Eristalis pertinax (Scop.)   
(a hoverfly)

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Hexapoda
Class: Insecta
Order: Diptera – true flies

British distribution: Widespread.
World distribution: Europe, widespread.

Eristalis pertinax
Eristalis pertinax, closer view
Eristalis pertinax at rest on bramble leaf, Carmarthenshire, July 2003.

Eristalis pertinax is one of the larger hoverflies (family Syrphidae). Hoverflies are classic Batesian mimics, harmless but closely resembling bees or wasps (order Hymenoptera), and E. pertinax is one that closely resembles the Honey Bee, Apis mellifera, not only in appearance but also in behaviour as it visits flowers. However, as a true fly it has just a single pair of wings, the hind wings having been modified into the tiny, drumstick-like halteres, which provide balance in flight. The males commonly hover in woodland clearings, aggressively defending small territories (Stubbs & Falk, 2002).

Eristalis pertinax, wing venation
Hoverfly wing
Hoverflies are unusual amongst flies in having two outer cross veins close to the wing margin, with most other flies having only one such cross vein or none at all.
The vena spuria, a false vein, is diagnostic of the hoverflies.
The distinctive venal loop is characteristic of Eristalis and a few closely related genera (tribe Eristalini).

The larva of Eristalis and related genera is the "rat-tailed maggot" so called because it has a long, rear, tail-like, extendable breathing-tube, enabling it to live submerged in organically polluted, deoxygenated aquatic sediments.

E. pertinax is a common and fairly easily recognised species, though it can be confused with the Drone Fly, E. tenax. The latter has a broader facial stripe between the eyes and little or no yellow on the legs - specifically the tibiae of the hind legs are dark in E. tenax whereas they are distinctly bicoloured in E. pertinax and the front tarsi (sequences of lower leg joints) of E. pertinax are orange. Whereas the abdomen is tapering in E. pertinax, causing it to resemble a worker Honey Bee, the abdomen is more nearly cylindrical and "chunkier" in E. tenax, so it is more like the drone. A common but smaller species otherwise resembling E. pertinax in general appearance is E. interruptus, which has black front tarsi.

The excellent and definitive account of British hoverflies, much used as a source here, is:
•   Stubbs, A.E., & Falk, S.J. (2002). British hoverflies. An illustrated identification guide, ed. 2, British Entomological and Natural History Society, Reading.

© A.J. Silverside
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