Mouse spiders can be dangerous, but serious bites are rare. The Australian Museum says some species carry venom potentially as toxic as the Sydney funnel-web's, yet few cases of serious envenoming have been recorded, and a mouse spider seems to inject less venom and may give a dry bite. Because a mouse spider is easily mistaken for a funnel-web, any bite from a big black ground spider should be treated as serious until a doctor says otherwise.
How do you identify a mouse spider?
Mouse spiders belong to the genus *Missulena*. They are stout, shiny black spiders from 10 to 35 mm long, and the feature that gives them away is the head. The Australian Museum describes a high, bulbous head and jaw region that looks swollen compared with the rest of the body.
The eastern mouse spider, *Missulena bradleyi*, is the forest-dwelling species of eastern Australia. Females are larger and solid black all over. Males are smaller and longer in the leg, and the eastern males carry a pale blue or white patch on the front of the abdomen. Some species have bright red jaws, which is where the red-headed mouse spider gets its name, but that one lives mainly in semi-arid inland Australia.
How is a mouse spider different from a funnel-web?
Both are large, dark spiders that live in burrows in the ground, which is why they are so often confused. The Australian Museum lists four features that separate mouse spiders from other big black spiders:
- a bulbous head and jaws
- a smooth, shiny carapace
- eyes spread across the front of the head rather than grouped close together
- short spinnerets, with a domed, button-like last segment
Funnel-webs, by contrast, have finger-like spinnerets at the end of the abdomen. Most of these features are only visible up close, and you should never get that close to a live spider. If a big black spider is moving across the patio or floating in the pool, treat it as a possible funnel-web and keep children and pets well away from it.
What does a mouse spider bite actually do?
Most bites cause little harm. Emergency physician Geoffrey Isbister reviewed every definite mouse spider bite he could find for a 2004 paper in the Medical Journal of Australia, listed on PubMed. He found 40 confirmed bites from around Australia. Only one caused severe envenoming, in a 19 month old child bitten by an eastern mouse spider. Six bites, all from eastern mouse spiders, caused local numbness, tingling or sweating, and five caused mild headache or nausea. Most people had no sign of envenoming, and no deaths were recorded.
That one severe case is the reason caution still applies. The Australian Museum advises giving the same first aid recommended for a funnel-web bite, and notes that funnel-web antivenom has worked in mouse spider cases. Since most people cannot tell the two apart in the moment, anyone bitten by a large black spider needs medical help straight away.
Why do mouse spiders turn up in yards and pools?
Mouse spiders live in silk-lined burrows in the ground, often closed with a trapdoor that blends into the soil. The eastern mouse spider seems to use a single flap-like door over a shallow burrow with a side chamber. Females rarely leave. The ones people find are mostly mature males out looking for a mate.
The Australian Museum says males wander from late summer until April or May, often in daylight and especially after rain, and they often fall into suburban swimming pools. Males take about four years to mature, and like most of their relatives they travel on foot, so a male crossing the lawn has usually come from a burrow somewhere nearby.
That makes bushland edges the most likely place to find them. Alfords Point is almost completely surrounded by the bushland of the Georges River nature reserve. A family there that keeps fishing black spiders out of the pool after autumn storms should book spider control in Alfords Point and have a technician confirm which species they are dealing with.
Illawong sits between the Georges and Woronora Rivers, with the Illawong Nature Reserve on its doorstep. A home there with a bush block behind the back fence and a big black spider found on the laundry floor after rain is the right time for urgent spider control in Illawong, since a funnel-web cannot be ruled out by eye.
Wet weather can bring out more than one. The Australian Museum records almost 300 eastern mouse spiders collected from a single backyard on the New South Wales Central Coast after flooding rain drove them from their burrows.
Should you worry if you find one?
One male mouse spider in the pool skimmer does not mean the house is overrun. What matters is where it came from and whether more are turning up.
Woronora sits in the river valley and is ringed by bushland. A Woronora household that finds black spiders along the back step every few days through autumn has a steady source close by, so book spider control in Woronora and ask the technician to check the garden edges and doorways where they are getting in.
The eastern side of the Kurnell peninsula is part of Kamay Botany Bay National Park. A Kurnell family with young children and a dog who keep meeting large black spiders on the patio should arrange spider control in Kurnell rather than guessing whether each one is a mouse spider or a funnel-web.
Mouse spiders also eat other spiders, beetles and ants, and the Australian Museum notes they can take small lizards and frogs. A yard with plenty of insects around the garden beds and lights gives them a reason to stay.
Before you book
Note these details so the technician knows what to look for:
- where you found the spider, such as the pool, a doorway or a garden bed
- what it looked like from a safe distance, including any red jaws or a pale patch on the back
- how many you have seen, and whether they turn up after rain
- whether bushland, a reserve or a creek sits close to the house
- whether anyone has been bitten
Send those details to our team for pest control services across the Sutherland Shire: call Sutherland Shire Pest Control Pro on 02 8360 3033 or email [email protected].