Goliath Birdeater (Theraphosa blondi): The Biggest Spider by Mass

What does a Goliath birdeater look like?

The Goliath birdeater is a heavy-bodied, hairy spider in light to dark brown, often with a golden or reddish sheen to its hairs. Its legs are thick and covered in long bristles, and the faint markings on them are much less colorful than in many smaller tarantulas. Like other spiders, its body has two main parts: the front section, or cephalothorax, which carries the legs, eyes and jaws, and the round abdomen behind it.

It has eight small eyes clustered on a bump at the front of the head, but its eyesight is poor. It relies instead on touch, sensing vibrations and air movements through the thousands of fine hairs on its legs and body. Beneath the head are the chelicerae, the spider’s jaws, each ending in a curved fang that can be more than 2 cm (0.8 in) long in large adults. Like other tarantulas, it strikes downward with its fangs rather than pinching them together sideways.

Males have longer, slimmer legs, while females are heavier and have larger abdomens. Unusually, adult males lack the hooks, called tibial spurs, that the males of most tarantulas use to hold the female’s fangs during mating.

How big is the Goliath birdeater?

The Goliath birdeater is the largest spider by mass and by body length. The record weight is about 175 g (6.2 oz), heavier than a baseball, and the body can reach about 13 cm (5.1 in) long. The leg span, measured from the tip of a front leg to the tip of the opposite back leg, reaches about 28–30 cm (11–12 in), roughly the size of a dinner plate.

Two other spiders come close. The giant huntsman spider of Laos has a similar or slightly larger leg span, about 30 cm (12 in), but a far smaller and lighter body. The Goliath birdeater’s closest relatives, the pinkfoot Goliath (Theraphosa apophysis) and the burgundy Goliath (Theraphosa stirmi), are also enormous, and the pinkfoot Goliath may have slightly longer legs. Many record figures come from well-fed spiders in captivity, and wild adults are usually smaller. See how the Goliath birdeater compares with other giants in our list of the largest spiders in the world.

Habitat and range

The Goliath birdeater lives in rainforests of northern South America: Guyana, Suriname, French Guiana, southern Venezuela and northern Brazil. Much of this area lies on the Guiana Shield, an ancient, heavily forested region of rock and uplands. It lives on the forest floor, often in damp, marshy or swampy areas.

It spends most of its life in a deep burrow in the soil, lined with silk to strengthen the walls. The silk also helps the spider climb in and out and feel the vibrations of animals passing nearby. Goliath birdeaters are nocturnal. They usually wait at or near the burrow entrance after dark and rarely wander far, except for adult males searching for mates.

The genus Theraphosa has been revised several times. Some records of “Goliath birdeaters” from the edges of this area may refer to its close relatives, so the exact limits of the species’ range are still being worked out.

What do Goliath birdeaters eat?

Goliath birdeaters are ambush predators. They do not build webs to catch food. Instead, they wait at the burrow mouth, sense prey through vibrations, then rush out, seize it with their legs and fangs and inject venom. They carry the prey back into the burrow, where digestive juices turn its soft parts to liquid that the spider sucks up.

Most of their food is large invertebrates, especially earthworms, beetles, crickets, cockroaches, millipedes and other spiders. Being so large, they can also overpower small vertebrates, and in the wild they have been seen eating frogs, toads, lizards, snakes and small rodents. Birds are taken only very rarely. The story behind the name is told in do Goliath birdeaters eat birds?

Hissing, hairs and other defenses

When threatened, a Goliath birdeater puts on an impressive display. It rears up on its back legs, raises its front legs and shows its fangs. At the same time, it rubs special bristles on its legs and mouthparts against each other to make a loud hissing sound, a behavior called stridulation. Few spiders can make a sound that people hear so easily.

Its main defensive weapon, though, is its hair. The abdomen is covered with urticating hairs, tiny barbed bristles that the spider scrapes off with its back legs and flicks into the air toward an attacker. These hairs irritate skin, eyes and the lining of the nose and throat, and those of the Goliath birdeater are known to be especially irritating. Areas where the hairs have been used turn bald until the spider molts, when they are replaced. If the display fails, the spider may finally bite.

Is the Goliath birdeater dangerous to people?

Not seriously. Its venom is used to subdue small prey and is weak to humans; a bite is usually compared to a wasp sting, with local pain and swelling caused largely by the size of the fangs. Many defensive bites are “dry”, with little or no venom injected. No human death from this species has been recorded.

The urticating hairs cause more problems, especially if they get into the eyes, where they can cause lasting irritation. The best approach is to leave the spider alone, and anyone with a severe reaction after contact with any spider should seek emergency medical help immediately (911 in the US, 112 in the EU, 999 in the UK). How tarantula venom and hairs affect people is explained in are tarantulas dangerous?

Reproduction and life cycle

When a male matures, he weaves a small sheet of silk, called a sperm web, deposits a drop of sperm on it and draws the sperm up into the tips of his pedipalps, the leg-like appendages beside the jaws. He then leaves his burrow to search for a female, finding her by touch and chemical cues. Courtship involves drumming and tapping signals. Unlike in some spiders, the female rarely eats the male after mating.

Some weeks or months later, the female spins an egg sac in her burrow containing around 100 to 200 eggs and guards it closely. The spiderlings hatch after about six to eight weeks and soon disperse to dig burrows of their own.

Young spiders grow by molting, shedding their entire exoskeleton, including the lining of the mouth and lungs, many times. Females take roughly three to six years to mature and keep molting about once a year as adults, which allows them to replace lost hairs and even regrow lost legs. The process is described in how do tarantulas molt?

How long do Goliath birdeaters live?

Females are long-lived, reaching about 15 to 25 years, figures known mostly from spiders kept in captivity. Males have much shorter lives: they mature at about three to six years old, stop molting and usually die within months of reaching adulthood, often after mating. This pattern is typical of tarantulas, as explained in how long do tarantulas live?

Predators and threats

Even a giant spider has enemies. Tarantula hawks, large wasps of the genus Pepsis, sting tarantulas to paralyze them and lay an egg on the body as food for their larva. Coatis, opossums, snakes and some birds also eat large tarantulas, especially young ones and wandering males.

The Goliath birdeater has not been assessed for the IUCN Red List, so its status is Not Evaluated. It lives in large areas of relatively intact rainforest, but deforestation, mining and collection for the pet trade are possible local threats.

Myths and facts

Myth: Goliath birdeaters regularly hunt birds. Fact: Birds are a rare and opportunistic catch. The bulk of the diet is earthworms, insects and other invertebrates.

Myth: A Goliath birdeater bite can kill a person. Fact: The venom is weak to humans. A bite hurts, mostly because of the size of the fangs, but no deaths have been recorded.

Myth: Prehistoric spiders were far bigger than the Goliath birdeater. Fact: Not as far as the fossil record shows. A fossil from Argentina once described as a giant spider, Megarachne, turned out in 2005 to be a sea scorpion, and the largest known fossil spiders had bodies only about 2.5 cm (1 in) long.

Myth: Big spiders are aggressive. Fact: Goliath birdeaters avoid people when they can. They warn with hissing and a raised-leg display, and bite only when cornered or handled.

Goliath birdeaters and people

The name “birdeater” goes back to the German naturalist and artist Maria Sibylla Merian, who visited Suriname and in 1705 published an engraving of a large spider eating a hummingbird. Large tarantulas have been called “bird-eating spiders” ever since. The Goliath birdeater itself was scientifically described in 1804 by the French zoologist Pierre André Latreille.

In parts of northeastern South America, Indigenous people catch and eat Goliath birdeaters, first singeing off the irritating hairs and then roasting the spider in leaves; the taste is often likened to shrimp. Elsewhere, the species is a popular attraction in zoos and insect houses, where visitors can see the world’s heaviest spider safely behind glass.