Spider wasps

Introduction

Spider wasps (family Pompilidae) are solitary wasps. They prey on spiders to feed their larvae or they parasitise other spider wasps. They do not form colonies to defend nests and are not aggressive.

Identification

Spider wasps are active in gardens during summer months. The spider wasp most commonly encountered is Cryptocheilus bicolor. This is a very large black wasp with orange wings and legs and a broad orange band around its abdomen. It holds its wings up when resting but flicks them when it hops and runs about on its long legs.

Habitat

Spider wasps live in urban areas, forests and woodlands, wetlands, heath.

Distribution

Spider wasps are found throughout Australia.

Feeding and diet

Spider wasps are often seen digging in soft sandy soil, dragging huntsman spiders along. Some species are known to bite off the legs of large hairy spiders, trimming them to make them easier to handle. Others have scales that help them walk on spiders' webs, allowing them to sneak up and attack the owner.

Other behaviours and adaptations

Spider wasps have a habit of flicking their wings on landing and moving with a jumping motion. The wasp does this when searching for a spider in bark, cracks, crevices or soil.

Life history cycle

The spider wasps you are most likely to see and hear are female wasps preparing nest chambers for their larvae. They dig a burrow using long spines on their front legs, then search rapidly around tree trunks and on the ground for a spider. On finding the spider, which may be as large as a huntsman or funnel-web and twice as heavy as itself, the wasp stings and paralyses it, and then drags or flies it back to the burrow. She then lays an egg on the spider's body, and seals it in a chamber or cell at the end of the burrow. The larva hatches and feeds on the body of the spider before pupating in a thin silky cocoon in the cell.

Some spider wasps sting the spider and lay an egg on it but do not dig a burrow to put it in. The spider is left where it was stung and the larva hatches and eats the spider. A small number of Spider Wasps steal spiders from other Spider Wasps for their own larva. This behaviour is known as klepto-parasitism (klepto: Ancient Greek for 'theft').

Danger to humans

Spider wasps have a potentially painful sting. However they are not aggressive and are unlikely to use their venom on humans unless extremely provoked. The best advice is to leave them alone. An ice pack may be used to relieve the pain of the sting. If there is evidence of an allergic reaction, medical attention should be sought.

References

• AGFACTS Information Leaflets
• CSIRO. 1994. Insects of Australia. CSIRO Publishing.
• Goode, J. 1980. Insects of Australia. Angus & Robertson, London
• Hadlington, P. and J. Johnston. 1982. An Introduction to Australian Insects. UNSW Press, Sydney
• Zbrowski, P. and R. Storey. 1995. A Field Guide to Insects in Australia. Reed Books, Sydney