s quite large, reaching 16mm long and easily recognisable by its colours and spiky appearance. It is fairly well distributed throughout England and Wales but less common in Scotland. I usually see them in August and September, I found this one recently at Harlow Carr Gardens near Harrogate. They are good pollinators and can be seen in most habitats where there are plenty of flowers, umbellifers are particularly popular.
Tachinid flies can usually be identified by the bristles on their abdomens, these are much longer and spikier than on other flies. Sometimes they are referred to as Punk Flies. The larvae of Tachinids are parasitoids of caterpillars and larvae of other insects. The Orange-backed Tachinid favours the caterpillars of moths. Eggs are laid on the leaves of the food plants of their hosts. The young larvae will then enter the body of the caterpillar and devour it as they develop, eventually killing it.
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Another very interesting read. Is it known if the larvae enter the caterpillar by being eaten or by burrowing eating their way in?
Amongst tachinid flies there are several strategies for getting the larva inside the host. Some species lay eggs directly onto the host but many adopt a passive approach in which they lay eggs onto the leaf surface. Of these, some lay small eggs that are ingested unwittingly by the host and hatch within it but in others the eggs hatch on the leaf and then attach themselves to a passing host. I believe T fera is in the latter category: “The first-instar larva lies flat on the leaf, stimulated by vibration to take up the host-searching posture” (Belshaw, R. 1993. Tachinid flies. Diptera: Tachinidae. Handbooks for the identification of British Insects. Royal Entomological Society of London 10).
Thanks very much Jonathan.
Isn’t nature wonderful?
I was sure my handbooks would not have the information.
Thanks Alex for your interest and Jonathan for your detailed reply. The life cycles and strategies of different insects fascinates me. I am sometimes amazed at the things we have discovered and also what we still don’t know.