They have alarming fangs and lurk unseen in their burrows for decades. They are commonly found in lawns and gardens. Would you be able to recognise a brown trapdoor spider?
Common name: Brown trapdoor spider
Scientific name(s): There are a large number of trapdoor spiders in Australia, an estimated 400 species, many of which are undescribed. They belong to several families of spiders, including the Idiopidae, Actinopodidae, Ctenizidae, Migidae and Cyrtaucheniidae. Brown trapdoor spiders are generally in the family Idiopodae. Often the name ‘brown trapdoor spider’ is used to describe a species in a particular location, e.g. the Sydney brown trap door spider, Arbanitis villosus or Misgolas rapax and the Brisbane brown trapdoor spider, Arbanitis longipes.
Other common names: Tube spiders. Spiders in the family Idiopidae have also been called spiny trapdoor spiders, armoured trapdoor spiders and true trapdoor spiders.
Geographic distribution: Present in all parts of Australia, but less common in the hottest regions. They prefer moist ground, often clay-rich soils, and may live on flat ground or embankments. There appears to be more species and a higher density of spiders on the moister east coast of Australia.
Description: Brown trapdoors resemble tarantulas, with a body several centimetres long. They have eight tiny eyes close together on top of the head, arranged in a rough X, and long legs. Most Arbanitis species are mottled brown or orange-brown, with paler or metallic hairs over most of the body. Although sometimes confused with funnel-web spiders which tend to like similar environmental conditions, they lack the shiny carapace of the funnel web spider and also have short spinnerets (the funnel-web has distinctly long spinnerets).
Males in most species have a spur on the first leg, used to hold the female’s jaws during mating, but his pedipalps are long and robust enough that they can be easily mistaken for another set of legs. Also, just to confuse identifications, some species lack the spur, and some individuals lack them even in species that usually have them! Many species are very similar in appearance and can only be distinguished by closely examining the males. Females are generally larger and stockier than the males.
Habitat: Despite the common name, trapdoor spiders build every type of burrow possible, some with trapdoors, some with reversed trapdoors, some with open holes that may be lined with dried leaves and silk, some with palisades roughly 5 cm tall with thin or thick lids, and some have open tubes that extend 20 cm or more above the ground. The Sydney brown trapdoor spider generally has an open tunnel with a silken rim (but no trip lines). The Brisbane brown trapdoor spider also has an open tunnel but binds leaves around the opening with silk.
Females will not leave the burrow unless disturbed, flooded out, or accidentally unearthed. Males will leave their home to seek a mate, at the end of their lifetime.
Life-cycle: Trapdoor spiders and other mygalomorphs mate at best once a year, with the male usually being eaten by the female after mating or dying soon after. The young emerge from an egg sac laid inside the mother’s burrow, and remain there for one or two moults, before making their own burrows nearby, usually within 30 cm of the maternal burrow.
Spiders mature after 5-7 years, when the males leave their burrow in search of a mate. Based on their size, females of A. longipes may live up to 10 years, but other trapdoors have been know to live longer.
Pest status: Although they are commonly encountered in gardens, they generally do not come inside homes and therefore are not considered a pest. However, they do present a potential bite risk. Arbanitis of either sex will rear up defensively if threatened. Their long fangs may cause a deep and painful wound, along with redness and swelling, but are not considered a serious medical threat.
However, brown trapdoor spiders are easily confused with other large mygalomorphs, including the funnel-webs, mouse spiders, and wishbone spiders. As such, if positive identification cannot be achieved, any bite from a large black spider should be treated as a per a funnel-web bite: immobilise the victim, apply a pressure bandage and call for medical help.
Treatment: No treatment is required. Males will not linger around houses, and the females will not leave their burrows unless forced. If encountered in a garden, both can be gently encouraged to move on with a broom.
Other types of spiders.
Daniel Heald, technician and entomologist