Black house spider fact sheet | Field of Mars EEC

What are black house spiders?

Black house spiders are common Australian spiders that often live around rough bark, logs, rocks, fences, window frames, brickwork and wall crevices. They are sometimes called window spiders because they often make their webs around windows and buildings. Their scientific name is Badumna insignis. They are arachnids, which means they have eight legs and two main body parts.

A black house spider.

What do black house spiders look like?

Black house spiders are dark, sturdy spiders. Their legs and front body are usually dark brown to black. Their abdomen is often charcoal grey or black, sometimes with pale markings that can be hard to see. Females are usually larger than males, although adult size can vary.

Black house spiders can be mistaken for funnel-web spiders because their webs have funnel-like entrances. However, black house spiders are not Australian funnel-web spiders. Their exposed lacy web is different from the burrow and trip-line web made by many true funnel-web spiders.

Adult black house spiders have dark legs and a charcoal-grey abdomen with pale markings.

Where do black house spiders live?

Black house spiders live in many parts of Australia, especially southern and eastern Australia, including the Sydney Basin. In bushland, they often use rough-barked trees, logs, rock walls and deep crevices. Around homes and school buildings, they may live near windows, doors, brickwork, fences, eaves and wall gaps.

At Field of Mars Reserve and nearby suburbs, suitable habitat may include rough bark, fallen timber, fences, rock edges and building corners where insects are common and the spider can build a sheltered retreat.

Black house spiders make lacy sheet webs with a funnel-like retreat in sheltered cracks.

In Field of Mars Reserve black house spiders often make lacy webs in sandstone cracks.

What do black house spiders eat?

Black house spiders are predators. They eat insects and other small invertebrates that become caught in their web. In bushland, flies, beetles, butterflies and bees may be attracted to sap or rough bark and become snagged in the fine edges of the web. Around buildings, moths, beetles and termites can be attracted to lights and may fly into black house spider webs.

Moths are one of the flying insects that may become trapped in black house spider webs.

How do black house spiders use silk?

Black house spiders make lacy sheet webs with one or more funnel-like entrances leading into a hidden retreat. Their silk is cribellate silk. This means it is not sticky like some orb-weaver silk, but is made from many fine combed strands that can snag insect legs. Fresh silk can look fine and zigzagged, while old webs can look grey, woolly and messy as new silk is added over time.

In bushland, black house spider webs can spread from a silk-lined hole in bark.

What is the life cycle of a black house spider?

Female black house spiders make several white silk egg sacs inside the web retreat. The female stays with the eggs until they hatch. Young spiderlings later disperse to find places where they can build their own webs. Black house spiders mature during summer and can live for about two years.

A related house spider, Badumna longinqua, with hatchlings. Black house spider spiderlings also hatch from silk egg sacs hidden inside the web retreat.

What adaptations do black house spiders have to help them survive?

Black house spiders have many adaptations that help them survive. Their dark body helps them hide in shadowy cracks, bark and wall crevices. Their lacy web catches insects without the spider needing to chase them. Their hidden retreat helps protect them from predators and weather. Fine hairs and sensitive legs help them detect vibrations when prey touches the web.

Their behaviour is also an adaptation. Females usually stay close to their web and repair it again and again, rather than moving often. This helps them keep a safe shelter and a reliable feeding place.

A black house spider waits close to its web retreat, ready to detect vibrations in the silk.

Why are black house spiders important?

Black house spiders are important predators in food webs. They help control insects such as moths, beetles, flies and termites. They are also food for other animals, including birds, white-tailed spiders and some parasitic wasps and flies.

Although their webs can look messy around buildings, these spiders are part of the natural pest-control system in gardens, bushland edges and urban areas.

Black house spiders help control insects around buildings, gardens and bushland edges.

How can you help black house spiders?

You can help black house spiders by protecting natural habitat such as rough bark, logs, rocks and leaf litter. These places provide shelter for spiders and the small animals they eat. In gardens, avoid unnecessary pesticide use because pesticides can harm spiders and many other invertebrates.

If you find a black house spider, leave it where it is if it is not causing a problem. Watch from a safe distance, take a photo if you can do so safely, and avoid breaking its web.

Black house spiders are best observed from a safe distance and left undisturbed.

Related fact sheets

More invertebrate fact sheets

• Invertebrate fact sheets – overview
• Arachnids fact sheet – explains the main features of spiders and other arachnids.
• Net-casting spider fact sheet – another spider that uses silk in a specialised way.
• Huntsman spider fact sheet – another common Australian spider found around homes and bushland.
• St Andrew’s Cross spider fact sheet – a web-building spider found in gardens and bushland.

Habitats and ecosystems

• Tree habitats fact sheet – explains how bark and tree trunks provide shelter for spiders and other animals.

• Rock and log habitats fact sheet – explains how logs and rocks provide shelter for invertebrates.

• Eucalypt forest fact sheet– explains the local bushland habitat at Field of Mars Reserve.

• Field of Mars Reserve fact sheet – explains the reserve habitats that may support black house spiders and other invertebrates.

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