Posted by: scrubmuncher | June 18, 2010

Hats off to the digger wasps

Surprisingly, there isn’t any government help for single mums in the insect world, so female digger wasps (hymenoptera: sphecidae) wear their little tarsi to mere nubs trying to make ends meet and rear their brood. These single mums use their all too short adult lives to build and provision a nest to see their offspring through their larval development. This is no mean feat by any stretch of the imagination. Take this little digger wasp – Crossocerus megacephalus:

This adult Crosscerus megacephalus was reared from the nest constructed by its mother. You can train them to keep very still (Ross Piper)

This species of digger wasp uses its mandibles to excavate a nest in dead wood by enlarging and modifying the feeding tunnel of a wood-munching beetle larva. Typically, the nest has a main tunnel and a small number of side galleries, each of which will serve as a nursery for an individual wasp larva. The female C. megacephalus must stock each of these galleries with food, a job she’s well suited too as she’s a predator par excellence. Her quarry are flies and she seeks these poor insects out and dispatches them with singular efficiency. The flies she goes for are only a little smaller than her, agile and fast flying, so she needs razor sharp senses and flying skills to follow her prey and tackle it in mid-air. Once the wasp has made contact she doesn’t let go and the pair hurtle to the ground where this incredible little predator administers a paralysing sting. The doomed fly is clutched to the underbelly of the wasp and she zips off back to her nest to deposit the prey in one of the larval galleries she has tirelessly prepared.

Such a predatory feat is amazing in its own right, but even more incredible is that the female has to do exactly the same a further 15 or so times to stock each gallery, and there may be as many as five galleries. In her fleeting adult life, which may be as short as a couple of months this amazing little wasp finds, tackles, paralyses and deposits at least 75 flies for its young to feed on, to say nothing of her tireless efforts in locating and constructing a nest in the first place.

Here are the contents of one larval gallery contructed and stocked by a female Crossocerus megacephalus. The flies (below) are rhagionids (Chrysopilus asiliformis) and were all caught by the female wasp to provision one of the galleries in its nest. The cocoon (lower right) is what the adult wasp hatched from (the adult wasp in the photo completed its development and scoffed all the flies provisioned by its mother). The nest was found in a small hazel (Corylus avellana) stump, Hatfield Forest, Herts, UK (Ross Piper).

For this, I take my hat (a fine pith helmet) off to the  C. megacephalus and give it a stout pat on the back. This is but one part of the life of one species of digger wasp. Much of what digger wasps get up to, often under our very noses is a mystery, all the more reason to take a closer look at them.



  1. Great stuff, Ross. I hope to find time to catch up on the rest of your blog.

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