Tarantulas have beneficial partnerships with other species

A recent study has explored the ecological relationships and evolutionary adaptations of tarantulas, uncovering surprising details about these often-feared spiders. 

The research revealed that tarantulas frequently form mutually beneficial partnerships with various species, including amphibians, reptiles, and even army ants – predators typically known to feed on spiders. 

Notably, the study suggests that the dense hair covering tarantulas may have evolved as a defense mechanism against these predatory ants.

Tarantula partnerships with other species 

An international team of scientists conducted an extensive literature review and examined how tarantulas interact with other species. 

This study is the first to report associations between tarantulas and animals such as snakes, whip spiders, and harvestmen. Additionally, the researchers documented over 60 new cases of partnerships between tarantulas and amphibians from ten different countries.

According to the experts, the interactions and even cohabitation between tarantulas and other species are often mutually advantageous.

“Apparently, the frogs and toads that live within the retreats of tarantulas benefit from the shelter and protection against their predators. In turn, they feed on insects that could be harmful to the spider, its eggs, and its juveniles,” said lead author Alireza Zamani, a biologist at the University of Turku, Finland.

“It seems that tarantulas might not be as scary and threatening as their reputation suggests.”

Why are tarantulas so hairy?

One of the most significant insights from the study is the proposal of a new hypothesis regarding why tarantulas are so hairy. The researchers posit that the hirsuteness – or hairiness – of tarantulas may have evolved as a defense mechanism against predatory ants.

“Observations indicate that army ants tend to ignore both adult tarantulas and spiderlings. This is quite interesting, since army ants are known to attack and feed on a wide variety of arthropods,” Zamani said.

The study observed that ants interacting with tarantulas would enter the spider’s burrow, gather food remains, and clean the burrow, which benefits the tarantula. Only a few ants attempted to attack the spiders, but these attacks failed because the tarantulas’ legs were protected by a fringe of stiff hairs.

Evolutionary strategies of tarantulas 

“The dense hair covering the tarantula’s body makes it difficult for the ants to bite or sting the spider. Therefore, we believe that hairiness may have evolved as a defense mechanism,” said Zamani. 

This hypothesis is supported by findings that many burrowing New World tarantulas cover their egg sacs with urticating hairs, Zamani noted. 

Barbed hairs for defense 

“The tarantulas typically release these barbed hairs as a defense mechanism, deterring and sometimes even killing their attackers. Covering their egg sacs with these hairs, however, effectively hinders the movement of small injurious arthropods, such as ants, that might try to attack the eggs.”

The study also suggests that the hirsuteness of tarantulas could be a trait that is still evolving and may be more developed in certain tarantula species. Spiders with less dense body hair could be more vulnerable to ant attacks.

Evading predatory ants 

In addition, the researchers documented a unique escape strategy employed by New World arboreal tarantulas when threatened by ants.

“In a field study in Peru, a female Avicularia hirschii was observed leaving its silken retreat and hanging from the edge of a leaf by the tips of its front legs after sensing the approach of army ants in search of live prey,” Zamani recounted.

Defensive secretions

The scientists also proposed that tarantulas might have another defense strategy involving a previously unknown chemical mechanism. They suggest that tarantulas may possess specialized epidermal glands in their cuticles that could secrete predator-repellent substances.

“This hypothesis is supported by the observation that cats and dogs, animals with highly developed sense of smell, tend to wince and move away after sniffing a tarantula. Tarantulas have slit-like epidermal gland openings of unknown function, which may produce defensive secretions responsible for this reaction,” Zamani said.

While more evidence is needed to confirm the chemical defense mechanism hypothesis, this study represents a significant advancement in understanding the behavior of tarantulas, including their surprising partnerships.

The study is published in the Journal of Natural History.

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