Mexican Red-knee Tarantula (Brachypelma smithi)

I haven’t written about a spider in a while, mainly because I’ve started drawing all the animals I write about. Spiders are absolutely terrifying, so drawing them is super difficult for me. But they are also really cool, so I bit the bullet this week and picked a spider for today’s post. I chose a tarantula because they’re a little less frightening than most spiders, mainly because they are kind of furry, and fur makes animals cuter.

Mexican red-knee tarantulas are aptly named, both for their red knees and because they are found in Mexico. More specifically, they live in southwestern Mexico. They are primarily found in dry areas, such as scrubland, deserts, dry thorn forests, or tropical deciduous forests. Red-knee tarantulas hide out in burrows, which are constructed at the base of thorny plants like cacti.

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A female red-knee tarantula. Females are bulkier than males, though males have longer legs. Image credit: George Chernilevsky via Wikipedia

Being tarantulas, these spiders are pretty big. They range in size from 12 to 14 cm, with males having a smaller mass than females. They are mostly black, with red-orange joints on their legs. Their abdomens are covered in brown hairs, which is the only thing that makes red-knee tarantulas somewhat acceptable to look at.

These hairs are not to be taken lightly, however. When threatened, red-knee tarantulas can eject the hairs from their abdomen at any predators. The hairs are barbed and can get stuck in skin or eyes, causing irritation and discomfort. Tarantulas do have venom, though it only has mild effects on humans, and red-knee tarantulas are quite calm and rarely bite people.

To further avoid predation, red-knee tarantulas spend much of their time in their burrows. The burrows are quite simple, consisting only of a tunnel and one or two chambers. One chamber is used for moulting, and the other for resting and eating. Tarantulas are ambush predators, waiting until an animal walks across the webs at the front of their burrows. When prey is detected, the spider emerges and holds down the prey with its front two legs, biting the victim to paralyze and liquefy it. Red-knee tarantulas feed on insects, frogs, and mice.

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A nice close up of a red-knee tarantula. Image source

Mating in red-knee tarantulas is a somewhat violent affair. Males begin by placing sperm on a special web outside a female’s burrow. The two spiders face each other while the female opens her jaws. The male then locks her jaws in place with special hooks on his front legs, and the two spiders rear up. The male then pushes the female backwards and picks up his sperm and transfers it to an opening on the female’s abdomen. Then comes the really tricky part: the male releases one of the female’s fangs and then prepares for a hasty retreat before fully letting her go, as females can be quite aggressive after mating.

Female tarantulas lay 200 to 400 eggs on a silk mat, and then deposit a liquid containing sperm onto the eggs. They then wrap their eggs in silk and carry them until they hatch, for about one to three months. The spiderlings are independent two weeks after leaving the eggs, though they do not reach sexual maturity for a number of years.

Red-knee tarantulas grow through a process called moulting, where they shed their skin, as their exoskeleton does not stretch and thus does not allow room for growth. Spiders are most vulnerable during moulting, and so they retreat into their burrows to complete the process. Red-knee tarantulas stop eating before their moults, and become sluggish. They also cannot eat for days or weeks after moulting, as their fangs are too soft to capture prey. It doesn’t sound like a very fun way to grow, but it works for spiders.

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My fun drawing of a red-knee tarantula. I was away and only had a four-coloured pen, so I couldn’t get the knees as orange as I would have liked, but she still looks pretty cool! 

Due to their docile nature and striking (though terror-inducing) appearance, red-knee tarantulas are quite popular in the pet trade. They were once caught in large numbers for export, but they have since been bred in captivity, so most specimens are now captive-bred. Habitat destruction is another threat to these lovely, gentle spiders, and they are currently listed as Near Threatened. I’m no fan of spiders, but I definitely don’t want to see any go extinct. If one enters my house, I kill it (I don’t even want to think about what I’d do if a tarantula wandered into my room), but I’m perfectly happy with spiders living happily in the wild, preferably in a country very far away from me.

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