Black House Spider

Black House Spiders are common in urban areas where they often make webs around window frames, earning them the common name of Window Spiders.

Identification

The Black House Spider belongs to the family Desidae. Related species are found throughout Australia.

The Black House Spider (Badumna insignis) is a dark robust spider, with grey hairs usually visible on the carapace. Females are larger than males but there is a great range in adult sizes. The carapace and legs are dark brown to black, and the abdomen is charcoal grey with a dorsal pattern of white markings (sometimes indistinct).

The web structure includes one or more 'funnel-like' entrances to the spider’s retreat, which is sometimes misunderstood as a Funnel-web Spider web. However, Black House Spiders are not at all related to Australian funnel-webs, nor similar in appearance, size or life history. The retreat of a true Australian Funnel-web Spider (famiy Atracidae) is usually less funnel-like and is often a burrow in the ground. Common Southern Tree Funnel-webs make burrows in tree-trunk crevices in similar habitats to Black House Spiders, but their crescent-shaped web entrances are disguised with detritus (eg, bark) particles embedded in the silk, whereas the silk of Badumna webs is exposed.

Habitat

Black House Spiders are found on tree trunks, logs, rock walls and buildings (in window frames, wall crevices, etc). Whilst juvenile spiders may be quite exposed, the ones that survive to adulthood have usually acquired a secure retreat beneath bark or in a deep crevice.

Distribution

Black House Spiders are widely distributed, particularly in southern and eastern Australia.

Feeding and diet

In the bush, Badumna insignis is found especially upon rough-barked trees which provide good shelter for their retreats amongst the cracks in the bark. Trees that have been attacked by wood-boring insects are particularly attractive, as the sap flowing from the bored holes attracts potential prey such as flies, beetles, butterflies and bees, which may become snagged in the fine edges of the web. Around houses, Black House Spiders feed upon insects such as moths, beetles and termites which are attracted to the light of windows and lamps at night.

Life history cycle

The female constructs several white silk egg sacs, which are secured within the web retreat. The female stays with the eggs until they hatch. The spiderlings then disperse. The spiders mature during summertime and live for about two years.

Breeding behaviours

The female spider never leaves her web unless forced to, but keeps on adding new layers - old webs can look grey and woolly from constant additions of silk. Males, when ready to mate, go in search of females in their webs. The male plucks the web of the female to attract her attention. Once the male has made sure that the female will be receptive, he can safely approach and inseminate her with sperm stored in his palps. They may then stay together for several days and may mate again several times. If a small male is caught in a female’s retreat when a larger male enters he can be severely injured and lose several legs.

Other behaviours

The webs of Black House Spiders are constructed from cribellate silk, which is not sticky but is made from multiple combed fine strands and is extremely efficient at snagging the spiny legs of insects. The webs are in the form of lacy silk sheets, which spread out around one or more entrances to the spider’s retreat. New silk is fine and laid in a distinctive zig-zag pattern, but old sheets become matted and untidy. New silk is mostly laid at night.

Predators

Enemies include the White-tailed Spider, as well as parasitic wasps and flies.

Danger to humans

Black House Spiders are timid animals and bites from them are infrequent. The bite may be quite painful and cause local swelling. Symptoms such as nausea, vomiting, sweating and giddiness are occasionally recorded. In a few cases skin lesions have developed after multiple bites.

A cold pack may relieve local pain. Seek medical attention if symptoms persist.

References

• Brunet, B. 2008. Spider Watch: A guide to Australian spiders. Reed New Holland.
• York Main, B. 1976. Spiders. Australian Naturalist Library, Sydney.