COLEOPTERA > ADEPHAGA > Dytiscidae

The Adephaga suborder includes around 150 species of water beetle in six families; Gyrinidae (Whirligig beetles), Haliplidae (Crawling water beetles), Noteridae (Burrowing diving beetles), Hygrobilidae (Screech beetle) and Dytiscidae (Diving beetles).

Dytiscidae is the largest family with approximately 120 species, all of which are predatory to some degree at both the larva and adult stages. They are adapted for life in the water, streamlined with an oval shape where the head almost appears to be part of the body. Although some species are very small, most are medium-sized with an overall body length of 6-15mm, others a bit larger, and the largest in the Dytiscus genus ranging from 22-32mm or, in the case of the rare King Diving Beetle [Dytiscus dimidiatus], up to 38mm.

There are six subfamilies, although most species are grouped within either Hydroporinae which is a large assemblage of 64 small (<6mm) beetles that are often found in shallow habitats, Agabinae and Colymbetinae that collectively include 36 medium-sized species that I believe are usually found in vegetation and sediment around the edges of both still and running water, and Dytiscinae which includes 14 large diving beetles.

I have to admit that when the first version of this section of the website was drafted, I ignored water beetles entirely as I didn't expect to encounter any during my normal insect-hunting ventures. However, that may now change having read a bit about them after finding the rather stunning individual featured below. I also discovered that water beetles are surprisingly well covered in respect of identification guides, which can't be said for many beetle families.

The Great Diving Beetle [Dytiscus marginalis] is the 'type species' often used to represent the family in general guides. It's common and widespread but, despite its familiar appearance, there are other similar species that have to be considered, so identification isn't as straightforward as you'd think for such a distinctive looking beetle. They are large, typically around 26-32mm body length, elongate-oval with a continuous outline. Males are shiny dark brown to black, to some extent green, more noticeable when submerged or wet. Females are dull brown with the elytra heavily ridged. The pronotum is dark with broad pale margins on all sides and, importantly, the underside of the body is all yellow rather than yellow and black.  

The specimen that I photographed in the garden was actually found by our cat on vegetation bordering our small wildlife pond. It was a welcome, albeit rather unexpected, discovery as I've never seen any water beetles in the pond before or at least none bigger than a few millimetres. But, of course, they can fly and that's why even freshly dug ponds can be colonised surprisingly quickly.

New family added, July 22 (v.1)