Arachnologists typically use different metrics to measure size, focusing either on overall mass and body bulk or on the maximum reach of the creature’s legs. This distinction means that a single species rarely holds all the size records simultaneously. Examining the contenders across these various measures helps to clarify which species truly earn the title of largest based on specific criteria.
The Reigning Champion By Mass
The title for the heaviest and most massive spider belongs to the Goliath Bird-eater, Theraphosa blondi. This tarantula can achieve a body length of up to 4.75 inches, but its weight sets it apart from all other known species. Adult females commonly weigh more than 6 ounces. This substantial bulk makes it the champion when size is defined by overall mass or volume.
T. blondi primarily inhabits the rainforests and swampy areas of northern South America, including Brazil, Guyana, and Venezuela. They live in deep, silk-lined burrows, waiting for prey. The spider’s carapace and legs are covered in thick, reddish-brown hair, giving it an imposing appearance.
Despite its common name, the Goliath Bird-eater rarely preys on birds. Its diet is mainly composed of ground-dwelling invertebrates, such as crickets and beetles, and small vertebrates. These include frogs, lizards, and sometimes small rodents, which the spider subdues using its large, up to 0.8-inch long fangs.
When threatened, the Bird-eater employs a unique defense mechanism known as stridulation, where it rubs specialized bristles to produce a loud, hissing sound. A more direct defense involves kicking off thousands of tiny, irritating urticating hairs from its abdomen. These microscopic barbs can cause discomfort and swelling if they contact the skin or eyes.
The Longest Spider By Leg Span
The measurement for maximum leg extension leads to a different champion, the Giant Huntsman spider, Heteropoda maxima. This species can boast a leg span reaching up to 12 inches, which is roughly the size of a dinner plate. Although its legs are extremely long and slender, the actual body of the Giant Huntsman is relatively small and flat compared to the Goliath Bird-eater.
H. maxima was first discovered in 2001, inhabiting the dark, isolated caves of Laos in Southeast Asia. Its flattened body is an adaptation that allows it to easily slip into tight rock crevices, a trait common among many huntsman species. This helps it hide efficiently from predators and serves as an ambush position for hunting.
Unlike the burrowing Goliath, the Giant Huntsman is an active, highly mobile predator that relies on speed to catch prey. It does not spin webs to capture food, instead utilizing its wide stance and rapid movement to ambush insects and other small arthropods. Its impressive width and agility make it a formidable hunter in its subterranean environment.
The Extinct Contender
The paleontological record offers evidence of ancient arachnids that once dwarfed many modern species, although their classification is sometimes complex. One notable contender is Megarachne servinei, a fossil specimen discovered in Argentina that was initially misidentified as a massive, extinct spider. Subsequent, more detailed analysis revealed that this creature was actually a type of extinct water scorpion, or eurypterid, from the Carboniferous period.
However, fossil evidence does confirm the existence of truly enormous ancient spiders, such as the Nephila jurassica. This extinct species of golden orb-weaver was discovered in Inner Mongolia, China, and dates back approximately 165 million years to the Jurassic period. The fossilized female specimen indicates it had a body length of about 1 inch, but a leg span estimated to exceed 6 inches.
While this size is impressive for a web-spinning spider, the fossil record suggests that the maximum size reached by arachnids has fluctuated over geological time. The largest known true spiders from the past were substantial, yet they generally did not surpass the sheer bulk or maximum leg span achieved by the modern living giants.
How Spider Size is Measured
Scientists use three primary metrics to standardize the measurement of spider size, each providing a different dimension of the animal’s physical presence. Body length is the simplest measure, taken from the front of the cephalothorax to the tip of the abdomen, excluding the legs. Leg span is determined by measuring the distance from the tip of the longest leg on one side to the tip of the corresponding leg on the opposite side.
Mass, or weight, is widely considered the most definitive biological measure for determining the overall “biggest” animal, as it quantifies the total volume of living tissue. This measurement is particularly relevant for bulky species like the Goliath Bird-eater, whose weight far surpasses that of other spiders. Accurately measuring the mass of a live, often aggressive specimen presents significant logistical challenges.
The reliance on different measurements explains why separate species hold the records for the largest mass and the longest span. The Goliath Bird-eater earns its title through superior mass, while the Giant Huntsman is recognized for its impressive linear dimension. Understanding these distinct metrics is necessary to properly classify the true scale of the world’s largest arachnids.