The Tachinid Fly

A tachinid fly

A tachinid fly, Tachina fera

If you have ever spent time next to a pond, you will have seen these hyperactive creatures, sparring with one another in a most unfriendly manner. They are as stripey as wasps or hoverflies, but instead of hovering or buzzing, they dart and joust like little armoured knights. One minute they are sitting happily on a lilypad, the next they are flying a vicious skirmish with another fly, and then they settle down again, until the next interloper appears.

This species has no common name, but its Latin moniker is Tachina fera. It is usually found near water, and it has a great liking for water mint, although there is none in my pond (yet). There are more than eight thousand different species of Tachinid flies (with two hundred and seventy five species in the UK) but the one characteristic that they share is bristliness. In the picture of a Tachinid fly in my Garden Wildlife book there are bristles everywhere – on the legs, on the thorax and especially on the abdomen. I cannot report back on this from life as these flies are  speedy and elusive, zooming away at the first hint of vibration or shadow. However, here is an image showing how hairy these flies are when seen close up:

An extremely hairy fly By Siga (Own work) [GFDL ( or CC-BY-SA-3.0-2.5-2.0-1.0 (], via Wikimedia Commons

An extremely hairy fly By Siga (Own work) [GFDL ( or CC-BY-SA-3.0-2.5-2.0-1.0 (], via Wikimedia Commons

Tachina fera lays her eggs on the bodies of caterpillars, particularly those of noctuid moths. The eggs hatch, and parasitize the caterpillar. Once the fly emerges it seems to spend most of its time protecting its airspace, and I have never seen one feeding.

Tachinid Fly 4 BlogAs I watch the fly ‘patrolling’ its tiny ‘territory’, I realise that I have no idea at all what it is actually doing. I have made all kinds of statements about the darting about and sparring, but in truth I am just extrapolating from behaviour I’ve seen in other animals, and who knows if I was even right about  them? I feel a deep need to interpret what I see, to make sense of it.  And yet, I am aware that I walk a line between looking at animals and plants in terms of all that we have in common, and recognising how profoundly different they are, both from me and from one another. How can we celebrate all the things that we share without reducing everything to a commonality that has no room for the extraordinary variety of the creatures with which we share the planet?

The fly darts up, turns, lands back on the lilypad. It rubs its front legs together as if washing its hands, then runs a front leg over its big red eyes. It is poised, always, for flight, like a cat crouching before the pounce. When I come back an hour later a shadow has fallen over the pond, and all the frenzied activity of the morning has died down. I know nothing of where the fly has gone, just as I know so little of the lives of all the animals in the garden when I’m not actually watching them. I live in the midst of mystery.

Tachinid Fly 2 Blog



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