Mouse Spiders

Introduction

Mouse spiders, Missulena sp., vary from 10 mm - 35 mm body length and all have distinctively bulbous head and jaw regions. They are often confused with funnel-web spiders. While mouse spider bites are not common, a few have caused serious effects in humans, with symptoms similar to funnel-web spider envenomation. Fortunately, mouse spiders are not usually abundant in heavily populated urban areas.

Identification

Mouse spiders are stout black spiders.

Depending on the species, their abdomen is uniform black or dark blue, or black with a light grey to white patch on top.

The head is very wide, shiny, and black, sometimes with bright red or orange-red jaws (chelicerae) and eye region.

The legs are dark and may appear long and thin.

Females are larger, stockier, more solid spider than the males, with a uniform black cephalothorax (fused head and thorax) and body.

• Mouse spiders have high, bulbous heads and jaws
• The carapace is smooth and shiny
• The eyes are spread across the front of the carapace, not closely grouped
• The spinnerets are short, the last segment domed and button-like
• Male spiders have long slender pedipalps
• Male spiders have no mating spurs on the legs
• Males of some species have distinctive colour markings but others are black overall

The following key features distinguish the mouse spiders from other large black spiders:

• bulbous head and jaws
• shiny carapace
• eyes spread across front of carapace
• short spinnerets

Distribution

Mouse spiders are found over much of mainland Australia, in habitats ranging from open forest to semi-arid shrubland.

The species with the largest distribution is the Red-headed Mouse Spider. This may be related to the fact that the spiderlings of this species are known to disperse aerially by ballooning, possibly over many kilometres. This is a very rare ability among mygalomorph spiders, most of which disperse over relatively short distances by walking.

Habitat

Varied owing to the wide distribution range.

The burrows built by the big inland Red-headed Mouse spiders are large, silk-lined burrows that vary from 20 cm to 55 cm deep and are widest in the entrance and bottom chamber areas. A side chamber extends off the main burrow shaft, usually closed by a trapdoor. It provides a refuge from predators and a safe place for the egg sac and spiderlings.

The burrow's most unusual feature are the two surface trapdoors set almost at right angles to each other. The silk and soil trapdoors often merge well with the ground, making them hard to see (and increasing the impression of scattered rather than aggregated burrow sites, making accurate estimates of their abundance difficult). They may be thin and wafer-like or thick and plug-like. Having two doors probably increases both prey catching area and efficiency. A few silk triplines may extend outwards from the entrances. These can help alert the spider to approaching prey or male spiders and also help with surface navigation while hunting.

Little is known about the burrows of other species. The forest dwelling Eastern Mouse Spider appears to have a single, flap-like door and a shallow burrow with a side chamber. Unlike other species, this mouse spider has occasionally been reported living in large aggregations. Recently, almost 300 specimens were collected from the backyard of a house on the central coast of New South Wales after flooding rains drove the animals from their burrows.

Seasonality

The males are often encountered when they wander searching for females from late summer until April-May. They often fall into suburban swimming pools.

Feeding and diet

Insects are the main prey of mouse spiders but their diet could possibly include small vertebrates and other spiders. Prey is usually ambushed from within the safety of the trapdoor 'hides', but mouse spiders have been observed foraging outside the burrow at night. With their powerful jaws and venom, they can tackle prey ranging from ants, beetles and spiders to small lizards and frogs.

Feeding habits

The chelicerae, with the fangs at the end, are the jaws of the spider. As with all modern spiders the mouse spiders jaws move in and out sideways rather than the straight up and down movement of the ancient group of spiders.

Breeding behaviours

Males reach sexually maturity at about 4 years of age. They leave their burrows during the breeding season to find a mate. The mating usually takes place in the females burrow

Most male mygalomorph spiders wander by night in search of females during their mating season. This is to avoid both day-active predators and excessive heat and water loss.

However, the males of several mouse spider species can be seen wandering about by day during the late summer to early winter months (especially after rain).

These daytime wanderers are unique in having distinctive body colour patterns.

Eastern Mouse Spider males (Missulena bradleyi) from eastern Australia have a blue/white patch on the front of the abdomen.

In M. pruinosa from northern Australia, this patch is yellowish-cream and spreads over much of the abdomen. These spiders live in open forest habitats where their pale blue and yellow/cream patches may help them blend in with the dappled shading of the forest floor, perhaps making them difficult for predators to see.

Most arresting are the males of the Red-headed Mouse Spider (M. occatoria) which ranges across semi-arid Australia. These males have a bright reddish-orange head and jaw region and the abdomen has a gunmetal blue tinge. In open woodland and shrubland habitats this pattern may act as both warning and disruptive colouration, deterring some predators and avoiding others by blending in with the sharply shadowed soil and litter background.

By contrast, little is known about the wandering behaviour of some small, forest dwelling mouse spider species that are entirely black in colour.

While wandering, male mouse spiders hold their long pedipalps (carrying the mating organs) extended forwards, presumably seeking an airborne scent (pheromone) associated with the female or its burrow. Once the burrow vicinity is reached the male taps the ground and silk around the doors until the female emerges. If she is receptive the male follows her into the burrow where mating occurs.

Danger to humans

Some mouse spiders have a very toxic venom which is potentially as dangerous as that of the Sydney Funnel-web Spider. However, few cases of serious envenomation have been reported. Unlike funnel-web spiders, the mouse spider is believed to use less venom and possibly even "dry bite".

Although the males are often sighted, bites by Red-headed Mouse Spiders are rare, probably because the spiders occur in less densely populated areas.

Because of their potential toxicity to humans, first aid treatment should be provided as recommended for funnel-web spider envenomation. Fortunately, funnel-web spider antivenom has proven effective in cases of mouse spider bite.