Sometimes I have to hunt for specimens, sometimes specimens come to me - in this case the hoverfly (family Syrphidae) Helophilus pendulus - a common species, often seen in our garden, in this case found recently dead on a windowsill. It could have been swept into the bin, but not before treating it as an opportunity to look at external hoverfly anatomy in the following series of annotated images.
|Helophilus pendulus, front view - the 'face' is clearly seen with its dark vertical stripe in the centre, running across two protrusions - (1) the 'knob' and (2) the 'lip' above a strong indentation.|
|Underside of the abdomen showing the hind legs most clearly - the hind tibia is at least half pale in H. pendulus as shown by the red bar.|
|As in all true flies (Diptera), the 2nd pair of wings is reduced to a small drumstick-like 'haltere' which has a counterbalancing/gyroscopic function beating the opposite way to the wings in flight.|
|The large posterior spiracle (red arrow) near the base of each wing - used for breathing along with the anterior spiracle found just above the base of each front leg, just behind the head.|
|One of the 'feet' - the 5th (of 5) tarsal segments is shown by the red bar - there are two claws (solid arrow), each curving past a gripping pad (broken arrow).|
|At the base of the wing there are various tufts of hairs which help cover the various joints between body plates etc and prevent material getting in which might cause damage or interfere with movement.|
|The front of the 'face' - the central vertical stripe ends at the 'lip' above a deep indentation.|
|The antennae are short and consist of three segments (numbered here) - the 3rd is expanded and bears a long sensory bristle called the 'arista'.|
|The lenses of the compound eye.|
There is of course more that could be covered here (and I may expand some parts with more detail in future posts), even without dissection, but if you want to know more, the following are books I regularly use:
- Rotheray, G.E. & Gilbert, F. (2011). The Natural History of Hoverflies. Forrest Text, Cardigan. Does what it says on the cover. More morphological detail/images would be useful, but still good coverage of natural history.
- Stubbs, A.E. & Falk, S.J. (2002). British Hoverflies. BENHS, Reading. Keys to adults of British species, many plates, including dissections of genitalia, detailed species accounts, and useful background information.