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I've noticed that numerous members of the Stratiomyidae featured in the Gallery have backward pointing spines emanating from the scutellum. Is this feature diagnostic of this Family? Is the arrangement and number of spines considered by the experts to be diagnostic to Tribe or Genus level?

The reason I ask what some may consider to be an elementary question (I am after all an amateur Dipterist), is that in accounts of Stratiomyid taxonomy, I cannot recall seeing this feature being mentioned. Much is devoted towing venation and antennal structure (which of course are important diagnostic features for many taxa right across the Diptera), but I find it puzzling that a feature as easy to spot in the field as this, seems to have received no attention in the admittedly few examples of the literature I've read.

If a specialist in this clade can enlighten me, I'll be grateful. :)

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The number of spines varies. Some have more than 2, some have 2 and some none at all. It is, thus, not diagnostic of the family.

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It is not diagnostic at family level, but it can be used, maybe with other characters, to separate subfamilies (e.g. more than 2 -> Beridinae).

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Not all Beridinae have more than 2 spines, though this is valid in the UK. I know in Hungary, genus Allognosta has no spines at all. Anyway, in general it cannot be used as diagnostic in Europe.

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I agree; that character alone can't be used for a complete determination. But I would like to know if my previous statement is correct or not: in other words, are there Stratiomyidae with more than two spines on the scutellum which are not Beridinae? If yes, what I said is wrong, otherwise it is correct even if it does not characterize all the Beridinae.

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No, it is not correct. For example Antissa of subfamily Antissinae, which occurs in the neotropics, has also more than 4 spines. But also some Pachygasterinae have more than 2 spines on the scutellum

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Thanks Ruud. One last question: is it valid for some local faunas? I read that it should be valid for French and Italian Stratiomyidae, but now I am no more sure.

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for some local fauna, sure! In the Netherlands yes. I guess also for France and Italy, but I am not 100% sure

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And there are other families with spines, too. Check, for example, Coenomyia ferruginea...

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And this is why I consult the experts. :)

Many thanks for illustrating this principle once again. I've learned several new pieces of data as a result. Keep up the good work everyone!