Lasiodora

Physical description and identification

Lasiodora is a genus of very large terrestrial tarantulas in the family Theraphosidae, subfamily Theraphosinae, infraorder Mygalomorphae — the group whose fangs strike straight down. Carl Ludwig Koch described the genus in 1850, and more than thirty species are recognised, the great majority of them Brazilian. One of them, the salmon pink birdeater (Lasiodora parahybana), is one of the two or three largest spiders in the world by leg span.

Adults

• Size: the figure of 3–11 inches quoted for the genus is a leg span and not a body length. Body length in the largest species reaches about 9–10 cm; the leg span of a big L. parahybana female can approach 28 cm (11 in), and the animal may weigh well over 100 g. Males mature smaller, with longer legs and a much slimmer abdomen.
• Colour: most species are dark brown to black overall. Many carry paler bristle tips that give a frosted or salmon-pink wash across the legs and abdomen — the source of the name of L. parahybana — and L. difficilis develops distinctly pink-toned legs as it matures.
• Eyes: eight small eyes grouped on a low mound at the front of the carapace. Sight is poor; the spider works by vibration and by touch through the hairs on its legs.
• Distinctive features: sheer bulk, thick, densely haired legs, and a patch of urticating setae on the top of the abdomen. Adult males have swollen palpal bulbs and hooks on the front legs for restraining a female's fangs during mating.

Eggs and egg sac

Females are extremely fecund. A large L. parahybana can lay upwards of a thousand eggs, and clutches of close to two thousand have been recorded, wrapped in a heavy silk sac that the female turns, moves and defends for weeks. Other species in the genus produce smaller clutches.

Spiderlings

Spiderlings emerge unusually large — big enough to take substantial prey immediately — and are already miniature versions of the adults in shape, though far paler. They disperse on foot rather than ballooning and grow quickly through their first year, then slow down, taking several years and many molts to reach adult size.

The burrow and hunting

No Lasiodora builds a capture web. The common claim that they "do not make webs" nonetheless undersells the silk: it lines the burrow, mats the ground at the entrance so that footsteps register, forms the sheet a spider lies on to molt, and is spun into the sperm web by adult males. The genus lives in burrows, under logs and stones, and in cavities among tree roots on the forest floor, coming to the entrance after dark and ambushing whatever walks past. For how that compares with other hunting strategies, see our guide to what spiders eat.

Where Lasiodora tarantulas live

The centre of the genus is Brazil, which holds the overwhelming majority of described species, with a handful in neighbouring South American countries. The genus also reaches Central America: Lasiodora puriscal is a Costa Rican species, so describing the group as purely South American is not quite right.

The habitat is broader than "rainforest", a description often repeated and only partly true. L. parahybana comes from the Atlantic forest remnants of Paraíba in north-eastern Brazil — warm, seasonal forest rather than permanently soaked jungle — while other species occupy humid coastal forest, cerrado savanna and drier scrub. What they have in common is a forest or scrub floor with deep leaf litter, fallen wood and soil loose enough to excavate.

Because they are ground animals in a hot climate, the burrow does most of the work of keeping the spider alive: it buffers temperature, holds humidity through the dry season and hides an otherwise very conspicuous animal from birds and mammals.

Are Lasiodora tarantulas venomous?

Yes, like nearly all spiders, and no, not dangerously. The venom is adapted to invertebrate prey; there is no antivenom for any theraphosid because none is needed, and no human death has ever been attributed to a tarantula bite. Published series of theraphosid bites describe pain, puncture wounds, bleeding and local swelling that resolve within hours to a couple of days.

The defence that matters more is the hair. As New World theraphosines, Lasiodora species carry urticating setae on the upper abdomen — barbed bristles that the spider kicks off with its hind legs in a cloud toward a threat. L. parahybana is a notably enthusiastic flicker, and the setae cause itching, welts and a rash that can last a week or more; in the eye or the airway they cause genuine injury. Old World genera such as Cyriopagopus have no urticating setae at all and answer disturbance with a far more painful bite instead.

Can Lasiodora tarantulas bite?

They can, and in a spider this size the fangs alone are worth respecting — they can exceed a centimetre and go through skin like two large needles. But biting is not the first response. A disturbed Lasiodora retreats, and if cornered it raises the front of its body, rubs its hind legs across the abdomen and throws hairs. Only a spider that is pinned or grabbed is likely to bite.

The result is sharp mechanical pain, two deep puncture marks, bleeding and swelling that settle over a day or two. Clean the wound thoroughly with soap and water, apply a cold pack and keep it covered — the realistic complication from a large tarantula is a secondary bacterial infection of the punctures rather than any effect of the venom. Get medical advice if pain worsens, redness spreads, or there are signs of an allergic reaction.

Ecological importance and behavior of Lasiodora tarantulas

Lasiodora is a nocturnal ambush predator of the forest floor and a solitary animal outside mating. Despite the name birdeater, the diet is overwhelmingly invertebrate — crickets, roaches, beetles, grasshoppers, millipedes — with occasional small vertebrates such as frogs, lizards and nestling rodents for the largest females. Birds are an exceptional prey item, not a habit.

Natural predators: the specialists are pompilid spider wasps, which paralyse an adult tarantula and seal it with a single egg. Coatis, opossums, snakes, large lizards and birds take exposed spiders, particularly wandering males, and parasitic flies and nematodes attack egg sacs and adults. A spider of this size has fewer predators than a small one, but it is far from untouchable.

Prey-predator dynamics: a big theraphosid removes a substantial quantity of ground invertebrates over a lifetime, and the burrows themselves become shelter for frogs, lizards and other invertebrates once abandoned.

Seasonal behaviour: mature males leave their retreats and wander for weeks looking for females, usually after the onset of the rains, and it is these males that people find crossing tracks and entering buildings. Females keep molting and living — commonly fifteen to twenty years and sometimes longer — while males rarely survive much past a year after their final molt.

Relationship with humans: harmless in any medical sense but intimidating by size, which makes the genus a frequent casualty of fear. It is also one of the most commonly bred tarantulas in captivity precisely because of its fecundity, which reduces the pressure to collect wild animals.

Species in the genus and similar tarantulas

Quick facts

Did you know?

• The genus was erected in 1850 by Carl Ludwig Koch, the German arachnologist and entomologist — not by his son Ludwig Koch, who is often credited by mistake and who worked a generation later.
• Lasiodora parahybana was described in 1917 by the Brazilian zoologist Cândido Firmino de Mello-Leitão and takes its name from Paraíba, the state where it was found.
• "Birdeater" comes from an eighteenth-century engraving of a tarantula eating a hummingbird, not from anything these spiders normally do. Vertebrates are a rare bonus in a diet of insects.
• A single L. parahybana egg sac can hold more spiderlings than most spider species produce in a lifetime — well over a thousand.
• Hairs lost to flicking leave a bald patch on the abdomen that only grows back at the next molt, which is why an old, defensive tarantula often looks worn on top.

In summary, Lasiodora is the Brazilian heavyweight of the tarantula world: enormous, dark, ground-dwelling and hugely fecund. Its venom is unremarkable, its fangs are impressive, and the thing that actually reaches most people is the cloud of itching hairs it throws before it ever considers biting.