DIPTERA > BRACHYCERA | Higher Diptera

LOWER BRACHYCERA > ASILOMORPHA > Asiloidea > Therevidae (14 species)

(subfamilies: none)

One of the main characteristics of this family is the conical shape of the abdomen; the form of which has been likened to a stiletto, as in a pointed stabbing implement. When at rest, these species have an alert stance, looking as though they’re standing on tiptoe on their long, slender legs. Wings are normally held in a narrow delta shape or closed over the back, which often obscures the shape of the abdomen. They could be confused with snipeflies, but one noticeable difference is the presence of strong leg bristles, which are particularly evident on the tibiae. They also resemble some of the predatory robberfly species.

Most species are associated with dunes, sandy soils and river banks, and many are only found elsewhere in the country. In fact, as far as I can deduce, Thereva nobilitata, Thereva plebeja and possibly Thereva fulva, are the only species I’m likely to encounter locally. They could be found resting on the foliage of bushes, brambles or nettles, but would not be seen feeding at flowers.

Thereva nobilitata is by far the most frequent British species but, although its distribution is widespread, is still regarded as elusive rather than common. There are nine Thereva species on the British list and most are variable, but this species is particularly so as can be seen in the following photos. Males are quite dark with a drab brown thorax, females brighter, almost golden when fresh, but look different as hairs rub off. The far less common Thereva plebja species could be confused with Thereva nobilitata, more so in the male, but it’s much darker since the tergites are extensively black in front with an inconspicuous grey band behind, and with the actual hind margin being pale. The thorax is dark greyish black. And the wing cross veins are clouded. Although I’m as sure as I can be regarding the id of the male in the photo below, positive identification is only possible through examination of its reproductive organs which, without going into detail, is where the common name for the species, Crochet-hooked Stiletto, is taken.

Updated, July 22 (v.2)