The great thing about this question is that I am often asked this while I have a tarantula crawling on my hand. Now, I like some excitement in my life, but putting myself at risk is not my idea of fun. If tarantulas were dangerous, I would definitely not be impressing anyone by holding one.
Are Tarantulas Poisonous to Humans and Other Animals?
First of all, if you were bitten by a tarantula (unprovoked), then congratulations – you are now a member in a very elite club. If you were bitten by a tarantula, there is a good chance that very little venom (if any) was injected. As far as being “poisonous,” all spiders, including tarantulas, have venom.
The primary defense of ALL the tarantulas I have observed is running and hiding. Second to that, some tarantulas from the Americas (New World) defend themselves by flicking tiny, irritating bristles (urticating hairs) more often than they will defend themselves via biting.
Prescription-strength cortisone or a shower with alternating hot and cold water can soothe the itching caused by urticating hairs.
The uritcating hairs can cause one to itch for a few hours or, in a sensitive individual such as myself, cause a rash and irritation for a few days. Definitely DO NOT rub your eyes after handling a New World tarantula, as the urticating hairs can damage the cornea
(Note: do not pick your nose after handling a New World tarantula. You shouldn’t pick your nose anyway).
Most “Old World” tarantulas (tarantulas from Asia and Africa) will rear up on their hind legs in an attempt to frighten a harasser if running and hiding don’t work (keep in mind that there’s only so many places to run and hide when you live in an aquarium).
Most Old World species are usually quick to bite if warning doesn’t ward off a potential threat like your hand. Overall, I have NEVER seen a tarantula that was truly “aggressive” in the sense that it would attack unprovoked. Those I deem “aggressive” on this site are ones that are just more prone to defending themselves.
Almost all spiders possess venom, but no known tarantulas have venom of significant consequence to healthy humans. The general reaction to their bites is some physical damage from the fangs piercing the skin (which is no big deal from a small spider, but a bite from a Theraphosa blondi with half-inch fangs may be something like poking a sharpened fork in your hand) and perhaps aching or cramping, some swelling, and local redness.
However, it may be possible that an individual could be more sensitive to tarantula venom than others given the situation and the individual’s health. Also, some varieties such as Pterinochilus spp. or those of the subfamilies Stromatopelminae and Selenocosmiinae have venom that may cause adverse swelling and irritation, much like a wasp’s sting, or even more severe consequences like vomiting.
The Ornamental spiders of India and Sri Lanka (Poecilotheria) are suspected of having venom that may cause detrimental reactions ranging from respiratory discomfort to muscle cramps.
NOTE: I used the words “suspected” and “rumored”; very little is known and even less is scientifically documented about tarantula bites. There is no telling how much venom was injected in the scant medical literature available, if any was injected at all (it is up to the spider whether or not to use its venom, and it may control how much it uses).
Furthermore, web forum anecdotes about spider bites are just that- anecdotal. Studies with careful controls will have to be done to make an acceptable determination regarding certain species, but it can be safely said that most tarantulas can’t hurt a healthy, semi-intelligent adult any more than a wasp or a cat could.
Consider this: With as many tarantulas as there are in our homes and in the wild, I have yet to hear a reliable report of a single human death caused by one, and reports of more than minor reactions to bites are very few and far between. . .in fact, just getting bitten is not a common occurrence at all.
Most tarantulas will warn before biting in defense by rearing up on their hind legs and baring their fangs, but this may not be true of some arboreals. Venom is not always injected when biting (it’s up to the spider when and how much venom they use) and I’ve observed several species give slapping “warnings” with their forelegs instead of immediately gouging their fangs in for all they’re worth.
Based on my observations, two things are apparent: (1) Tarantulas would prefer to avoid negative confrontations. (2) Tarantulas can differentiate a hand from prey.
The best advice for avoiding a “spat” with a tarantula is use common sense: If it seems like it wants to be left alone, leave it alone. If it’s a known defensive/high strung species, don’t get experimental and taunt it like a jackass. If it’s normally docile, expect it to have its bad days just like you do (yes, they do have “moods”, or at least behavioral reactions to a wide range of stimuli).