Crabro peltarius is a digger wasp with an outstanding feature: it has a swollen front leg, or at least the males have. What the purpose of these swellings is, is virtually unknown, but it is believed they play some role in love making. All species of the genus Crabro have these swellings and they differ in each species. In Holland there are three species, the males of which can be told apart after some study, often even in the field. Crabro scutellatus for instance has no or almost no yellow markings on its thorax. The other two species do. Crabro peltarius is the smallest of the other two, usually around 11 mm in length. Females are extremely hard to tell apart from other female Digger Wasps. All species are fond of warm, sandy soils, even though Crabro peltarius also nests in other dry soils. Th females digs some 30 centimeters into the soil and makes about 7 nest chambers. In it up to 9 flies are deposited for her off spring. Usually these are flies belonging to the house fly family, the stilletto family or the flesh fly family.
Crabro peltarius is a common species all over Britain, sometimes appearing in great numbers. It is on the wing from May to October.