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I see meral bristles are a key character of Tachinidae. What is a meral bristle?

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Meral bristles are the curved row of bristles on the meron (=hypopleuron). The meron is the triangular(ish) plate on the side of the thorax above and between the mid and hind coxae (the very basal segment of the legs). The presence of meral bristles distinguishes the Calliphoridae, Sarcophagidae, Rhinophoridae and Tachinidae (which have them) from the Muscidae, Scathophagidae, Anthomyiidae and Faniidae (which don't). The easiest way to find the meral bristles is to find the posterior thoracic spiracle, then look a little below and in front of it.

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See the first couplet in this illustrated key http://www.nku.ed...milies.htm ;) Robert

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Thank-you, gentlemen, I know what I am looking for now.

I can see that for photo identification, only a small percentage of photos are going to show this character well. On the other hand, I can now at least make the effort to get a good, enlarged, lateral view of the fly's mid-section.

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The term has been added to the Glossary, but in the future it will be edited in such a way that 'meral' will lead to 'meron' (= 'hypopleuron'). I will add an illustration that will immediatly show the meron with a row of setae.

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It's always good to know what makes flies fit into their various families - but the nice thing about having experience of our local fauna is that we can usually just know when a fly is a tachinid or muscid etc by sight and not have to look for meral bristles :) Of course, in all the families mentioned only the Tachinidae or rhinophoridae (I think) have a subscutellum, so that narrows it down a bit too :)