Did you know that tarantula urticating hairs are actually really complicated?

Some may not agree with me, but I personally feel like as soon as I think I have a handle on tarantulas, I learn something that shows me I have way more to learn! Perhaps you can relate. I had been in the tarantula keeping hobby for years and thought I had quite a bit of research under my belt – until I learned over the last year that urticating hairs are more than itchy painful barbs that your tarantulas flick off at you when they’re feeling sassy!

What are urticating hairs, or urticating setae? In case you were not aware, these are the very itchy and irritating hairs that tarantulas carry on the backs of their abdomens. These are the hairs they kick off at predators or percieved threats. Most people usually just get these on their hands and arms, and get a very itchy rash that goes away after a while, but some poeple are highly allergic to these hairs and find it very painful. In the event that these hairs get into your nose or eyes, or anywhere near your face, you may have a very big problem on your hands!

Interesting enough, old world tarantulas do not have urticating setae – and this is why their venom is so much stronger than new world tarantulas. New world tarantulas have both venom (though less potent) and the urticating hairs, and will usually use the hairs as their go-to defense first before biting. Here’s something I didn’t know – not only will tarantulas protect themselves by flicking these hairs, they will also place these hairs on their molting mats and cocoons with fertilized eggs as an extra protective measure. Spiders are so smart! That being said, “it’s recommended to use some kind of gloves when you’re working inside the cage of a new world tarantula. Make no mistake, there is nothing like a resistance factor. The effect of the hairs on your body will get worse, year by year.”

Most (about 90%) of new world tarantulas possess the urticating setae, and there are actually several different types of setae depending on the tarantula. There are, as we know, 7 types of these urticating hairs, as summarized by Theraphosidae.be:

Type I

• 0,2-0,6mm.

• Embedded by a penetrating tip.

• Belongs to the subfamilies of the Aviculariinae and Theraphosinae, with exception of Grammostola spp.

• Vitalius spp., Nhandu carapoensis and Proshapalopus amazonicus are armed with only this type of urticating setae.

• Very effective against invertebrates, both actively and passively in webs and cocoons. Some larva are being perforated and killed by setae type I (example).

Type II

• 0,5-1,5mm.

• Embedded by a penetrating tip.

• Belongs to the subfamily of the Aviculariinae, more specific Avicularia spp., Pachistopelma spp. en Iridopelma spp.

• This type is not being bombarded. In order to make use of them, direct contact is necessary.

Type III

• 0,3-1,8mm.

• Embedded by a penetrating tip.

• Belongs to the subfamilies of Aviculariinae and Theraphosinae.

• Most efficiënt type against vertebrates and invertebrates.

• Very irritating for mammals.

Type IV

• 0,06-0,2mm.

• Embedded by a penetrating tip.

• Belongs to the subfamilies of the Aviculariinae and Theraphosinae, more specific Grammostola spp.

• Very irritating for mammals.

Type V

• Very short and light compared to other types of urticating setae.

• Embedded in hair follicle.

• Belongs to Ephebopus spp. (Marshall & Uetz/1990).

• Located on the femura of the pedipalpen.

Type VI

• Embedded in hair follicle.

• Belongs to Hemirrhagus spp. (Pérez-Miles/1998).

Type VII

• Differs from others by having a small distal oval patch of lanceolate reversed barbs near the penetrating tip and small main barbs that extend along the whole setae from the apex.

• Belongs to Kankuamo spp.Perafán, Galvis & Pérez-Miles, 2016

Here’s a great video by The Tarantula Collective about the tarantulas that have the most brutal urticating hairs!