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Urticating hairs or setae are specialized barbed bristles found on approximately 90% of New World tarantula species native to North, Central, and South America. These hairs evolved as a sophisticated defense mechanism against potential predators and threats. When threatened, tarantulas will rapidly rub their hind legs against their abdomen, creating a cloud of these microscopic bristles that become airborne and can embed themselves in an attacker's skin, eyes, or respiratory passages. The term "urticating" derives from the Latin word "urtica" meaning nettle, reflecting the irritating sensation these hairs produce upon contact.
Research has identified seven distinct types of urticating hairs (designated as Types I through VII), each varying in size, shape, and barb distribution, with different types targeting specific predators. Type I hairs measure between 0.2-0.6 mm, Type II range from 0.5-1.5 mm, Type III span 0.3-1.2 mm, and Type IV are the smallest at 0.06-0.2 mm. These microscopic dimensions enable the hairs to penetrate deeply into skin and tissue, making them particularly effective defensive weapons. Type V urticating hairs represent a significant departure from Types I-IV in both location and structure. While precise size measurements are not definitively stated in the scientific literature, several important characteristics are documented. Type V hairs are unique to the genus Ephebopus and, unlike most urticating hairs that are located on the abdomen, these are found on the pedipalps (the appendages near the spider's mouth). They are described as this "much shorter and lighter in contrast with other types of urticating hair". Scanning electron microscopy has revealed that these hairs consist of "short, stout, barbed shafts in a densely packed, uniform array". The hair field for Type V is described as orange-gold in color, contrasting with surrounding darker hairs. They are easily thrown by the spider into the air during defensive displays.
Type VI urticating hairs are among the least documented of all urticating hair types. These hairs are found exclusively in the genus Hemirrhagus. Like Type V, they are embedded in the hair follicle rather than loosely attached for kicking defense. Unfortunately, from what I can find, the scientific literature accessible through these search results does not provide specific size measurements for Type VI urticating hairs. The rarity of the Hemirrhagus genus in collections and its limited study will account for the scarcity of detailed measurements, and general lack of information.
Type VII represents the most recently discovered urticating hair type, first described in scientific literature in 2016. This type is exclusive to the Colombian Kankuamo tarantula. Their most distinctive feature is their reversed barbs, which provide enhanced irritation capability. As with Type VI, specific size measurements for Type VII urticating hairs are not provided in any available scientific literature that I can find. This is likely due to their relatively recent discovery and the limited number of studies conducted on this specific tarantula species.
The development of these specialized hairs represents an evolutionary adaptation that provides New World tarantulas with an additional defensive capability beyond their venomous bite. Interestingly, tarantulas employ urticating hairs not only as an active defense against immediate threats but also as a form of territorial marking. These bristles can be found around burrow entrances, in webbing, and even incorporated into egg sacs to protect offspring from potential predators. This passive defense strategy demonstrates the remarkable versatility of urticating hairs in tarantula survival strategies. Among the numerous tarantula species possessing urticating hairs, certain genera and species consistently rank as producing the most severe reactions in humans. Based on multiple sources and extensive keeper experiences, a clear hierarchy emerges regarding which tarantulas possess the most problematic urticating hairs.
The Theraphosa genus unanimously occupies the top position across virtually all rankings of urticating hair severity. This genus includes the Goliath birdeaters—Theraphosa blondi, Theraphosa stirmi, and Theraphosa apophysis—which represent the largest tarantula species in the world. Their urticating hairs are particularly problematic due to a combination of factors: they possess Type III hairs exclusively (unusual among New World tarantulas), their large size means they have more hairs to deploy, and these hairs appear to cause particularly intense reactions. Exposure to Theraphosa urticating hairs frequently results in painful burning sensations, severe itching, and visible skin inflammation that can persist for weeks. One tarantula keeper described an incident where merely handling a Theraphosa stirmi molt caused dramatic skin inflammation, demonstrating that even indirect contact with these hairs can produce significant reactions.
Following the Theraphosa genus, the Nhandu species—particularly Nhandu coloratovillosus—rank consistently high for urticating hair severity. One keeper reported that cleaning an enclosure housing this species resulted in burning sensations lasting over 20 hours, with itching persisting for days afterward. Another keeper described how even working near Nhandu tripepii caused immediate burning sensations in the nose and throat, comparing the experience to "mild pepper spray"—a testament to how these hairs can affect respiratory passages even without direct contact.
The Brazilian giant white knee tarantula (Acanthoscurria geniculata) represents another species notorious for its particularly irritating urticating hairs. Keepers report that even spiderlings of this species possess hairs capable of causing weeks of itching, especially when lodged in the sensitive webbing between fingers. This species appears especially prolific in deploying its urticating hairs, often kicking them in response to minor disturbances such as routine maintenance.
Other species consistently mentioned for their problematic urticating hairs include the Lasiodora parahybana, Brachypelma hamorii & Brachypelma boehmei. The Chromatopelma cyaneopubescens deserves special mention not necessarily for the intrinsic irritation of its hairs but for its tendency to incorporate these hairs into its extensive webbing, creating hazards for unwary keepers during enclosure maintenance.While gbb spread hair in their web, Avicularia are known for rubbing their abdomen to release hairs rather then kicking them, they will do this to their web and keepers hands when handling which is often mistaken for "hugs", there is also disputing info on the severity their hairs.
The symptoms experienced following exposure to urticating hairs vary considerably between individuals and species, ranging from mild irritation to severe systemic reactions. Understanding this spectrum of responses provides valuable context for assessing the relative severity of different tarantula species' urticating hairs.
Initial contact with urticating hairs typically produces localized itching and redness, often described as similar to mosquito bites or fiberglass exposure. For species with more severe urticating hairs, particularly those in the Theraphosa genus, this initial itching rapidly progresses to an intense burning sensation. One keeper described the experience as "unbelievably itchy" with a feeling like "sharp itch that sometimes hurts underneath the skin, like you have something stuck under there but you can't get it out". This description effectively captures the mechanical nature of the irritation, as the microscopic barbed hairs physically embed themselves in the skin.
As symptoms progress, many individuals develop visible manifestations including welts, rashes, and in severe cases, small blisters. The skin between fingers proves particularly vulnerable to these effects, likely due to the thinner skin and difficulty in removing embedded hairs from these areas. Symptom duration varies dramatically, with mild exposures resolving in hours while more severe cases can persist for weeks. Several keepers report that symptoms can temporarily subside only to flare up again upon exposure to heat or when the affected area is scratched, suggesting the hairs remain embedded and active for extended periods.
Most concerning are the effects when urticating hairs contact sensitive tissues like the eyes, nasal passages, or lungs. Exposure to the eyes can cause significant pain, inflammation, and in severe cases, potential permanent damage including blindness. Respiratory exposure presents similarly serious risks, with keepers reporting immediate burning sensations in the throat and difficulty breathing following inhalation of airborne hairs. These risks highlight why many experienced keepers recommend protective equipment when working with species known for problematic urticating hairs.
An important factor affecting symptom severity appears to be repeated exposure. Unlike developing immunity, many keepers report that reactions to urticating hairs worsen with each subsequent exposure. As one source notes, "The effect of the hairs on your body will get worse, year by year". This progressive sensitization adds another dimension to understanding which species present the greatest long-term concerns regarding urticating hair severity.
Several factors beyond the specific tarantula species influence the likelihood and severity of urticating hair exposure. Understanding these risk factors enables tarantula keepers to develop effective protective strategies for minimizing exposure risks. Enclosure maintenance represents perhaps the highest-risk activity for urticating hair exposure. During substrate changes or enclosure cleaning, previously kicked hairs that have settled into the substrate can become airborne again, creating invisible clouds of irritating bristles. Species that kick hairs frequently as a defensive strategy, such as Lasiodora parahybana and Acanthoscurria geniculata, present particular risks during maintenance activities as their enclosures often contain substantial amounts of shed urticating hairs.
The webbing created by many tarantula species presents another significant risk factor. Species like Chromatopelma cyaneopubescens and the Avicularia group of Tarantulas incorporate urticating hairs into their extensive webbing. This incorporation of urticating hairs into webbing represents a passive defense strategy but creates significant exposure risks during routine care activities.
Tarantula size correlates positively with urticating hair severity, as noted by multiple sources. Larger species like those in the Theraphosa, Lasiodora, and Acanthoscurria genera not only possess intrinsically more irritating hair types but also have larger abdomens with more hairs to deploy. This size factor partly explains why the largest tarantula species consistently rank highest for urticating hair severity.
Keepers have developed numerous protective strategies to mitigate exposure risks. The most commonly recommended approach involves wearing personal protective equipment during high-risk activities. Safety glasses provide essential protection against eye exposure, while masks prevent respiratory exposure, and gloves protect the hands and wrists. Keep duct tape close by, this can aid in removing hairs, steroid cremes also work for affected areas. One keeper who experienced eye exposure to Theraphosa stirmi hairs reported needing three separate doctor visits to have the hair removed.
Handling techniques also play a crucial role in minimizing exposure risks. Using tools rather than hands whenever possible, working slowly to avoid startling the tarantula, and maintaining appropriate distance from species known for kicking hairs can significantly reduce exposure incidents. Some keepers recommend using springtails in enclosures to help process organic matter, reducing the frequency of needed maintenance and thus lowering exposure opportunities.
The examination of tarantulas with the most severe urticating hairs reveals a clear hierarchy dominated by the Theraphosa genus, followed closely by species in the Nhandu, Acanthoscurria, Lasiodora, Pamphobeteus, Xenesthis & Brachypelma genera. These findings have significant implications for both experienced tarantula enthusiasts and newcomers to the hobby.
For individuals considering which tarantula species to keep, awareness of urticating hair severity should factor prominently into decision-making. While species like Theraphosa stirmi might appeal due to their impressive size and feeding response, their exceptionally irritating urticating hairs present ongoing management challenges that should not be underestimated. Conversely, some New World species like Grammostola rosea possess relatively mild urticating hairs, potentially making them more suitable for keepers concerned about urticating hair reactions.
The progressive sensitization that many keepers experience with repeated urticating hair exposure warrants particular attention. Unlike many allergens where exposure can sometimes lead to desensitization, urticating hair reactions typically worsen over time. This pattern suggests that even keepers who initially experience minimal reactions should implement protective practices to prevent developing more severe reactions through cumulative exposure. It must also be mentioned that, the individual (keeper) may experience different reactions to different species. Like mentioned, the Grammostola Rosea has mild setae, although you could experience sever symptoms.
For the tarantula keeping community as a whole, continued documentation and sharing of experiences regarding urticating hair severity provides valuable practical knowledge. The variation in individual responses means that collective experiences offer the most comprehensive picture of which species present the greatest concerns. Through careful species selection, appropriate protective measures, and respect for these remarkable defensive adaptations, tarantula enthusiasts can minimize the risks associated with even the most severe urticating hairs while continuing to appreciate these fascinating arachnids.
All Scientific information came from:
PubMed/PubMed Central
PLOS ONE
American museum of national history digital library and
SciELO.
The keeper reports are from here and TarantulaForum.
Research has identified seven distinct types of urticating hairs (designated as Types I through VII), each varying in size, shape, and barb distribution, with different types targeting specific predators. Type I hairs measure between 0.2-0.6 mm, Type II range from 0.5-1.5 mm, Type III span 0.3-1.2 mm, and Type IV are the smallest at 0.06-0.2 mm. These microscopic dimensions enable the hairs to penetrate deeply into skin and tissue, making them particularly effective defensive weapons. Type V urticating hairs represent a significant departure from Types I-IV in both location and structure. While precise size measurements are not definitively stated in the scientific literature, several important characteristics are documented. Type V hairs are unique to the genus Ephebopus and, unlike most urticating hairs that are located on the abdomen, these are found on the pedipalps (the appendages near the spider's mouth). They are described as this "much shorter and lighter in contrast with other types of urticating hair". Scanning electron microscopy has revealed that these hairs consist of "short, stout, barbed shafts in a densely packed, uniform array". The hair field for Type V is described as orange-gold in color, contrasting with surrounding darker hairs. They are easily thrown by the spider into the air during defensive displays.
Type VI urticating hairs are among the least documented of all urticating hair types. These hairs are found exclusively in the genus Hemirrhagus. Like Type V, they are embedded in the hair follicle rather than loosely attached for kicking defense. Unfortunately, from what I can find, the scientific literature accessible through these search results does not provide specific size measurements for Type VI urticating hairs. The rarity of the Hemirrhagus genus in collections and its limited study will account for the scarcity of detailed measurements, and general lack of information.
Type VII represents the most recently discovered urticating hair type, first described in scientific literature in 2016. This type is exclusive to the Colombian Kankuamo tarantula. Their most distinctive feature is their reversed barbs, which provide enhanced irritation capability. As with Type VI, specific size measurements for Type VII urticating hairs are not provided in any available scientific literature that I can find. This is likely due to their relatively recent discovery and the limited number of studies conducted on this specific tarantula species.
The development of these specialized hairs represents an evolutionary adaptation that provides New World tarantulas with an additional defensive capability beyond their venomous bite. Interestingly, tarantulas employ urticating hairs not only as an active defense against immediate threats but also as a form of territorial marking. These bristles can be found around burrow entrances, in webbing, and even incorporated into egg sacs to protect offspring from potential predators. This passive defense strategy demonstrates the remarkable versatility of urticating hairs in tarantula survival strategies. Among the numerous tarantula species possessing urticating hairs, certain genera and species consistently rank as producing the most severe reactions in humans. Based on multiple sources and extensive keeper experiences, a clear hierarchy emerges regarding which tarantulas possess the most problematic urticating hairs.
The Theraphosa genus unanimously occupies the top position across virtually all rankings of urticating hair severity. This genus includes the Goliath birdeaters—Theraphosa blondi, Theraphosa stirmi, and Theraphosa apophysis—which represent the largest tarantula species in the world. Their urticating hairs are particularly problematic due to a combination of factors: they possess Type III hairs exclusively (unusual among New World tarantulas), their large size means they have more hairs to deploy, and these hairs appear to cause particularly intense reactions. Exposure to Theraphosa urticating hairs frequently results in painful burning sensations, severe itching, and visible skin inflammation that can persist for weeks. One tarantula keeper described an incident where merely handling a Theraphosa stirmi molt caused dramatic skin inflammation, demonstrating that even indirect contact with these hairs can produce significant reactions.
Following the Theraphosa genus, the Nhandu species—particularly Nhandu coloratovillosus—rank consistently high for urticating hair severity. One keeper reported that cleaning an enclosure housing this species resulted in burning sensations lasting over 20 hours, with itching persisting for days afterward. Another keeper described how even working near Nhandu tripepii caused immediate burning sensations in the nose and throat, comparing the experience to "mild pepper spray"—a testament to how these hairs can affect respiratory passages even without direct contact.
The Brazilian giant white knee tarantula (Acanthoscurria geniculata) represents another species notorious for its particularly irritating urticating hairs. Keepers report that even spiderlings of this species possess hairs capable of causing weeks of itching, especially when lodged in the sensitive webbing between fingers. This species appears especially prolific in deploying its urticating hairs, often kicking them in response to minor disturbances such as routine maintenance.
Other species consistently mentioned for their problematic urticating hairs include the Lasiodora parahybana, Brachypelma hamorii & Brachypelma boehmei. The Chromatopelma cyaneopubescens deserves special mention not necessarily for the intrinsic irritation of its hairs but for its tendency to incorporate these hairs into its extensive webbing, creating hazards for unwary keepers during enclosure maintenance.While gbb spread hair in their web, Avicularia are known for rubbing their abdomen to release hairs rather then kicking them, they will do this to their web and keepers hands when handling which is often mistaken for "hugs", there is also disputing info on the severity their hairs.
The symptoms experienced following exposure to urticating hairs vary considerably between individuals and species, ranging from mild irritation to severe systemic reactions. Understanding this spectrum of responses provides valuable context for assessing the relative severity of different tarantula species' urticating hairs.
Initial contact with urticating hairs typically produces localized itching and redness, often described as similar to mosquito bites or fiberglass exposure. For species with more severe urticating hairs, particularly those in the Theraphosa genus, this initial itching rapidly progresses to an intense burning sensation. One keeper described the experience as "unbelievably itchy" with a feeling like "sharp itch that sometimes hurts underneath the skin, like you have something stuck under there but you can't get it out". This description effectively captures the mechanical nature of the irritation, as the microscopic barbed hairs physically embed themselves in the skin.
As symptoms progress, many individuals develop visible manifestations including welts, rashes, and in severe cases, small blisters. The skin between fingers proves particularly vulnerable to these effects, likely due to the thinner skin and difficulty in removing embedded hairs from these areas. Symptom duration varies dramatically, with mild exposures resolving in hours while more severe cases can persist for weeks. Several keepers report that symptoms can temporarily subside only to flare up again upon exposure to heat or when the affected area is scratched, suggesting the hairs remain embedded and active for extended periods.
Most concerning are the effects when urticating hairs contact sensitive tissues like the eyes, nasal passages, or lungs. Exposure to the eyes can cause significant pain, inflammation, and in severe cases, potential permanent damage including blindness. Respiratory exposure presents similarly serious risks, with keepers reporting immediate burning sensations in the throat and difficulty breathing following inhalation of airborne hairs. These risks highlight why many experienced keepers recommend protective equipment when working with species known for problematic urticating hairs.
An important factor affecting symptom severity appears to be repeated exposure. Unlike developing immunity, many keepers report that reactions to urticating hairs worsen with each subsequent exposure. As one source notes, "The effect of the hairs on your body will get worse, year by year". This progressive sensitization adds another dimension to understanding which species present the greatest long-term concerns regarding urticating hair severity.
Several factors beyond the specific tarantula species influence the likelihood and severity of urticating hair exposure. Understanding these risk factors enables tarantula keepers to develop effective protective strategies for minimizing exposure risks. Enclosure maintenance represents perhaps the highest-risk activity for urticating hair exposure. During substrate changes or enclosure cleaning, previously kicked hairs that have settled into the substrate can become airborne again, creating invisible clouds of irritating bristles. Species that kick hairs frequently as a defensive strategy, such as Lasiodora parahybana and Acanthoscurria geniculata, present particular risks during maintenance activities as their enclosures often contain substantial amounts of shed urticating hairs.
The webbing created by many tarantula species presents another significant risk factor. Species like Chromatopelma cyaneopubescens and the Avicularia group of Tarantulas incorporate urticating hairs into their extensive webbing. This incorporation of urticating hairs into webbing represents a passive defense strategy but creates significant exposure risks during routine care activities.
Tarantula size correlates positively with urticating hair severity, as noted by multiple sources. Larger species like those in the Theraphosa, Lasiodora, and Acanthoscurria genera not only possess intrinsically more irritating hair types but also have larger abdomens with more hairs to deploy. This size factor partly explains why the largest tarantula species consistently rank highest for urticating hair severity.
Keepers have developed numerous protective strategies to mitigate exposure risks. The most commonly recommended approach involves wearing personal protective equipment during high-risk activities. Safety glasses provide essential protection against eye exposure, while masks prevent respiratory exposure, and gloves protect the hands and wrists. Keep duct tape close by, this can aid in removing hairs, steroid cremes also work for affected areas. One keeper who experienced eye exposure to Theraphosa stirmi hairs reported needing three separate doctor visits to have the hair removed.
Handling techniques also play a crucial role in minimizing exposure risks. Using tools rather than hands whenever possible, working slowly to avoid startling the tarantula, and maintaining appropriate distance from species known for kicking hairs can significantly reduce exposure incidents. Some keepers recommend using springtails in enclosures to help process organic matter, reducing the frequency of needed maintenance and thus lowering exposure opportunities.
The examination of tarantulas with the most severe urticating hairs reveals a clear hierarchy dominated by the Theraphosa genus, followed closely by species in the Nhandu, Acanthoscurria, Lasiodora, Pamphobeteus, Xenesthis & Brachypelma genera. These findings have significant implications for both experienced tarantula enthusiasts and newcomers to the hobby.
For individuals considering which tarantula species to keep, awareness of urticating hair severity should factor prominently into decision-making. While species like Theraphosa stirmi might appeal due to their impressive size and feeding response, their exceptionally irritating urticating hairs present ongoing management challenges that should not be underestimated. Conversely, some New World species like Grammostola rosea possess relatively mild urticating hairs, potentially making them more suitable for keepers concerned about urticating hair reactions.
The progressive sensitization that many keepers experience with repeated urticating hair exposure warrants particular attention. Unlike many allergens where exposure can sometimes lead to desensitization, urticating hair reactions typically worsen over time. This pattern suggests that even keepers who initially experience minimal reactions should implement protective practices to prevent developing more severe reactions through cumulative exposure. It must also be mentioned that, the individual (keeper) may experience different reactions to different species. Like mentioned, the Grammostola Rosea has mild setae, although you could experience sever symptoms.
For the tarantula keeping community as a whole, continued documentation and sharing of experiences regarding urticating hair severity provides valuable practical knowledge. The variation in individual responses means that collective experiences offer the most comprehensive picture of which species present the greatest concerns. Through careful species selection, appropriate protective measures, and respect for these remarkable defensive adaptations, tarantula enthusiasts can minimize the risks associated with even the most severe urticating hairs while continuing to appreciate these fascinating arachnids.
All Scientific information came from:
PubMed/PubMed Central
PLOS ONE
American museum of national history digital library and
SciELO.
The keeper reports are from here and TarantulaForum.
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