The genus Ectemnius contains some of our larger and more colourful aculeates. All ten British species in this genus have black gasters which are boldly marked with yellow transverse bands or paired lateral spots. Most are locally distributed throughout much of southern England, the number of species and their degree of abundance decreasing northwards. Only three species are known from Ireland (Stelfox, 1927) and a similar number from Scotland.

Of the three species of Crabro which occur in Britain, C. cribrarius is the largest. Male Crabro can be readily distinguished from other medium-sized British and Irish sphecids by their conspicuous fore-tibial shields.

The 'median wasp' is a very large social species, most individuals being second only to the hornet, Vespa crabro, in size. Queens of D. media also resemble V. crabro in their mainly yellowish-orange coloration. The gasters of many workers are very dark, with narrow yellow bands. Most colonies are rather docile; others seem to be very aggressive, attacking with little provocation (Welch & Irwin, 1995).

Specimens of the 'Saxon wasp', the second species of social wasp to have recently colonised England, are more difficult to identify in the field than its congener D. media. It is a very close relative of D. norwegica but lacks the pair of red spots on the second gastral tergum (but beware, these markings are also absent in some D. norwegica).

Ectemnius cavifrons is one of the largest and most common species of its genus in Britain.