Urticating Setae: A Look at the Evidence

Written by Dr. M. Dalal,. Physician, biologist, and founder of Tarantula Cribs.

Every New World keeper gets hit eventually. Most of the advice that circulates about what to do afterward is inherited rather than sourced, so I went and pulled the papers. Some of it holds up. One widely repeated piece of it does not.

They aren't hairs

Only mammals grow hair. What tarantulas carry are setae, modified bristles sitting on the dorsal and lateral opisthosoma. Ephebopus is the odd one out, carrying them on the pedipalpal femora instead.

They're also strictly a New World trait. Cooke, Roth and Miller established that in their 1972 monograph and it still holds up: no Old World theraphosid has them. Bertani and Guadanucci later put the number at roughly 540 of about 600 described Neotropical species. Psalmopoeus, Tapinauchenius and the ischnocolines are the New World exceptions.

Seven morphological types are recognized now. Kaderka and colleagues revised the typology in 2019 after examining 144 taxa, reclassifying a number of setae previously filed under Type III as developmental subtypes of Type I. Type VII was added in 2016 from the Colombian genus Kankuamo, and it's an interesting one because it appears to transfer by direct contact rather than being kicked.

For a keeper, the type that matters is III. Those setae are longer, thicker, and penetrate deeper than the rest, and they're the ones behind the more serious outcomes in the medical literature. They're also what your Brachypelma, Lasiodora, Nhandu, Acanthoscurria and Theraphosa are throwing at you. Type I setae are smaller and aerosolize more readily, which is why they turn up in respiratory complaints instead of dermal ones.

The reaction is mechanical

This governs everything that follows, so it's worth being precise about.

An urticating seta is a barbed shaft. The barbs are reversed, angled back along the length, so the seta advances easily and resists coming out. There's no venom gland and nothing injected. That makes it a different situation from caterpillar setae, which do deliver an urticating toxin through a hollow shaft.

What you're dealing with is a foreign body reaction to a barbed object lodged in tissue. Three consequences follow.

Antihistamines don't do much. The reaction isn't primarily histamine driven. If you've developed a true hypersensitivity to the protein component over years of keeping, they may take the edge off, but they aren't touching the cause.

Anything that pushes is worse than anything that pulls. Rubbing, scratching and scrubbing drive barbed shafts deeper. That isn't folklore, it follows from the geometry.

And time isn't neutral. Setae migrate. In the eye, that migration is the whole clinical problem.

Skin

The usual presentation is an itchy papular rash, sometimes with visible dark puncta, showing up within minutes to hours and hanging around for days to weeks. In one documented case from Taiwan, a keeper came in with tingling and numbness in the fingertips after contact with Grammostola rosea. A KOH skin scraping recovered the setal fragments directly. Symptoms cleared over about a week on a topical steroid.

The reasonable approach:

1. Stop touching it. No rubbing, no scratching, no aggressive washing.
2. Get the loose material off. Change clothes and wash them separately in hot water.
3. Topical corticosteroid. This is the mainstay in the published case reports. OTC hydrocortisone for a mild exposure, prescription strength if the reaction is significant.
4. Cool compresses for symptomatic relief.
5. Expect days rather than hours. Retained fragments work their way out over one to two weeks.

About the tape

Every guide in the hobby recommends duct tape. The evidence behind it is a lot thinner than the confidence with which it gets repeated.

There is no controlled study of setal removal from human skin. None. The closest comparable data comes from Martinez and colleagues in 1987, who ran a head to head comparison of removal methods for cactus glochids. Glochids are barbed, hair fine, and mechanically similar. What worked best was tweezers for the visible clumps, followed by a thin layer of ordinary white household glue covered with gauze, left to dry and then peeled off.

Adhesive tape did badly. In that study it produced more retained material and more inflammation at three days than doing nothing at all.

The honest caveat is that glochids aren't setae and animal skin isn't human skin, so none of this transfers cleanly. But it's the best comparative data anyone has, and it points the opposite way from what the hobby believes. If you're going to try mechanical removal, glue and gauze has better support behind it. If you're going to use tape anyway, press once and lift in a single motion instead of working the area over and over.

The eyes are the part that actually matters

Here the literature is not ambiguous, and this is where keepers consistently underestimate the risk.

Setae in the eye produce ophthalmia nodosa, a granulomatous foreign body reaction. The setae don't stay where they land. They migrate inward, and they keep going.

The published course is worth sitting with:

Hered and colleagues in 1988 described a keeper with setae in the eyelids, conjunctiva, corneal epithelium and stroma. Six months later, peripheral chorioretinal lesions appeared.

A nine year old presented at Moorfields with a red eye that everyone initially blamed on a playground scuffle. Slit lamp examination found setae at every level of the cornea, anterior uveitis, vitreous lesions and full thickness retinal infiltrates. The tarantula only came out after repeated questioning.

A 29 year old developed chronic panuveitis that failed 18 months of intensive topical steroid and eventually required pars plana vitrectomy.

Another case needed low dose topical dexamethasone for nine months to keep the inflammation quiet.

Reported outcomes run from simple conjunctivitis through keratitis, iritis, keratouveitis, and panuveitis with chorioretinitis. A 2003 review found only 14 cases in the literature at that point. A 2021 review in the American Journal of Tropical Medicine and Hygiene revisited the question as exotic keeping expanded.

If it happens to you:

1. Irrigate immediately with saline or clean water.
2. Don't rub. Nothing else you do matters as much as this.
3. See an ophthalmologist. Not urgent care, not a walk in clinic. Setae are effectively invisible without slit lamp biomicroscopy, and several published cases were missed on first examination.
4. Tell them you keep tarantulas, and lead with it. In more than one case report the diagnosis was delayed purely because nobody asked and the patient didn't think to say.
5. Go back if symptoms return. Delayed posterior segment involvement is documented months out. A quiet eye at two weeks doesn't close the file.

Breathing them in

Less well characterized. Type I and Type IV setae are small enough to go airborne, and keepers report rhinitis, wheezing and cough, mostly during substrate changes and enclosure cleaning. The formal literature is thin here, largely self report plus inference from what these setae do to wild predators.

There's a sensitization pattern worth paying attention to, though. Keepers frequently report that reactions get worse over years rather than settling down. That's consistent with an allergic component developing on top of the mechanical one, but it hasn't been rigorously studied. If your reactions are escalating, take it as a signal rather than an annoyance.

Prevention is the only part that works well

None of the treatments above are particularly effective. All of the evidence points the same direction, which is that the intervention worth investing in is not getting exposed.

Wear eye protection for any rehousing, substrate change or enclosure cleaning. Safety glasses are the single highest yield habit in this hobby and the one most keepers skip.

Keep your face away from an open enclosure. Most of the published ocular cases involve either handling or close range observation.

Treat moults and webbing as contaminated. Setae get incorporated into egg sacs and moult mats and stay irritating long after they're shed.

Work at arm's length with long tools, and work slowly. Fast movement stirs settled setae back into the air.

Wash your hands before touching your face. Hand to eye transfer is a documented route.

Enclosure design carries some of this load too. Front opening access means reaching in horizontally instead of leaning over an open top with your face above the animal. A lid that actually seals keeps settled setae contained between maintenance sessions. Enough floor space means you aren't working directly over the spider just to reach the water dish.

What this evidence is and isn't

There's no randomized trial behind anything in this article. The human literature on urticating setae is case reports, small series, and morphological work, plus extrapolation from mechanically similar injuries like glochids and caterpillar setae.

That's worth saying out loud instead of papering over. It means the ocular guidance is on solid ground, because the case literature is consistent and the outcomes were serious enough to get documented carefully. It also means the skin removal guidance is genuinely uncertain, and anyone telling you with total confidence which tape brand to buy is repeating hobby lore, not citing anything.

General information for keepers, not medical advice, and no substitute for being examined by someone who can actually look at you. For anything involving the eye, see an ophthalmologist.

References

1. Cooke JAL, Roth VD, Miller FH. The urticating hairs of theraphosid spiders. American Museum Novitates 1972;2498:1-43.
2. Bertani R, Guadanucci JPL. Morphology, evolution and usage of urticating setae by tarantulas (Araneae: Theraphosidae). Zoologia 2013;30(4):403-418.
3. Kaderka R, Bulantova J, Heneberg P, Rezac M. Urticating setae of tarantulas (Araneae: Theraphosidae): morphology, revision of typology and terminology and implications for taxonomy. PLoS ONE 2019;14(11):e0224384.
4. Perafan C, Galvis W, Gutierrez M, Perez-Miles F. Kankuamo, a new theraphosid genus from Colombia, with a new type of urticating setae and divergent male genitalia. ZooKeys 2016;601:89-109.
5. Hered RW, Spaulding AG, Sanitato JJ, Wander AH. Ophthalmia nodosa caused by tarantula hairs. Ophthalmology 1988;95(2):166-169.
6. Sheth HG, Pacheco P, Sallam A, Lightman S. Pole to pole intraocular transit of tarantula hairs, an intriguing cause of red eye. Case Reports in Medicine 2009;2009:159097.
7. Blaikie AJ, Ellis J, Sanders R, MacEwen CJ. Eye disease associated with handling pet tarantulas: three case reports. BMJ 1997;314(7093):1524-1525.
8. Chang PC, Soong HK, Barnett JM. Corneal penetration by tarantula hairs. British Journal of Ophthalmology 1991;75(4):253-254.
9. Spraul CW, Wagner P, Lang GE, Lang GK. Ophthalmia nodosa caused by the hairs of the bird spider, case report and review of the literature. Klinische Monatsblatter fur Augenheilkunde 2003;220(1-2):20-23.
10. Jalink MB, Wisse RPL. On the dangers of tropical spiders as a pet: a review of ocular symptoms caused by tarantula hairs. American Journal of Tropical Medicine and Hygiene 2021;105(6):1795-1797.
11. Hsu CK, Hsu MML, West RC, Chu YI. Skin injury caused by urticating hair of tarantula. Dermatologica Sinica 2007;25(3):232-235.
12. Martinez TT, Jerome M, Barry RC, Jaeger R, Xander JG. Removal of cactus spines from the skin: a comparative evaluation of several methods. American Journal of Diseases of Children 1987;141(12):1291-1292.