Mouse (Missulena)

Physical description and identification

Missulena is a genus of mygalomorph spiders — the ancient lineage that also contains tarantulas, Australian funnel-webs and the true trapdoor spiders. Around twenty species are recognised. All but one are Australian; Missulena tussulena lives in Chile, reflecting the ancient Gondwanan split rather than any recent introduction. The family Actinopodidae also contains the South American genera Actinopus and Plesiolena.

The impression is of a small, heavy, polished tank of a spider: a broad carapace, high at the front and shiny, short thick legs, a rounded abdomen, and short spinnerets tucked under the rear — nothing like the long spinnerets that project behind a funnel-web.

Adults

• Size: from about 10 mm in the smallest species to around 35 mm in a large female. Females are stockier and heavier; males are smaller-bodied with longer legs.
• Colour and sexual dimorphism: extreme. Females of almost every species are uniformly glossy black. Males vary by species and are often strikingly marked — the male red-headed mouse spider (M. occatoria) has a blue-black body with bright red to orange chelicerae, and the male eastern mouse spider (M. bradleyi) a pale bluish-white patch at the front of the abdomen.
• Eyes: the key field character. The eight eyes are spread in a wide group across the front edge of the carapace rather than clustered on a small mound, giving the genus a face unlike any other Australian mygalomorph; see spider eyes.
• Fangs: large and paraxial — they strike downward in parallel rather than pinching sideways as in wolf spiders and other araneomorphs, and are long enough to penetrate a fingernail.

Eggs and egg sac

The female builds a rounded white egg sac deep in the burrow, typically holding sixty or more eggs, and stays with it. Everything happens below ground: nothing is visible at the surface except the door.

Spiderlings

Spiderlings hatch through the warm months and remain in the maternal burrow for several months, moulting once or twice before leaving, usually in autumn. In M. occatoria the young disperse by ballooning on silk threads — remarkable, because almost all mygalomorphs disperse on foot. Males take around four years to mature and die soon after their wandering season; females hold the same burrow for many years.

The burrow — not a web

Mouse spiders build no capture web. They dig a shaft, usually 20–30 cm deep and sometimes much deeper, and line it with silk. The entrance is closed by a hinged trapdoor of silk and soil, and many species add a second door and a side chamber part-way down, working as both bolt-hole and flood protection — burrows are often on creek banks. Some radiate short silk trip-lines from the rim. The spider waits just under the door, feels the vibration, throws it open and strikes. Entrances are easy to miss: a neat disc of soil a centimetre or two across, in a bank, a lawn or beside a path. See our guide to spider webs.

Where mouse spiders live

The genus is effectively Australian. Species occur in every mainland state and territory, from wet eastern forests to arid inland scrub — see spiders in Australia and the guides for Queensland, Sydney, Victoria and Brisbane. M. occatoria is the most widely distributed and reaches semi-desert country; M. bradleyi follows the eastern seaboard and is the species most often met in suburban gardens.

Habitat is a matter of soil rather than vegetation: ground they can dig and hold — creek banks, drainage lines, embankments, open woodland floors, garden beds, lawns and path edges. Because so many burrows sit exactly where people walk, mow and garden, contact is more common than the spider's secretive life suggests.

Males are the ones people see. Unlike most mygalomorphs they wander in broad daylight in search of females, typically in late summer and autumn and very often the day after heavy rain. A glossy black spider the size of a coin walking across a lawn in daytime in Australia is far more likely to be a male Missulena than a funnel-web.

Are mouse spiders venomous?

Yes, and this is a genus where the answer matters. The widely repeated line that mouse spider venom is "not very strong" for people is wrong. Work on the male eastern mouse spider (M. bradleyi) identified a peptide toxin, δ-hexatoxin-Mb1a, that acts on sodium channels in essentially the same way as robustoxin, the main toxin of the Sydney funnel-web spider. Some Missulena venom can therefore cause the same kind of severe neurotoxic envenoming as one of the most dangerous spiders in the world.

Two things temper that. Severe envenoming from Missulena is genuinely rare: reviews of confirmed bites in Australia show the great majority produce only local pain, and a high proportion are dry bites with no venom injected. And when serious envenoming does occur, funnel-web antivenom is effective and has been used successfully, including in a documented case in a young child.

So the outcome of any individual bite cannot be predicted at the scene, and an effective treatment exists in hospital — which is why every mouse spider bite should be handled as a potential emergency until a doctor says otherwise. They belong on any list of Australia's most venomous spiders.

Can mouse spiders bite, and what should you do?

They can, and they are capable of a determined bite. Mouse spiders do not seek people out, but a cornered individual will rear up, display its fangs and strike repeatedly. Most bites happen when a wandering male is picked up, trodden on barefoot or trapped against skin, and bites to children and pets are over-represented for that reason.

Reported symptoms range from nothing at all through sharp local pain, puncture marks, swelling and sweating, up to — rarely — the full neurotoxic picture of funnel-web envenoming: profuse sweating, copious salivation and tearing, muscle twitching around the mouth and tongue, nausea and vomiting, abdominal pain, severe hypertension, breathing difficulty and collapse. Children deteriorate faster than adults, and serious envenoming begins within minutes rather than hours.

First aid for a suspected mouse spider bite, following Australian resuscitation guidance for big black spider bites:

• Call emergency services immediately — 000 in Australia — and keep the patient still. Movement pumps venom into the circulation.
• Apply a pressure immobilisation bandage: bandage firmly over the bite with a broad elastic bandage, continue up the whole limb, and splint it to stop it bending. The pressure should be as firm as for a sprain, not a tourniquet, and fingers or toes must stay warm and pink.
• Keep the patient lying down, calm and warm, and give no food or alcohol.
• Do not wash the bite site, cut it, suck it, or apply a tourniquet or ice.
• If it is safe, photograph the spider or collect it in a sealed container — identification guides treatment.
• Go to hospital even if the patient feels fine. Antivenom and monitoring are hospital decisions.

Ecological importance and behavior of mouse spiders

A mouse spider is an ambush predator anchored to one hole. The female sits just beneath the trapdoor with her front legs against it, detects vibration through the soil, flips the door and strikes in a fraction of a second, dragging the prey underground. The diet is mostly ground-active insects — beetles, cockroaches, crickets, ants and centipedes — plus other spiders and occasionally small skinks and frogs.

Natural predators: spider-hunting wasps are the specialists, paralysing an adult and sealing it in a nest as living food for a larva. Scorpions and centipedes take spiders inside burrows; bandicoots, kookaburras, currawongs and reptiles take wandering males.

Ecological role: burrowing aerates soil and creates shafts that channel water and shelter other invertebrates, and as sit-and-wait predators they exert steady pressure on beetle and cockroach populations.

Seasonal behaviour: the annual cycle turns on the males. They mature after roughly four years underground, then walk in daylight through late summer and autumn, with a strong pulse of activity after rain. A male that finds a burrow taps at the door, is admitted, mates and dies within months. Females stay put, feeding and producing sacs for many years in the same shaft. Spiderlings leave in autumn — in M. occatoria on wind-borne silk.

Relationship with humans: low-frequency, high-stakes. Mouse spiders cannot climb smooth walls and do not colonise houses the way a redback does. The precautions are simple: wear shoes and gloves in the garden, check around pools and drains after rain, teach children not to touch glossy black spiders walking in the open, and never handle one to identify it.

Species in the genus and similar spiders

Quick facts

Did you know?

• The genus was described in 1805 by Charles Athanase Walckenaer. The common name is a misnomer: early accounts assumed the spiders dug deep burrows like a mouse, and nothing about the shaft or the animal is especially mouse-like.
• The red-headed mouse spider is one of the very few mygalomorphs whose spiderlings balloon. Wind dispersal on silk is almost unheard of in this ground-bound lineage, and it explains how one species spread across most of a continent.
• Males break the mygalomorph rule by wandering in daylight, often the day after heavy rain. It is high-risk — birds and cars take a heavy toll — and it is the reason most human encounters happen.
• Funnel-web antivenom works on mouse spider envenoming. That cross-reactivity followed from the discovery that the key toxins hit the same sodium channel target.
• Actinopodidae is a Gondwanan family. Missulena in Australia and Actinopus in South America are relicts of a landmass that broke apart long before there was an ocean between them.

In summary, mouse spiders are secretive, long-lived trapdoor hunters that almost nobody would notice if the males did not go walking in the sun. Most bites amount to little, but the venom of at least one species is chemically close to a funnel-web's. Learn the wide-set eyes and short spinnerets, keep your distance, and treat every bite as an ambulance call.