What was found
Researchers placed New World tarantulas in controlled encounters with ants and recorded the spiders deliberately directing urticating setae toward the attackers. The hairs interfered with the ants and helped protect vulnerable areas of the spiders' bodies.
Urticating setae are famous as a defence against vertebrates, but this is the first experimental report of tarantulas actively deploying them against invertebrate attackers.
What makes that interesting
Ants are small, but a coordinated group can be a serious threat. The experiment shows that a defence often explained mainly in terms of mammals, birds, or reptiles can also work at a completely different scale.
The paper also fits with broader observations that dense tarantula setae can impede ants. Active deployment gives that protective relationship a behavioural component, rather than making it only a passive hairy barrier.
Why it matters
The finding expands the known function of urticating setae and supports a provocative evolutionary possibility: pressure from ants may have helped shape this defence. That remains a hypothesis about evolutionary history, not something one experiment can prove, but it is now a much stronger question to investigate.