Redback spider

The redback spider, known scientifically as Latrodectus hasselti, is a highly venomous arachnid.

It is a member of the cosmopolitan genus Latrodectus, which includes the widow spiders. While it is believed to have originated in Australia, it has spread to many other regions. You can now find these spiders in Southeast Asia, Japan, and New Zealand. They have even been found in packing crates in the United States.

Because they often live in warm, sheltered spots near human homes, they are a significant species for medical study.

An adult female redback is very easy to recognize by her physical features. She has a spherical, deep black abdomen that may sometimes appear brownish. A prominent red or orange stripe runs along the dorsal aspect, which is the upper side of her body. On her underside, she displays a bright red or orange hourglass-shaped streak.

The male is much smaller than the female and looks quite different. He is light brown with white markings on the upper side of his abdomen. Female bodies are typically around 10 millimeters long, while males are significantly smaller.

The female builds a specific type of web called a gum-footed tangle web. This web is an irregular tangle of fine, strong silk threads. Some threads are placed strategically to act as trip wires to alert the spider to prey. These vertical strands run to ground attachments and snare animals. If a victim thrashes, weaker horizontal strands called guy lines may break. This action can actually haul the prey into the air. The spider usually stays in a funnel-like retreat area at the back of the web.

Catching prey involves a very specific, step-by-step biological process. First, the spider advances to about one leg's length from the target. She squirts a liquid, glutinous silk from her spinnerets to immobilize the victim. This substance acts much like superglue, sticking the prey's limbs to its own body. The redback then bites the victim repeatedly on the head, body, and leg segments. She injects a complex venom through her two fangs. This venom liquefies the insides of the prey. Finally, the spider hauls the victim to her retreat and sucks out the liquefied contents.

This process can take anywhere from 5 to 20 minutes.

Redback spiders have a complex life cycle and unique reproductive habits. After mating, the female stores sperm in specialized organs called spermathecae. She can use this stored sperm to fertilize several clutches of eggs up to two years later. Each clutch contains an average of 250 eggs housed in a round, white silken sac. Spiderlings hatch about 8 days after the eggs are laid. They may stay inside the sac for a week to feed on yolk. Females can live for two to three years, while males live only six to seven months.

The history of studying the redback involves many different scientists. Swedish arachnologist Tamerlan Thorell first described the species in 1870. He collected specimens from Rockhampton and Bowen in central Queensland. He named the species Latrodectus hasseltii to honor his colleague, A.W.M. van Hasselt. In 1959, arachnologist Herbert Walter Levi revised how we classify these spiders. He focused on the morphology, or physical shape, of female sexual organs. He originally reclassified the redback as a subspecies of the North American black widow. However, modern genetic studies have since confirmed the redback as a distinct species.

Redback venom is primarily neurotoxic to vertebrates, meaning it affects the nervous system. In humans, this can cause a condition called latrodectism. This syndrome often begins with severe pain around the bite site. The pain typically progresses up the bitten limb and can last for over 24 hours. Some people may experience localized sweating, nausea, vomiting, headache, or agitation. Because of the medical importance of these bites, an antivenom has been available since 1956. This makes the redback one of the few spider species that can be seriously harmful to humans.