Something many new keepers get dismayed or worried about is their tarantula’s tendency to lose hairs on their abdomen, leading them to ask why their spider has developed a bald spot.
Tarantulas bald because they either lose urticating hairs or continually rub against something abrasive. Some New World tarantulas can develop a bald spot on their abdomen because this is where their patch of urticating hairs is located. They kick these hairs in an attempt to defend themselves whenever they are feeling cornered or provoked. The more often they kick the hairs away the more apparent the bald spot will become, and it won’t fill back in again until they molt.
What are the hairs on a tarantula called?
Tarantulas don’t have hair, they have setae. However, in this post, I’ll be referring to them as hairs because it’s far more common to come across people asking questions about “urticating hairs” versus “urticating setae.” The area where a tarantula typically becomes bald is where their patch of urticating hairs is located, which is correctly referred to as urticatious setae or urticating setae.
Can all tarantulas develop a bald abdomen?
Any tarantula can develop a tiny bald patch underneath their abdomen if the abdomen is constantly dragging because they were overfed to the point of being obese. However, not all tarantulas can develop a bald patch on the top of the abdomen.
Not all tarantulas have urticating hairs, and only the species that have abdominal urticating setae will have the ability to develop a bald abdomen due to the loss of urticating hairs (there are five different types of urticating hairs that can be found on the abdomen). Old World tarantulas do not have urticating hairs. With a few exceptions, almost all New World tarantulas have these defensive hairs.
This is what the paper, The Urticating Hairs of Theraphosid Spiders published by the American Museum of Natural History, says about urticating hairs being found outside of New World tarantulas (pg 4):
“Urticating hairs appear to be restricted to New World representatives of the theraphosid subfamilies Ischnocolinae, Grammostolinae, Theraphosinae, and Aviculariinae, but do not occur on every species. So far as we can determine there is nothing to suggest that urticating hairs are found outside the New World and certainly none was present on the extensive material we examined.”
Some examples of NW genera that lack urticating hairs include Psalmopoeus, Dolichothele, and Tapinauchenius. Notice how the aforementioned genera contain species that are known to be teleporters or to have a feisty temperament?
This is usually the tradeoff when a tarantula lacks the line of defense that urticating hairs provide. The genus Avicularia possesses urticating hairs, but they don’t flick them.
Why does a tarantula kick hairs?
Urticating hairs are intended to be a deterrent for predators. A tarantula will employ them when they feel threatened, which may translate into when they are being handled, if they are accidentally breathed on, manipulated with a paintbrush, being rehoused, or if they are startled during spot cleaning.
New World tarantulas also use their urticating hairs as protection against predators while they are molting. They will lay down a molting mat of thick webbing and kick a bunch of hairs onto it so that they are surrounded by a dense patch of them. This is one of the reasons why many keepers use gloves and a mask to perform cage maintenance for NW specimens.
Do urticating hairs contain venom?
The urticating hairs on a tarantula do not contain venom or any other chemical toxin to create the irritation. The hairs are barbed and highly irritating to mammalian mucous membranes and skin. There are different types of hair structures, and each one has a varying configuration and size of these barbs.
While there are multiple types of urticating hairs present across tarantulas, the irritation that they all cause is due to the mechanical damage that they create and the subsequent allergic reaction a person may experience.
People who are sensitive to them are reacting to the proteins found in the structure of the hairs, not to a chemical that is on the hairs. Some species, like those found in the genus Theraphosa, are known to produce particularly strong reactions.
Over time, it’s possible that you may become more sensitive to urticating hairs if you regularly interact with New World tarantulas. This is why I always recommend wearing protection (such as gloves, long sleeves, safety glasses, and a mask) during cage maintenance and any interactions.
Can you stop a New World tarantula from kicking hairs?
You cannot completely stop a tarantula from kicking urticating hairs. However, you can minimize the things that provoke them into kicking. For example, if your tarantula is primarily kicking hairs because you are attempting to handle them, then this is a good indication that you should stop doing that.
I personally try to keep interactions with my tarantulas to a minimum because I feel that it is best for the spider. This means that I wait to do any cage maintenance until they are in their burrow or under their hide.
I also make sure that I remove any live feeders after 24 hours because I have seen my tarantulas flick hairs at crickets that become too much of a nuisance. Usually, this is enough to keep most of them from developing bald abdomens.
Unfortunately, some specimens will still startle easily and begin kicking the moment the lid is disturbed. You can’t avoid this.
Is a bald spot harmful to a tarantula?
Kicking urticating hairs is a completely normal behavior for New World tarantulas. It is not harmful for them to have a bald spot, and even though it is unsightly, it doesn’t mean that anything is wrong with the spider.
However, if the bald spot is due to repeated friction because the tarantula is constantly rubbing on something, then you should take the time to double check that there’s nothing sharp or overly abrasive in the enclosure.
Will a tarantula always have a bald spot on top of their abdomen?
Although it may seem like your NW tarantula has a perpetual bald spot, they really don’t. Every time the tarantula molts, the new exoskeleton will have a complete patch of urticating hairs. How long it will take for the tarantula to make their abdomen bald again will vary between individuals.
Final Thoughts on Hair Flicking
The haggard appearance that some New World terrestrials take on because of their predisposition to flicking hairs is a deterrent for some keepers, leading them to prefer species that lack urticating hairs as a defense.
Some specimens are more prone to hair flicking than others, and will immediately begin kicking after they harden up from a molt. For example, my Aphonopelma chalcodes and my Grammostola pulchra almost never flick hairs, so their abdomens don’t end up looking scruffy and bald between molts.
In comparison, all of the Aphonopelma marxi that I have will readily flick hair if I start opening the enclosure. My Chromatopelma cyaneopubescens are prolific hair flickers – I rarely see them with a fully covered abdomen.
Don’t let hair flicking deter you from keeping popular New World species! Just know that it’s perfectly normal for them to not always look as pretty as they did right after a fresh molt, and make sure you keep yourself safe by minimizing your exposure to the hairs.