Trapdoor spiders are not dangerous to people. The Australian Museum says a brown trapdoor spider's bite may be painful and cause some local swelling, but it is not dangerous. The real risk is a mix-up. Brown trapdoor spiders are among the spiders most often mistaken for funnel-webs around Sydney, and a funnel-web bite is a medical emergency.
What does a trapdoor spider bite actually do?
A team led by emergency physician Geoffrey Isbister followed definite spider bites, each with the spider identified by an expert, from February 1999 to April 2003. The 2004 paper in the journal Toxicon, listed on PubMed, covers 49 bites from the big ground-dwelling spiders known as mygalomorphs. Sixteen came from funnel-webs, 13 from mouse spiders and 20 from trapdoor spiders. The trapdoor spider bites caused only minor effects. Two of the funnel-web bites caused severe envenoming that needed antivenom.
The same study found that 45 of the 49 bites were on the hands or feet, and that being bitten while gardening was strongly linked to this group of spiders. Severe pain, puncture marks and bleeding turned up across all three groups, so how much a bite hurts tells you little about which spider it was.
The Australian Museum advises seeing a doctor if symptoms from a trapdoor spider bite persist. If nobody got a clear look at the spider, treat the bite as a possible funnel-web bite and get medical help straight away.
How do you identify a trapdoor spider?
The brown trapdoor spiders of the Sydney region belong to the genus *Arbanitis* and measure 1.5 to 3 cm in body length. The Australian Museum describes a dusty look: golden brown hairs over the carapace, greyish or pale bars across the abdomen, and eyes set in two compact rows. Males have thick "boxing glove" palps at the front and a small double spur halfway along the first leg.
Funnel-webs differ in ways that matter:
- a glossy, sparsely haired carapace with no obvious body pattern
- eyes grouped closely together
- on the Sydney funnel-web, long spinnerets that are easy to see at the tip of the abdomen, where a trapdoor spider's are short and blunt
- on a male Sydney funnel-web, a spur on the second leg, not the first
Behaviour is no help. The Museum notes that a male trapdoor spider may rear up when threatened, so a spider standing its ground on the back step is not proof of a funnel-web. Most of the features above can only be checked at close range, which is too close to a live spider.
Why are trapdoor spiders in my lawn?
Despite the name, most brown trapdoor spiders never build a door. They dig open, silk-lined burrows with a collar of silk at the rim, and the Museum notes these burrows are often scattered over lawns. The spider waits just inside for crickets, moths, beetles and grasshoppers passing the entrance.
These spiders live for 5 to 20 years and take several years to mature. Females stay in or near the same burrow. Mature males leave to find a mate and wander in humid weather, and the Museum says Sydney brown trapdoor males wander throughout the year. That is when they turn up on patios and inside houses.
Kirrawee's southern border is the Royal National Park, and many houses in South Kirrawee look out over bush. A household there that finds a brown spider in the laundry most weeks, with a scatter of round holes in the back lawn, should book spider control in Kirrawee so a technician can identify both the spider and the burrows.
How do you tell a trapdoor burrow from a funnel-web burrow?
The Australian Museum's guide to garden holes gives the main differences:
- Funnel-web burrow: silk trip lines radiating out from the entrance, usually under cover or in a shady part of the garden
- Trapdoor burrow: either open with a collar of silk or closed with a lid, with no trip lines, and more often out in open ground
- Wolf spider burrow: around 2 to 3 cm across, often an open hole with no silk
The Museum also says holes are among the harder things to identify, so a hole on its own rarely settles the question. That matters here. It names the Woronora Plateau in the south and the Hornsby Plateau in the north as the two areas where Sydney's suburban funnel-webs mostly live, with sheltered burrows in bushland and gardens alike.
Bangor sits south of the Georges River and west of the Woronora River. A Bangor family with a shaded rockery along the side fence, and holes there with silk lines running out from them, should arrange quick spider control in Bangor rather than assume they are trapdoor burrows.
Should you leave trapdoor spiders alone?
The Museum's view is that brown trapdoor spiders probably help control garden pests and are not a major threat to people. That holds when you know the burrow belongs to a trapdoor spider. The hard part is knowing.
Gymea Bay runs down to the Port Hacking estuary, with Coonong Creek along the northern edge of the old locality. A Gymea Bay family whose toddlers play on a lawn dotted with silk-rimmed holes should book spider control in Gymea Bay and have every burrow checked, not just the one by the clothesline.
Lilli Pilli sits on the Port Hacking estuary, and its Lilli Pilli Point Bushland Reserve overlooks the Royal National Park. A household there whose dog keeps digging at holes along the garden edge, and who keeps finding big brown spiders on the back step after humid nights, should arrange spider control in Lilli Pilli before someone gets bitten while weeding.
Before you book
Note these details so the technician knows what to look for:
- where the holes are, such as open lawn, a shaded rockery or under a log
- whether any holes have silk lines running out from the rim
- what the spider looked like from a safe distance, including colour and any shine
- how often spiders turn up inside, and whether it is after humid or rainy nights
- whether children or pets play near the burrows, and whether anyone has been bitten
Send those details when you contact our team for pest control for Sutherland Shire households: call Sutherland Shire Pest Control Pro on 02 8360 3033 or email [email protected].