The whirligig beetles are familiar to anybody who has had more than a cursory look at still or slow-moving water during the warmer months. They are relatively small, dark coloured beetles that swim round and round in circles, apparently mindlessly, but certainly with their own agenda. In the British Isles there are 12 species (one of which is probably only from Ireland) in two genera. Some of them can be distinguished using characters visible at relatively low power magnification but for others close observation of the fine surface sculpturing of the elytra is required at high magnification. Even then identification will sometimes be tentative without examination of the male or female mating apparatus. A key to the British species is given below. It should be noted that it is for use with the beetles dry, with good illumination and binocular magnification of up to around x50. This family is not for the faint-hearted! If you wish to try your hand at the dissection then reference should be made to Laurie Friday's work (referenced in the document below).