Are Tarantulas Dangerous? Venom, Bites and Itchy Hairs

Are tarantulas venomous?

Yes. Like almost all spiders, every tarantula has a pair of venom glands that open through its fangs. The venom is a mix of toxins that paralyzes insects, other invertebrates and the occasional small vertebrate, and it starts breaking down the prey’s tissues. It evolved to subdue prey, not to fight off large mammals, and for most species its effect on people is weak.

Venomous is not the same as dangerous. A spider’s danger depends on how potent its venom is for humans, how much it injects and how big its fangs are. Tarantulas have big fangs, so their bites hurt, but their venom rarely causes more than local symptoms. The wider question is explored in are all spiders venomous?

What happens if a tarantula bites you?

Most tarantula bites cause sharp pain, redness and swelling around two small puncture wounds, much like a bee or wasp sting. The pain often fades within hours. Some bites are “dry”: the spider bites in defense but injects little or no venom.

A few people react more strongly. As with bee stings, some may have an allergic reaction to proteins in the venom, which can be serious. The punctures can also become infected like any other wound. Anyone who has trouble breathing, widespread swelling or other severe symptoms after a bite should seek emergency medical help immediately (911 in the US, 112 in the EU, 999 in the UK).

Urticating hairs: the itchy defense

Most tarantulas from the Americas, including the Goliath birdeater and the Mexican red-knee tarantula, carry a special defense on their abdomen: urticating hairs. These are tiny bristles with barbs or hooks that break off easily. When threatened, the spider turns away and kicks its back legs against its abdomen, sending a cloud of hairs toward the attacker. Some tree-dwelling species press the hairs directly against an enemy instead.

The hairs work their way into skin and mucous membranes. On skin, they cause itching, redness and rashes that can last for days or even weeks. In the nose and throat, they cause irritation and sneezing. The most serious problems occur when hairs get into the eyes, where they can embed in the surface and inner tissues; doctors have reported cases of inflammation lasting months. The hairs are especially effective against small mammals, such as rodents, that sniff around burrows.

Urticating hairs are found only in tarantulas of the Americas. Several different types are known, and their strength varies between species; the Goliath birdeater’s hairs are considered among the most irritating. A tarantula cannot regrow hairs it has used until its next molt, so a bald patch on the abdomen is a sign it has been defending itself.

Old World tarantulas: stronger venom

Tarantulas from Africa, Asia and Australia have no urticating hairs. Instead, they tend to be faster, more defensive and quicker to bite, and some have more potent venom.

The best-documented examples are the Indian ornamental tarantulas (genus Poecilotheria) of India and Sri Lanka. Case reports describe bites that caused severe muscle cramps beginning hours after the bite and lasting for several days. Bites from African baboon spiders, such as the king baboon spider, are also reported to be very painful. These spiders can make people quite ill, but no deaths have been documented.

Venom effects also differ between victims. An Australian study of bites by local tarantulas, published in 2003, found that people usually had only minor symptoms, while dogs bitten by the same kinds of spiders became seriously ill, and some died.

Warning signs: how tarantulas defend themselves

Tarantulas avoid conflict whenever they can. Most are nocturnal and spend the day in burrows, under logs or in silk retreats. When disturbed, they usually escalate their defenses step by step:

1. Freezing or running back into the burrow.
2. Rearing up into a threat posture, with the front legs raised and fangs displayed.
3. Slapping down with the front legs.
4. Flicking urticating hairs (American species).
5. Hissing by rubbing bristles together, in species such as the Goliath birdeater and the king baboon spider.
6. Biting, as a last resort.

Most bites happen when people pick up or provoke a spider. Admiring a tarantula without touching it is the simplest way to stay safe.

Spiders that really are dangerous

Some of the world’s most venomous spiders are confused with tarantulas. Australian funnel-web spiders belong to the same broad group of heavy-bodied spiders, the mygalomorphs, and their venom can be life-threatening, although no one has died from a funnel-web bite since an antivenom was introduced in 1981. Brazilian wandering spiders of Central and South America, large and hairy but not tarantulas at all, also have medically significant venom. Rumors of deadly “banana tarantulas” usually refer to these wandering spiders.

Even the name “tarantula” began with a misunderstanding. It originally referred to a wolf spider of southern Italy, Lycosa tarantula, whose bite was once blamed for “tarantism”, a condition supposedly cured by frenzied dancing. In fact, its bite is mild. For spiders whose bites genuinely need medical care, see our list of the most venomous spiders and our guide to venomous spiders in the US.