Invertebrates
Redback Spider
Latrodectus hasselti · also called redback spider
The redback spider is Australia’s version of the black widow, and it lives in exactly the places people don’t want it: sheds, letterboxes, garden pots, and the underside of outdoor furniture. Small, glossy black, and marked with a red stripe, the female builds a strong, messy web with sticky lines anchored to the ground — and a bite from her brings hours of spreading, escalating pain.
Overview
The redback is native throughout Australia, most abundant in and around towns, and has spread by trade to New Zealand, Japan, and elsewhere. The female’s body is about 1 cm, round and jet black with a red back stripe and a red hourglass beneath; the male is only 3–4 mm, brown, and rarely bites. It is a widow spider, in the same genus as the North American black widows.
The bite
The neurotoxic venom causes latrodectism — pain that starts at the bite and spreads over an hour or two, with sweating, nausea, and raised blood pressure, sometimes lasting days. Antivenom has been available since 1956, and despite a couple of thousand bites a year, deaths are now extremely rare.
Living with people
Redbacks favour dry, dark, sheltered spots near the ground, which is why bites so often happen when someone reaches into cluttered outdoor storage or pulls on a glove or shoe a spider has moved into.
The male’s sacrifice
During mating the male somersaults his abdomen onto the female’s fangs, and she frequently begins eating him mid-copulation. Cannibalised males mate longer and father more eggs — a rare case of a male apparently cooperating in his own consumption.
Status
The redback has not been formally assessed. It is abundant in Australia and an established introduction in several warm-climate countries.
Redback Spider: common questions
How dangerous is a redback spider bite?
It is a serious but very rarely fatal bite. The venom produces latrodectism, in which pain begins at the bite site within minutes, then intensifies and spreads over the following hour or two to the limb and beyond, often with sweating, nausea, headache, and raised blood pressure. Without treatment the symptoms can persist and recur for days. Since redback antivenom became available in 1956, deaths have essentially stopped, even though bites are common, because most cases can be managed with pain relief and, when needed, antivenom. Children, the elderly, and anyone with severe symptoms should get medical care promptly.
Where are you most likely to meet a redback?
Around buildings and in gardens rather than out in the bush. Redbacks like dry, dark, undisturbed pockets close to the ground, so they turn up under garden furniture and pot plants, in sheds and garages, inside rolled-up hoses and gloves, in mailboxes and meter boxes, and among stacked timber or bricks. Bites frequently happen when someone puts a hand or foot into one of these spaces, or pulls on gardening gloves or shoes that a spider has moved into, which is why the standard advice is to shake out footwear and check before reaching into cluttered outdoor storage.
How do you tell a redback from a black widow?
They are close relatives and very similar. Both are glossy black with a round abdomen and a red hourglass mark on the underside. The clearest difference is that the female redback almost always has an additional bright red or orange stripe running along the top of the abdomen, whereas most North American black widows are plain black on top. Geography also settles it — redbacks are the widow spider of Australia and a few places it has been introduced, while black widows are American. Their venoms and their effects are broadly similar.
Why does the male redback let itself be eaten?
It appears to be a reproductive strategy. When a male redback mates, he actively flips his abdomen up over the female's mouthparts, positioning himself to be eaten. Males that are cannibalised copulate for longer and fertilise more of the female's eggs, and because males are tiny, short-lived, and unlikely to find a second mate anyway, giving the female a meal that also boosts his own paternity can be worthwhile. It is one of the clearest examples known of a male animal facilitating rather than merely suffering sexual cannibalism.