Goliath Birdeater

The goliath birdeater is the heaviest spider on Earth — a rainforest tarantula the size of a dinner plate, with fangs long enough to draw blood and a defence system that fires clouds of barbed hairs. It is also, for all that, a shy burrow-dweller that would rather not meet you.

Overview

Goliath birdeaters live in the humid lowland rainforests of northern South America, in and around deep burrows they dig in soft, damp ground or take over from rodents. They are nocturnal ambush predators, sitting at or just inside the burrow mouth and rushing out when vibrations tell them something edible has come close.

Physical characteristics

By leg span the goliath birdeater is rivalled by the giant huntsman spider, but by mass nothing comes close: a large female can weigh 175 g, as much as a small apple, with a body 12 cm long and a leg span approaching 30 cm.

The body is covered in dense russet-brown hair. Two fangs, each about 2 cm long, fold down from the front of the head to deliver venom and grip prey. Eight small eyes on a raised mound give the spider almost no useful vision — it navigates and hunts by touch, using sensory hairs that pick up air currents and ground vibrations.

Defence

A cornered goliath birdeater has a graduated set of warnings:

1. Hissing — rubbing bristles on its legs together to produce a rasp audible from several metres.
2. Rearing — lifting the front legs and body to expose the fangs.
3. Hair-flicking — using the back legs to kick a cloud of tiny urticating hairs off its abdomen. Each hair is barbed, and they lodge in skin, eyes, and airways, causing hours of intense itching and burning. This is the spider’s main deterrent against mammals, and it is why it often has a bald patch on its abdomen.
4. Biting, only as a last resort. The bite hurts and bleeds because of the fang size, but the venom itself is mild.

Diet and hunting

Despite the name, birds are a tiny and incidental part of the diet. A goliath birdeater eats whatever it can overpower near its burrow: large beetles, crickets, cockroaches, earthworms, and small vertebrates including frogs, lizards, mice, and young snakes. It seizes prey, pumps in venom and digestive juices, and sucks out the liquefied tissue over several hours.

Reproduction and life cycle

A mature male leaves his burrow and wanders in search of a female, drumming on the ground at burrow entrances. Mating is risky — the male uses hooks on his front legs to hold the female’s fangs back and must retreat quickly, and is often eaten if he is slow. The female produces a silk egg sac containing 50 to 200 eggs and guards it in the burrow for six to eight weeks. Spiderlings disperse after their first moult.

People and the goliath birdeater

The species has not been formally assessed by the IUCN. It is locally common where suitable forest remains, but it is collected for the exotic pet trade and, in parts of its range, roasted and eaten as a traditional food. Its main long-term threat, like most rainforest animals, is deforestation.