Redback Spiders
Redbacks are Australia's best-known spider. They appear in songs and even have a beer named after them.
Redbacks live all over Australia but are less common in colder regions like Tasmania. They thrive in populated areas. Hundreds of bites are reported each year but less than 30 percent require antivenom treatment. Before an antivenom was available, Redback bites caused about a dozen known deaths. Only female Redbacks usually bite people - the males are generally too small.
Identifying Redback Spiders
- Black to brown pea-sized spiders with a median scarlet-red to orange-yellow stripe on the back of the abdomen.
- The stripe is often broken and outlined with fine white markings
- Slender black-brown legs
- Characteristic orange-red ' hour-glass' shaped marking underneath the abdomen
Juvenile spiders have a more elaborate pattern including lateral stripes - this type of pattern is occasionally retained in adult females. Redback spiderlings are coloured white and black, but with each moult the black pigmentation increases and the red stripe gradually gets larger. The tiny males mature quickly and retain the early juvenile colour pattern. They are only about 3 mm in body length and are not dangerous. Female are up to12 mm body length.
Suspects gallery
Spiders in the genus Steatoda, the cupboard or brown house spiders, are sometimes referred to as 'black redbacks'. Females are similarly sized, but are slightly more stocky spiders than the Redback Spider. They lack any red colouring (although a little is present on some males), but their black to dark brown bodies usually have a few white markings. However, recent observations indicate that their bite can be very painful, with symptoms similar to those of Redback Spider bite (but without the dangerous effects). These are quite common spiders in southern Australia, but their bites seem far less common than those of Redbacks.
Where Redbacks live
Redback Spiders (Latrodectus hasselti) range from India to Indonesia, the Phillipines, New Caledonia and Australia. However, it is possible that more than one species of Latrodectus is represented within this range.
Redback relatives
Redback Spiders belong to the genus Latrodectus or widow spiders. Australia has another widow spider, the Brown Widow Spider (L. geometricus), a circum-tropical species that is found in northern Australia. Its bites are not frequent or severe. There are many widow spider species worldwide including the infamous Black Widow Spider, L. mactans, of America. Others include the Russian Karakurt, European Malmignatte, South Africa's Koppie Spider and New Zealand's Night Stinger. While their colour patterns vary, most species retain the characteristic reddish marking under the abdomen.
Home is where the food is
Redback Spider webs consist of a funnel-like retreat in the upper part of a tangled silk network, from which many vertical, catching lines run down to ground attachments. The lower part of each catching line is adorned with droplets of sticky silk. The upper web is usually built in a sheltered area away from sunlight, while the sticky catching lines run down into more exposed ground areas. Insects, spiders, even small lizards that walk into the 'forest' of sticky lines are held by them while the spider races down, sometimes delivering a quick bite before covering the struggling prey in bands of sticky silk. These swathing silk bands are rapidly thrown out from enlarged spigots on the spinnerets by a row of 'comb-like' bristles on the ends of the last legs, hence the family name, 'comb-footed spiders'.
Seasoned travellers
Redbacks and their egg sacs are easily transported around Australia on trucks and among goods. They have also spread overseas, probably mainly on cargo ships. A few years ago a major infestation was found in the street drainage system and cemeteries of Osaka in Japan. A few imported spiders (or more likely egg sacs and spiderlings), shipped from Australia in a cargo of timber, managed to survive the rigours of Osaka's winter in these relatively sheltered habitats and became well-established.
Redback Spider bites
Redback Spiders are common in the spring and summer months. About 600 bites are recorded each year in Australia. Some result in serious pain and illness, requiring antivenom treatment. However, because of the female Redback's relatively small jaws many bites are ineffective. The male is much smaller and bites are rare, the tiny jaws having difficulty in even penetrating human skin. The two recorded bites had only minor effects.
Antivenom and first aid
An effective antivenom is widely available. No deaths have occurred since its introduction almost 50 years ago.
Pressure bandaging is not recommended for Redback bite as this can aggravate the pain. Instead, cold packs or cold water may help relieve pain. Because the venom molecules are large, they can take some hours to be transported from the bitten area via the lymphatic system and into the blood stream. Medical attention should be sought if a bite is suspected.
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Redback Spider, Latrodectus hasselti View full size
Mike Gray
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