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Does anyone know why many tachinids have large spines on the abdomen? I caught one today with relatively massive spines. Seems like such spines may be defensive but against what?
7 September 2007, NB, Canada. Length: 14mm

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Hi Tony,

this is really impresive.

cosmln

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this seems to be Tachininae > Histricia

Theo said before about the bristles on tachinids: "I suppose the bristles have a sensory function.
This makes sense when you are operation in thick vegetation, like canopies for instance. In grasslands, it might be less functional. That's where most of the Phasiinae are found."


One of the most impressive tachinid flies with bristles I've ever seen -
Paradejeania , or it could be called "cactus fly" --- http://tinyurl.co... ---
I would like, just for curiosity, if anybody knows a fly with much more brisltes than this one!

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I have always understood that the spines are sensory - being articulated and having nerve endings in the basal socket. But I can only guess they would need extra senses to find their hosts and I can't think how the bristles would help in this. Having vibration detectors would seem a rather low-tech and less accurate idea than, say, having larger and more sensitive antennae. I think most hymenopteran parasitoids rely mainly on their antennae to detect the presence of key detector chemicals in the environment. These can be the 'smell' of the host itself or the chemicals released from the host's foodplant when the plant has been eaten by the host.

Sorry, not a very comprehensive answer!

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Thanks Cosmin, Jorge, Chris. Sensory seems to be one function but I can't see why they would need such large spines. There has to be a 'more exciting' explanation. This species is a parasitoid of Arctiid caterpillars which in many species are excessively hairy.
Fly is probably Hystricia abrupta
In line with my earlier posts could I venture to say "Our Tachinids may not be bigger than your Tachinids, but they are a lot more spikey"