atrodectus hasselti is found throughout Australia except in the hot deserts and coldest mountains. It is closely related to the Black Widow spider which is the most common source of spider bites overseas. The only venomous spider in New Zealand, the Katipo, is almost identical to the Red-back.
The female is about 3 times the size of the male and has a spherical satin-black abdomen about 1cm in diameter with a red/orange stripe. The stripe can be pink or even a light grey. The spider has eight long legs sprouting from the tiny front segment of the body.
The bite of the female can be dangerous to humans but no deaths have occurred since antivenene was introduced in 1956. Symptoms of being bitten are severe pain, sweating, particularly in the bite area, muscular weakness, nausea and vomiting.
The bite of the smaller male is considered harmless due to his small jaws being ineffective.
Mum spider is a real nasty, she eats dad after mating. After mating, and dinner, she spins up to 8 round balls of web for her eggs and some of these balls contain as many as 300 eggs. Weather permitting, the eggs will hatch in about 2 weeks time and the spiderlings will moult several times as they grow to full size.
The web is built in dry sheltered areas such as under rocks, in logs, junk-piles, sheds and dunnies. It consists of a funnel shaped retreat area with sticky threads running vertically to ground attachments.
Unlike the Funnelweb, the Red-back is not aggressive but will guard her eggs fiercely or will bite if trapped in clothing or rubbish being collected. Most bites are on the hand or foot of the victim.
There are no recorded cases of people being bitten you-know-where when sitting on a toilet seat.