Red-back Spider Latrodectus hasseltii

Identification

The female Red-back Spider is easily recognised because of her distinctive body colours and shape. The body has a characteristically pea-shaped abdomen and the legs are long and slender. The upper side of the abdomen usually has a broad red stripe, while the underneath always has an hourglass-shaped red mark. Juvenile females have white markings on the abdomen. The female’s body is about 10 mm long, excluding the legs.

A female Red-back Spider (black and white illustration)
Illustrator: Graham Milledge / Source: Museum Victoria

The male Red-back Spider is much smaller than the female – only about 4 mm – and it is rarely seen. The body is light brown, with no red markings, but there are white marks on the upperside of the abdomen and a pale hourglass mark underneath.

The Red-back Spider makes a web to catch its prey. It consists of a tangled array of sticky catching lines attached to the surroundings.

A female Red-back Spider at its web
Photographer: Graham Milledge. Source: Museum Victoria

Habitat and biology

This spider is commonly found outdoors around human habitation in such places as rubbish, litter, old tins and containers, under and on steps of the veranda, and on, or under the seats of outdoor toilets. Storage stacks and disused furniture will encourage the breeding of this spider. In nature, it occurs under logs, bark, sides of rocks, etc. As the spider rarely leaves its web, humans are not likely to be bitten unless some part of the body (e.g. the hand) is put into the web.

Always check before moving items that have been stored outdoors for some time. Wear gloves when cleaning up rubbish areas.

The female produces up to 10 pale yellow egg sacs, each with approximately 250 eggs. Females may live for two to three years, and males for about 90 days.

Bites

The bite is highly venomous. It is characterised by intense localised pain around the bite site. Other symptoms may include sweating, muscular weakness, loss of coordination and, in severe cases nausea, vomiting, convulsions, etc. Antivenom is available.

The following description of the signs and symptoms of envenomation is quoted with permission from Australian Animal Toxins, by Struan Sutherland (Oxford University Press, 1983).

‘The normal sequence of events after a bite is as follows. A sharp pin-pricking pain is almost invariable. Usually the bite site becomes hot. Erythema and oedema develop rapidly. Localized sweating often occurs. The swelling is generally limited to an area of several centimetres in radius from the bite site; occasionally it is extreme. Approximately five minutes after the bite, intense local pain commences and increases in severity and distribution. In most cases, pain is the predominant symptom; the patient is sometimes distraught and even hysterical because of its intensity. Movement of the affected limb often significantly increases the pain. About thirty minutes after the bite, pain and swelling are often experienced in the regional lymph nodes. If abdominal pain occurs, it is worse when the lower extremities or genitals were bitten, probably due to lymph node involvement. Sometimes severe pain develops in parts remote from the bite site, for example, in an opposite limb or the opposite side of the trunk.

Uncommon, even bizarre, signs and symptoms have developed in some cases. These include tetanic spasms, tingling in the teeth, swelling of the tongue, bite site infection, convulsions, excessive thirst, severe diarrhoea, anaphylactic reaction to the venom, blotchy rash on face, haemoptysis, dyspnoea, dysuria, severe trismus, persistent anorexia, periorbital oedema and/or conjunctivas. Patchy areas of what was described as “bizarre sweating” are not uncommon.’