The red-back spider is closely related to the black widow spider of the United States and the katipo of New Zealand. The female red-back is black with a distinctive red or orange marking on its back, although this may sometimes be absent. These markings may be broken into spots in front and, sometimes, thin white lines may be visible. The female can grow up to 15mm long. Males are very small and usually only grow up to 5mm long. The female is the only one capable of harming humans as the male’s fangs are incapable of penetrating human skin. The male is short-lived and has more complex markings than those of the female, incorporating white and sometimes yellow markings.
Red-back spiders can be commonly found in logs or under rocks in the bush as they tend to reside in dark, dry areas. In suburban regions, the red-back has been known to live under roof eaves, floorboards, shelves, flower pots or in garden sheds. The web is a tangle of dry silk. The traplines are sticky to assist with catching their prey.
Red-backs eat almost any small insects that are caught in their webs. They will also eat skinks and even juvenile mice, snakes and frogs. Red-back spiderlings will also eat their siblings. The red-back spider weaves a snare-like structure that traps prey walking on the ground beneath the web. Its spring-like action traps the animal into the small web above, where it cannot escape from the traplines that are covered with sticky globules.
Female red-backs take about 2-3 months to mature and can lay 3-8 egg sacks between September and May. Each sack can contain up to 300 eggs. However, most of the hatchlings do not survive because they are eaten by their siblings and are very prone to wasp parasitism.