Trapdoor spiders

Introduction

Most trapdoor spiders are misleadingly named, as not all species make a door for their burrows.

Identification

Most trapdoor spiders, but not all, are misleadingly named, as not all species make a door for their burrows. For those species that do, these highly camouflaged entrances are almost undetectable, unless the door is open.

The common name covers several families of spiders, including the Idiopidae, Actinopodidae, Ctenizidae, Migidae and Cyrtaucheniidae. The Brown Trapdoor (Arbanitis sp) and the Spotted Trapdoor (Aganippe sp) spiders belong to the family Idiopidae. They include a wide variety of types, many of which are adapted to drier habitats.

They have short, blunt spinnerets. Males usually have a small double spur halfway along their first leg. Females are larger than males, and tend to be harder to identify to species level. These spiders tend to be quite timid, although the male may rear up if threatened.

Brown Trapdoor Spiders are dull brown spiders with a cover of paler gold hairs on carapace ('dusty appearance') which is usually weakly arched in side profile. There are often pale bars across the abdomen. Males have thick 'boxing glove' palps. Brown Trapdoor spider eyes are arranged in two compact rows.

Sigillate Trapdoor Spiders are brown spiders with a strongly arched glossy carapace and 4-6 hairless spots (sigillae) on top of the abdomen. Their eyes are arranged in three distinct rows.

Also, as there are several families of Trapdoor Spiders, identification to species level can be difficult without a detailed key.

Habitat

Brown Trapdoor burrows are open (without a trapdoor). Often they are found scattered over lawns. They can be distinguished from Funnel-web burrows by the absence of silk triplines around the entrance.

Sigillate Trapdoor burrows are made with soil or litter trapdoors.

Distribution

Misgolas group spiders are found in eastern Australia, especially in coastal and highland regions of New South Wales and Victoria. M. rapax is the common Brown Trapdoor Spider around Sydney. Aganippe group spiders are found across southern Australia west of the Great Dividing Range and include the Adelaide Trapdoor Spider, A. subtristis.

Feeding and diet

Common prey items include crickets, moths, beetles and grasshoppers, taken near the entrance to the burrow. Predators of Trapdoor Spiders can include birds, bandicoots, centipedes, scorpions, parasitic wasps and flies.

Parasitic Flies

Many species of flies love to parasitise spiders. In fact the family Acroceridae (small-headed flies) focus entirely on spiders.

Females dump batches of eggs near appropriate spider hosts, sometimes even in their webs. Newly hatched larvae penetrate through the leg joints of spiders , sometimes moving to the book lung area, where they enter a period of arrested development (diapause) that may last years while the spider feeds and grows.

Milichiidae flies are kleptoparasites and often steal food from spider webs and directly from the mouth of spiders.

Breeding behaviours

Mature male Trapdoor Spiders wander during humid weather in search of a mate. Mating takes place within the female's burrow. The male usually escapes being eaten in order to mate with several females, before dying.

The female will lay her eggs several months after mating, and protects them within her burrow. When the juveniles have hatched, they remain for several months before dispersing on the ground. They will then make their own miniature burrows. Each time the spider grows bigger, it has to widen its burrow and, in the door-building species, add another rim to the door. In undamaged trapdoors, annual concentric rings can be seen.

Trapdoors have a long life span, between 5 to 20 years, and take several years to reach maturity. Females stay in or near their burrows, whereas males leave their burrows once mature, and go in search of a mate.

Management

In urban areas Brown Trapdoor Spiders probably play an important role in controlling garden pests, and since they are not considered to be a major threat to humans, it is best just to leave them alone.

Danger to humans

Brown Trapdoor Spiders are often mistaken for Funnel-web spiders but their bites are not dangerous. Local pain and swelling may occur. Sigillate Trapdoor Spider bites may also cause local pain and swelling. There is one report of unspecified 'severe effects' from a Sigillate Trapdoor Spider bite.

Seek medical attention if symptoms persist. Collect spider for a positive identification.

References

• York Main, B. 1976. Spiders. The Australian Naturalist Library, Collins, Sydney.
• Brunet, B. 1996. Spiderwatch: a guide to Australian spiders. Reed/New Holland.
• Simon-Brunet, B. 1994. The Silken Web: a natural history of Australian spiders. Reed Books.