10 Surprising Tarantula Facts

Tarantulas have an image problem. Most of what people assume about them comes from horror movies rather than biology. Here are ten facts that paint a very different picture.

1. Females can live decades longer than males. A female Mexican red knee typically lives 25 to 30 years, while a male rarely passes 10: once mature he stops molting and does not last long after.

2. Their blood is blue, not red. Like other arthropods, tarantulas use copper-based hemocyanin to carry oxygen instead of the iron-based hemoglobin found in vertebrates, which gives their blood a blue tint. Some are blue on the outside too, and that blue is not pigment. It comes from nanostructures in the hairs that scatter light. Distantly related tarantulas arrived at nearly the same shade, peaking within a narrow band around 450 nanometers, by several different structures. Tarantulas see color poorly and do not court with visual displays, so the blue is probably not for attracting mates.

3. They "hear" through vibrations, not ears. Tarantulas lack ears entirely and instead sense their environment through tiny sensory hairs on their legs that detect vibrations in the ground and air.

4. Their main defense usually isn't biting. Many New World tarantula species kick urticating hairs from their abdomen when threatened, which cause intense itching, rather than relying on their bite as a first line of defense. None of it helps against their worst enemy. A female tarantula hawk wasp enters a burrow, chases the spider into the open and stings it into permanent paralysis. She lays a single egg on its abdomen and seals it in, and the larva feeds on the living spider, avoiding the vital organs to keep it alive as long as possible.

5. All tarantulas produce silk, not just web-builders. Even species that don't spin prey-catching webs use silk to line burrows, wrap egg sacs, and create drop-lines, silk plays a role in nearly every tarantula species' life regardless of hunting style.

6. Some species can go over a year without eating. Tarantulas have remarkably slow metabolisms, and healthy adults, especially during premolt, can fast for extraordinarily long stretches without harm. Slowing the metabolism to a crawl is an invertebrate specialty, and tardigrades take it furthest, shutting down almost completely for decades before rehydrating.

7. The largest species by mass has a leg span near a foot. The Goliath birdeater, native to South America, is among the largest tarantulas in the world, with a leg span that can approach 11 to 12 inches.

8. Despite the name, they rarely eat birds. "Bird-eating" spiders got their name from a rare historical account, but their actual diet is overwhelmingly insects, and occasionally small vertebrates like lizards or frogs for the largest species.

9. A short fall can be more dangerous than a bite. A tarantula's exoskeleton is surprisingly fragile against impact, and a fall from even a modest height, like off a keeper's hand, can rupture the abdomen and be fatal, making drop injuries one of the leading causes of death in captivity.

10. Molting lets them regenerate lost limbs. A tarantula that loses a leg to injury or a failed molt can regrow it over subsequent molts, gradually restoring it to near-normal size and function. It is also why a tarantula that goes still and stops eating is usually preparing to molt, not dying.

Which fact surprised you the most? Let me know in the comments.

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