What's in the box? No.8 - shiny shiny jewels

In my previous article about beetles-by-post, I mentioned that I would soon get onto the reed beetles (family Chrysomelidae; subfamily Donaciinae) that I found in the first batch I looked at. Always one to keep my promises, here is the first one presented in all its bright and bejewelled glory...

The first of the two reed beetles; note the bright green elytra and pronotum and the long back legs.

This specimen is about 8mm long, not including appendages, and even at this magnification the rows of punctures on the elytra are obvious, as are the wrinkles on the pronotum. However, lets look at some closer detail - after all, the reed beetles look as if they should be easy to identify (they are brightly coloured and reasonably large), but species can in fact be quite difficult to separate as the colours are variable as are some other features such as spines on the legs.

A closer look - see the dents on the side of the pronotum and the pattern of wrinkles with a longitudinal marks down the middle. You can also see that the elytra are hairless.

A close-up of the head; this may not be needed for identification, but the fine detail is fascinating, including the sculpturing (a central groove matches the one on the pronotum), prominent eyes and tiny hairs.

Even closer still; looking at the fine detail of the elytra, you can see the punctures clearly and on the surfaces between them some fine 'microsculpturation' i.e. the surface looks shiny but isn't completely smooth.

Some of these features such as the pronotal wrinkles and the precise form of the central pronotal groove (e.g. whether it is complete or broken) are used in identification, but some essential features mean turning the beetle over.

Ventral (underside) view; the key structure here is the hind leg. Note the reddish colour at its base (the rest of the femur is dark) and the blunt tooth near the 'knee' joint with the tibia. The extent of red colour (if any) and the number/shape of hind tibial spines can be important features for identifying reed beetle species, not forgetting that some features (such as the spines) may vary between males and females - males have two femoral teeth, females have one as here although this is sometimes missing.

Zooming in on the hind tibia, a series of tiny teeth are visible on the ventral ridge.

This combination of features means this is a female Donacia versicolorea. This species is found distributed locally across Britain and is a good example of a variably coloured species - it can be darkly coloured or bronze. Adults are usually found in July and August, though this one was collected on 23rd June 2011, a little earlier than usual, though this year did have an early spring. The details above separate it from the similar D. crassipes which is larger (9-11mm) and has a pronotum that is microsculptured but not strongly wrinkled as here. D. dentata shares many features as well, but has dull elytra and two femoral teeth in both sexes.

If you are interested in British reed beetles, Menzies & Cox (1996) is excellent (and available as an unbound reprint for a few pounds) and will form the basis for the Donaciinae section of my forthcoming key to British chrysomelids. It also provides keys to separate the different genera (Donacia, Plateumaris, Macroplea), something I will cover in a subsequent article.


Reference

Menzies, I.S. & Cox, M.L. (1996). Notes on the natural history, distribution and identification of British reed beetles. British Journal of Entomology and Natural History 9: 137-162 + 2 pp. of colour plates.