Predators
Regardless of their fearsome reputation, tarantulas are themselves an object of predation, the most specialized of these predators are large members of the wasp family Pompilidae. In the Americas, these insects are termed "tarantula hawks", being parasitoids of tarantulas. The largest tarantula hawks, such as those in the genus Pepsis, will track, attack and kill large tarantulas. They use olfaction to find the lair of a tarantula. The wasp must deliver a sting to the underside of the spider's cephalothorax, exploiting the thin membrane between the basal leg segments. This paralyzes the spider and the wasp then drags it back into its burrow before depositing an egg on the prey's abdomen. The wasp then seals the spider in its burrow and flies off to search for more hosts. The wasp larva hatches and feeds on the spider's non-essential parts and, as it approaches pupation, it consumes the remainder. In addition to more mundane cuisine, tarantulas are considered a delicacy in certain cultures (e.g. Venezuela and Cambodia). They are usually roasted over an open fire to remove the hair and then eaten.
Some other arthropods, such as giant centipedes are also known to prey on tarantulas.
Besides the normal "hairs" covering the body, some tarantulas also have a dense covering of irritating hairs called urticating hairs, on the opisthosoma, that they sometimes use as protection against enemies. These hairs are present on New World species but not on specimens from the Old World.
Urticating hairs are usually kicked off the abdomen by the tarantula, but it is noteworthy that some may simply rub the abdomen against the target, such is so with the Avicularia genera. These fine hairs are barbed and serve to irritate. They can be lethal to small animals such as rodents. Some people are extremely sensitive to these hairs, and develop serious itching and rashes at the site. Exposure of the eyes and respiratory system to urticating hairs should be strictly avoided. Species with urticating hairs can kick these hairs off: they are flicked into the air at a target using their back pairs of legs. Tarantulas also use these hairs for other purposes such as to mark territory or to line their shelters (the latter such practice may discourage flies from feeding on the spiderlings). Urticating hairs do not grow back, but are replaced with each moult. The intensity, amount, and flotation of the hairs depends on the species of tarantula. Many owners of Goliath Birdeaters (T. blondi) claim that theraphosids have the worst urticating hairs.
To predators and other kinds of enemies, these hairs can range from being lethal to simply being a deterrent. With humans, they can cause irritation to eyes, nose, and skin, and more dangerously, the lungs and airways, if inhaled. The symptoms range from species to species, from person to person, from a burning itch to a minor rash. In some cases, tarantula hairs have caused permanent damage to human eyes.
Some setae are used to stridulate, which makes a hissing sound. These hairs are usually found on the chelicerae. Stridulation seems to be more common in old-world species.
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