ARC's reserves are havens for many organisms, not only reptiles and amphibians. Warm dry heathlands, for example, are home to a large proportion of our 500 species of nest-building wasps and bees. Many dig burrows in bare, sandy soil, so areas created with species like sand lizards in mind provide excellent habitat. Jeremy Field (University of Exeter) tells us more.

Under the auspices of ARC, we have recently been investigating the biology of Sand Wasps (Ammophila pubescens) at Witley Common in Surrey. A female Sand Wasp digs a short burrow in the ground, then seals the entrance with a plug of sand and tiny pebbles. She next hunts for caterpillars on nearby heather plants. Once found, a caterpillar is paralysed by stinging, carried back to the burrow, dragged inside and a single wasp egg is glued to it. The mother then re-closes her burrow and waits a few days. After checking that her egg has hatched successfully, she adds further caterpillars as food for her growing offspring. Because they are not dead, but paralysed by the wasp’s venom, the caterpillars remain fresh. When it has finished eating the caterpillars, the wasp larva spins a cocoon and overwinters in the burrow, before emerging as an adult the following year.

Marking wasps individually with dots of paint has led to some surprising findings. It turns out that each female wasp typically has several burrows on the go at once – sometimes as many as eight. She not only remembers their locations, but also their ages: offspring are fed one at a time, oldest first. Females also behave like cuckoos. If she comes across another female’s burrow entrance, a Sand Wasp will open it. She throws out the egg-bearing caterpillar and replaces it with a new caterpillar and egg of her own. Sometimes the nest owner detects the cuckoo offspring, probably because it is younger than she expected. If so, she in turn throws it out, replacing it with yet another egg. Occasionally we have seen eight eggs replaced, tit-for-tat, at one nest! Eventually, an egg is usually accepted by both parties, and both may end up feeding the offspring. Jointly fed offspring grow larger than usual, because of the double rations. 

Other Sand Wasps are not the only threat. Satellite Flies dump their maggots into open wasp burrows, and a Bee Fly, nationally rare but common at Witley, may flick in her eggs. Both of these parasites spell doom for the unfortunate wasp larva. There can be as many as 200 wasp and bee species nesting on a heathland in southern England, many with their own specialized parasites. By creating the right conditions for lizards and snakes, ARC is simultaneously helping to preserve a fascinating and significant piece of our invertebrate fauna.

Photo credits: J. Field, M. Blösch, Y. Field