The reputation of Australia as a place where spiders reach imposing sizes is true. This notoriety is earned through several species that are physically massive compared to most spiders found elsewhere. While the sheer physical presence of these arachnids often sparks fear, their size does not always correlate with a medical threat to humans. This article explores what defines a “big” spider in Australia and the relationship between size and danger.
Defining Big Spiders
In Australia, a spider is defined as “big” primarily by its leg span, rather than its body mass. Many of the country’s largest spiders have long, slender legs that contribute greatly to their overall diameter. A spider is considered large when its leg span reaches or exceeds the width of a human palm, roughly 10 to 12 centimeters.
The most notable species can reach a diameter equivalent to a small dinner plate, with some individuals occasionally spanning up to 23 centimeters across. While spiders like the South American Goliath Birdeater exceed Australian species in body bulk, Australia’s largest spiders are distinguished by their expansive, long-legged reach. This focus on leg span makes them appear particularly large when seen on a flat surface.
The Most Notorious Giants
The species most responsible for Australia’s large-spider reputation is the Huntsman spider (family Sparassidae). Australian Huntsman spiders, such as the Grey Huntsman (Holconia immanis), reach leg spans of up to 15 centimeters, with some specimens approaching 20 centimeters. They are characterized by long, crab-like legs that splay out sideways and a flattened body that allows them to slip into narrow crevices.
Huntsman spiders are active hunters that stalk prey rather than build webs, and they are fast runners, capable of moving nearly a meter per second. Their notoriety stems from seeking shelter in dark, protected places, often including human dwellings and vehicles. It is common to find them hiding behind curtains, car sun visors, or darting across walls, movements that contribute significantly to the fear they inspire. Other large spiders include Australian tarantulas, which are bulkier but generally more reclusive in their deep, underground burrows.
Size Does Not Equal Danger
Despite their intimidating appearance, the spiders that reach the largest sizes in Australia are generally of low medical risk to humans. The Huntsman spider, while large, is non-aggressive and prefers to flee rather than bite. Bites from these large spiders typically cause only localized pain and swelling, resulting in mild, non-systemic symptoms.
Conversely, the most medically significant spiders in Australia are often much smaller in physical size. The Sydney Funnel-Web spider, one of the most dangerous in the world, has a body length of only 1.5 to 5 centimeters. Similarly, the Redback spider, recognizable by the red stripe on the female’s small, pea-sized body, carries a venom that can cause severe illness. Antivenoms for both the Funnel-Web and Redback have been available for decades, leading to a significant reduction in severe outcomes and no substantiated fatalities since the early 1980s.