Redback Spiders: How to Identify Them and Prevent Bites

Australia’s Redback spiders (Latrodectus hasselti) look like North America’s Black widow spiders (Latrodectusmactans). Indeed, these spiders are called redback black widow spiders, but it is a distinct species and only native to Australia.

Redback spiders are found throughout Australia and are common in urban settings and areas where construction and human activities have removed topsoil and vegetation.

During the summer, redback spiders are responsible for hundreds of bites of humans.

How to identify redback spiders.

Adult female redback spiders are black or brown and have an hourglass-shaped red or orangish mark on the underside of their abdomen and a conspicuous red stripe on the upper side. Her spherical body may be as much as 2/5ths of an inch long.

Male redback spiders are brown with white markings on the top of their abdomen and lighter-toned and less definite red markings. Males have bodies about 1/10 of an inch long.

Juvenile redback spiders are grayish with dark spots, and the young spiders grow darker with each mount. In addition, young female redback spiders have extra white markings on their abdomens.

Redback spiders: Webs and habitat.

The web of a redback spider is an embarrassing mess. The web appears as if the spider waited until the last second and just threw something together. No two redback spider webs look alike, but they all contain an upper funnel for the spider to retreat into when disturbed or waiting for prey, and all have sticky catch threads that await game traveling on the ground.

Redback spiders thrive in proximity to human residences and commercial structures. They construct the haphazard-looking webs in dry wind-sheltered areas such as wood piles, rockeries, sheds, garages, and behind toilet seats.

If enough prey is available, there are few places in Australia redback spiders won’t settle down.

Redback spiders: Diet.

Redback spiders eat small invertebrates such as flies, woodlice, moths, beetles, and cockroaches; there are reports of redback spiders preying on larger venomous invertebrates, including centipedes, certain trapdoor spiders, and even funnel-web spiders, lizards, and mice.

How long can redback spiders go without food?

Redback spiders can live without food and still be likely to survive for as long as two months if the temperature remains between 60-68 degrees Fahrenheit.

According to the New ZealandJoumal of Zoology, 1989, Vol. 16, after nine weeks of starvation, redback spiders become too weak to maintain their webs actively and are likely to die if unable to secure prey.

They describe the end stages Of starvation for redback spiders thusly:

“Stage IV. Abdomen greatly shrunken, wrinkles extend over much of body surface. Red markings faint, abdomen dull. Spider inactive, markedly sluggish. Web-building nil. Mortality highly likely.

Approximate period of starvation: 9-12 weeks.”

“Stage V. Abdomen collapsed, wrinkles widespread Red markings very faint. Sluggishness pronounced, spider inactive. Legs drawn into body, little or no movement if prodded. Spider grounded, not in web. Mortality certain. Approximate period of starvation: 10-14 weeks.”

Redback spider mating habits.

The Latin meaning of the word Latrodectus is “biting in secret.” And for male redback spiders, that is what their female mates do to them. Indeed, most males do not survive the breeding process.

Male redback spiders don’t live in or produce webs. Instead, they are lured through chemical attraction to the webs of available and ready females during the summer breeding season.

Because the male redback spider can never be too sure the female is 100% for him, he must use extreme caution when approaching her or her web—lest he is mistaken for a meal.

Even a ready-to-mate female is hard to get close to, so male redback spiders offer their abdomen to keep the female’s attention. Then, while he is sticking his first sperm-soaked palp into the reproductive opening in her abdomen, he is injected with digestive juices.

If the male redback spider has enough life left in him, he will attempt to place his second palp in her—all while being dissolved and prepared for digestion by his mate.

Only the redback spider female consistently consumes her mate while breeding.

Redback spiders: Lifecycle.

A mated female can store male sperm for two years and use it to lay several batches of eggs. These eggs are stored in an egg sac she creates from her spinnerets and contains 200-300 eggs. A female redback spider can produce as many as ten egg sacs and up to 3,000 spiderlings during her lifespan.

Redback spider eggs take 15-30 days to hatch, and the hatchlings often feed on each other and any unmatched eggs they find.

Female redback spiders mature in 120 days and can live for up to three years. Males have significantly shorter lifespans, with about six months being the average.

Redback spider bites.

Redback spiders frequently bite humans during the summer. Of the sexes, only the female’s bite is dangerous, and with an anti-venom available for decades, death is unlikely.

Since female redback spiders rarely leave their webs, most bites occur when humans place their hands in the webs and threaten the spider.

Redback spider bites cause extreme pain, muscle weakness, vomiting, nausea, and sweating 9especially at the site of the wound).

Administer first aid. Apply a cold compress to the bite location, collect the spider in a clear container if possible (to facilitate identification and treatment), and get medical attention.