Of the 900 or so known tarantula species, almost all are harmless (Isbister et al. 2003, Lucas et al. 1994). A bite by any large spider can be painful even if no venom is injected, since the fangs themselves are essentially big needles. Even if venom is injected, however, most tarantula bites result in little more than local pain and swelling. When there are medical problems, the cause is usually shock or an allergic reaction, rather than the action of the venom itself.
That said, not all tarantulas are equally venomous. The most common tarantulas sold in pet shops are all pretty benign: the Chilean rose hair, the Mexican redknee, and the pinktoe tarantulas have both mild venom and docile habits. They can be handled gently with almost no risk of being bitten.
Other, more exotic species kept by seasoned tarantula experts include the cobalt blue, the goliath birdeater, and the golden starburst tarantulas. These are beautiful and impressive captives — the goliath birdeater can attain a 12-inch leg span. The cobalt blue and golden starburst are stunningly colorful animals, the latter approximately matching the color of Donald Trump’s hair. These species are also more nervous and willing to bite, and their bites are generally more painful (e.g., Takaoka et al. 2001).
Avid tarantula enthusiasts don’t get most of their spiders from pet shops. Instead they buy tarantulas from other spider-keepers who breed their pets, or from companies that import spiders and other animals from around the world. With international trade, hundreds of species are available for hobbyists collect. Many of these are poorly known, most have not had their venom studied, and a few haven’t even been formally described by scientists.
Where venomous animals are concerned, gaps in scientific knowledge can have serious consequences. A few years ago a Swiss man was bitten by one of his many pet tarantulas — at first, the only symptoms were mild pain, hot flushes and sweating. He brought himself to the hospital 15 hours later, when he began to experience severe muscle cramps and stabbing chest pain. Doctors gave him medication (midazolam and lorazepam) that reduced the symptoms, but muscle cramps did not disappear completely until three weeks after the bite (Fuchs et al. 2014). The tarantula in this case was a regal ornamental tarantula, a magnificent tree-dwelling spider native to India.
There are at least 16 species of ornamental tarantulas, all from tropical forests in India and Sri Lanka. Most of them can be found in the exotic pet trade, and many have become popular with tarantula keepers looking for something a little more exciting. Exciting is certainly what they get: ornamental tarantulas are stunningly beautiful, as well as extremely fast and agile climbers. They are also quick to bite if cornered. Ornamental tarantula venom, while not deadly, is certainly underestimated.
To see if muscle cramps and chest pain were common symptoms of ornamental tarantula bites, Joan Fuchs and colleagues (2014) looked at 26 case reports, most of which were blog entries by seasoned tarantula keepers and breeders. Of the cases, 58% involved muscle cramps, along with other symptoms such as fever and heavy breathing. A few patients even lost consciousness for short periods. All bites were painful, but those that led to muscle cramps were severely so. This led the researchers to believe that, in cases where muscle cramps did not appear, the spider had simply injected much less venom.
It’s worth remembering that no tarantula bite has ever been fatal. It is a sorry fact, however, that by far the greatest source of knowledge on tarantula bites comes not from scientists, but from spider-keepers who take great pains (literally) to record their symptoms after every bite. This information is shared with other spider-keepers online at websites like Arachnoboards, so other hobbyists know what to expect from each species.
Such informal reports have been done for many species that have yet to be studied closely by scientists, and some that haven’t even been “discovered” (i.e., been given Latin names and formally described). The scientific axiom that “more work is needed” may be a cliché, but regarding tarantula bites and spider venom in general, it is certainly true.
Fuchs J., M. von Dechend, R. Mordasini, A. Ceschi, and W. Nentwig. 2014. A verified spider bite and a review of the literature confirm Indian ornamental tree spiders (Poecilotheria species) as underestimated theraphosids of medical importance. Toxicon 77: 73-77.
Isbister G.K., J.E. Seymour, M.R. Gray, and R.J. Raven. 2003. Bites by spiders of the family Theraphosidae in humans and canines. Toxicon 41(4): 519-524.
Lucas S.M., P.I. Da Silva Júnior, R. Bertani, and J.L. Cardoso. 1994. Mygalomorph spider bites: a report on 91 cases in the state of São Paulo, Brazil. Toxicon 32(10): 1211-1215.
Takaoka M., S. Nakajima, H. Sakae, T. Nakamura, Y. Tohma, S. Shiono, and H. Tabuse. 2001. Tarantulas bite: two case reports of finger bites from Haplopelma lividum. The Japanese Journal of Toxicology 14(3): 247-250.