Hogweed umbels are a hive of activity at this time of year, with a constant procession of insects arriving on the flat plates of flowers to either feed on pollen and necter, mate or hunt other insects. This visitor is a male slender-bodied digger wasp Crabro cribrarius which, as far as I could tell, was after plant food rather than animal prey. The female, on the other hand, is a hunter of flies, paralysing them with her sting and then incarcerating them in chambers at the end of an 8 centimetre-long tunnel that she digs in sandy soil. Take a close look at the insect in the picture and you'll notice something odd about its front legs, where one leg segment is broadened out into a flat plate. It looks like it's wearing boxing gloves.
There's a picture of a female here.
Johann Fabricius, the 18th. century entomologist who named this species, gave it the epithet cribrarius -a word meaning sieve - on account of the pattern of pale markings on the foreleg plate that makes it look like a sieve (or more like a collander, if you spend a lot of time in the kitchen). As far as I know, no one has every adequately explained what that odd-shaped leg is for. Not for digging or hunting - the female, which lacks this feature, does that. The suspicion is that males have them as an aid to gripping their mates during mating.
Crabro cribrarius is only about a centimetre long, so is easily overlooked. This one was photographed on the cliff path between Craster and Howick, on the Northumberland coast, last Saturday.
Posts
