The black house spider, Badumna insignis, is one of the more common spiders found around New Zealand homes. Although their bite is quite painful the main concern for homeowners is that they build unsightly, dense webs around windows, doors and eaves. Fortunately, this makes it very easy for the homeowner to carry out their own pest control treatment.
What do black house spiders look like?
Black house spiders are a charcoal / black colour, although the abdomen appears grey (sometimes brownish) with white markings. Their legs can be brown and black. Females can have a body of up to 18mm long with a leg span of 30mm. Males are noticeably smaller and slimmer. Their dense, obvious webs are a key identifying feature, if the spider cannot be located.
Where do black house spiders live?
In their natural environment, black house spiders build their webs on tree trunks, logs and under rocks – any place where there is a crevice to hide. Around buildings, they build their webs around window and door frames, in vents and under eaves.
Black house spider web
Black house spiders build dense webs, often with a funnel-like shape which leads to their hiding place. Their webs are not actually sticky but make up of a dense network of silk, which is designed to snag the spiny legs of insects.
Female spiders will never leave their web unless they are forced to, and will keep on adding layers of silk, making the web denser over time.
Other interesting facts:
Males leave their webs to find females and will pluck strands on the female’s web to make sure she is receptive to mating. The males will often remain with the female for several days and mate several times – they are not consumed after mating as is often the case with some other spiders!
Black house spiders are one of the favourite prey items of white-tailed spiders. So, carrying out a treatment for black house spiders will make your property less attractive to white-tail spiders due to the lack of food.
Black house spider bite
Black house spiders are actually quite timid and will often retreat into their web when disturbed. However, their bite can be quite painful and cause local swelling around the bite area. Nausea, vomiting and sweating has been recorded in a few cases. Although their webs have a funnel-web appearance, it’s important not to confuse the black house spider with a funnel web spider, as following a bite you should follow the standard spider bite first aid, rather than the funnel web spider bite first aid.
Standard spider bite first aid:
- The patient should sit down and try to relax
- Clean the bite with water and disinfectant
- Apply an ice pack to the bite area
- If possible, collect the spider or take a picture for identification (if medical treatment is required)
- If symptoms worsen seek medical attention
Black house spider treatment
A general insecticide spray around the perimeter of the home, particularly around windows and doors, under eaves and in vents, will prevent black house spiders building their webs for many months.
If you already have black house spiders living around the outside of your home, make sure you spray the webs and into their hiding places. Leave the webs in place for at least 24 hours before brushing down the webs. Don’t wash the webs down with a hose, as it will also wash the insecticide away.