Redback Spider

Scientific Name: Latrodectus hasselti

How to identify a redback spider

Redback spiders (Latrodectus hasselti) belong to the Family Theridiidae, which is found worldwide. Female Redback Spiders are black (occasionally brownish) with an obvious orange to red longitudinal stripe on the upper abdomen, with the red stripe sometimes being broken, and an "hourglass" shaped red/orange spot on the underside of the abdomen. Juveniles have additional white markings on the abdomen. Females have a body about the size of a large pea and slender legs. The males' red markings are often less distinct. The body is light brown with white markings on the upper side of the abdomen, and a pale hour-glass marking on the underside.

Where are redback spiders commonly found?

Redback Spider webs consist of a tangled, funnel-like upper retreat area from which vertical, sticky catching threads run to ground attachments. The Redback Spider favours proximity to human habitation, with webs being built in dry, sheltered sites, such as among rocks, in logs, shrubs, junk-piles, sheds, or toilets. Redback Spiders are less common in winter months.

Why are redback spiders considered a pest?

Redback bites occur frequently, particularly over the summer months. More than 250 cases receive antivenom each year, with several milder envenomations probably going unreported. Only the female bite is dangerous. They can cause serious illness and have caused deaths. However, since Redback Spiders rarely leave their webs, humans are not likely to be bitten unless a body part such as a hand is put directly into the web, and because of their small jaws many bites are ineffective. The venom acts directly on the nerves, resulting in release and subsequent depletion of neurotransmitters.

Common early symptoms are pain (which can become severe), sweating (always including local sweating at bite site), muscular weakness, nausea and vomiting. Antivenom is available. No deaths have occurred since its introduction.

Apply an ice pack to the bitten area to relieve pain. Do not apply a pressure bandage (venom movement is slow and pressure worsens pain). Collect the spider for positive identification. Seek medical attention.

What is the biology and lifecycle of a redback spider?

Once the female has mated, she can store sperm and use it over a period of up to two years to lay several batches of eggs. She spends much time producing up to ten round egg sacs (1cm diameter), which are white, weathering to brown over time. Each egg sac contains approximately 250 eggs and only one to three weeks need to pass before more eggs can be laid. These sacs are suspended within the web. Sometimes small ichneumonid wasps parasitise them, puncturing each sac with tiny holes. The young spiderlings hatch in two to four weeks. Spiderlings are cannibalistic and will eat unhatched eggs and other spiderlings. The spiderlings disperse by ballooning to another suitable nest site on long silk threads that are caught by air currents.

Females mature on average in about four months. The smaller male matures on average in about 90 days. Females may live for two to three years, whereas males only live for about six or seven months.

Management Tips for Redback Spider

Other than keeping the perimeter of the property clear of rubbish and vegetation, spraying for redbacks is the best method of control / prevention.

Redbacks tend to build their webs in sheltered dry areas. Target redback nesting areas such as fencing (particularly inside tubular metal fencing), retaining walls, rocks and logs. They can sometimes also be found in roof voids, where it is also warm and dry, so check the roof void each year and treat as required.

General Spider Prevention Tips

• Keeping garden beds and rubbish away from the edge of the house will significantly reduce the spider population.

• If garden beds next to the house are kept in place, it is important to keeping vegetation trimmed back from the edge of the house and paths.

• Make sure insect screens and draft excluders are in good repair and well fitting

• Keep clothes and shoes off the floor to reduce spider hiding places.

General Spider Control Tips

• The best treatment for web-building spiders is to spray their webs and hiding places with an insecticide (ready to use pump back or aerosol). The key tip to get the best performance is to wait a day or two after spraying before brushing down any webs. This ensures the spiders will have picked up a lethal does of insecticide (by walking on the web) and by using a brush (rather than hose), you can ensure the insecticide remains in place to prevent new spiders taking up residence.

• To prevent web-building spiders take up residence in the first place, spraying around doors, windows and vents, as well as under eaves and guttering delivers excellent results. As these spots tend to be sheltered from sun and rain, the treatment can last many months.

• It is a lot more difficult to prevent running spiders entering the home. Carrying out a preventative spray around the perimeter of the home and any openings will have some benefit, although running spiders often walk on the tips of their legs, preventing them from picking up a lethal dose of insecticide. However, if you carry out a preventative treatment for web-building spiders and other insects, the numbers of running spiders will be greatly reduced, as there will be little prey for them to feed on.

• Even with the best control program the occasional spider may get in. A crawling insect aerosol should be kept on hand to spray the occasional unwanted spider. Ensure the spider receives a good dose and keep your distance.