The fascination with the largest spiders on Earth often begins with a simple question about size, but the answer is complex. The definition of “biggest” depends entirely on the metric used to measure the animal. Scientists typically use two distinct measurements to classify these giants: mass and leg span, which results in two different record holders. This distinction is necessary because a heavy, bulky spider may have a shorter reach than a lighter, more slender species.
The Record Holder by Mass: Goliath Bird-Eater
The title for the world’s heaviest spider belongs to the Goliath Bird-Eater, scientifically known as Theraphosa blondi. This tarantula is a true heavyweight, with an average weight reaching up to 175 grams. Its immense size is characterized by a robust, bulky body, which can measure up to 13 centimeters (5.1 inches) in length.
The Goliath Bird-Eater is formidable, covered in dense, reddish-brown or dark russet hairs, giving it a velvety look. Its thick, powerful legs contribute to a leg span that can reach up to 30 centimeters (12 inches). However, its impressive mass is the defining factor, setting it apart as the world’s largest by sheer bulk.
The spider is a member of the tarantula family, Theraphosidae, and possesses fangs that can be up to 3 centimeters (over an inch) long. When threatened, it can perform a defensive display by rubbing bristles on its legs to create a loud, audible hissing sound called stridulation. This species is found in the Amazonian rainforests, where its immense size makes it one of the most imposing invertebrates in its environment.
The Record Holder by Leg Span: Giant Huntsman
The spider that holds the record for the greatest leg span is the Giant Huntsman, or Heteropoda maxima. This species boasts an extraordinary reach, with legs stretching up to 30 centimeters (12 inches) across. Despite this massive diameter, the Giant Huntsman is a comparatively slender animal, with a body length of only about 4.6 centimeters (1.8 inches).
This slenderness means it is significantly lighter than the Goliath Bird-Eater. The Giant Huntsman is characterized by its long, spindly legs that splay out in a crab-like fashion, typical of the Sparassidae family. Its coloration is usually a pale yellowish-brown, and its flattened body allows it to squeeze into narrow crevices.
The species was first formally described in 2001, after being discovered in a cave in Laos, Southeast Asia. The relatively recent discovery of such a large creature surprised the scientific community. Its long legs and speed are adaptations for its hunting style, which relies on active pursuit rather than web-building.
Defining Size: Measuring Spiders
The scientific methodology for determining a spider’s size relies on two distinct metrics, which explains why two different species hold the “biggest” title. The first measurement, mass, is determined by accurately weighing the specimen, typically measured in grams. Mass directly reflects the spider’s overall bulk and volume, making it the most objective measure of true “heaviness.”
The second primary metric is leg span, which measures the distance from the tip of the longest leg on one side to the tip of the longest leg on the opposite side, with the legs stretched out. This measurement captures the spider’s total reach and diameter. Leg span gives a dramatic, visually impressive size, but it can be misleading since a spider with long legs will have a huge span but little mass. Body length, measured from the front of the cephalothorax to the end of the abdomen, is also used as a metric independent of the legs.
Where These Giants Roam and What They Eat
The two largest spiders inhabit vastly different ecosystems, each with hunting strategies tailored to their environment. The Goliath Bird-Eater is native to the humid rainforests of northern South America, with populations found across Venezuela, Guyana, and northern Brazil. This tarantula is a terrestrial species, living in silk-lined burrows beneath the forest floor.
Despite its common name, the Goliath Bird-Eater rarely preys on birds. Its diet consists mainly of invertebrates such as earthworms and large insects. It is an opportunistic nocturnal hunter, ambushing small terrestrial vertebrates like frogs, lizards, and rodents. Once the prey is secured, the spider uses its large fangs to inject venom, which liquefies the internal tissues for consumption.
In contrast, the Giant Huntsman lives thousands of miles away in Laos, where it is often found in caves and surrounding forest areas. This species is an active hunter that relies on exceptional speed to pursue and capture its prey, rather than spinning a web. Its diet is composed of insects, small rodents, and reptiles, which it subdues with venom. The Huntsman’s flattened body allows it to maneuver easily through tight spaces, adapting perfectly for a life of speed and stealth.