Mexican Red-Knee Tarantula: Facts, Habitat and Lifespan

Appearance: black legs with orange knees

The Mexican red-knee tarantula is a heavy-bodied spider covered in fine hairs. Its legs are black to reddish black, with three colored rings on each: deep orange on the “knee” (the patella), pale orange-yellow on the lower leg (the tibia) and a creamy band further down. The orange knees give the species its name.

The carapace, the shield over the front body section, usually has a dark central patch and a pale, pinkish to orange border. The abdomen is black and covered with long brownish hairs. Some of these are urticating hairs, special barbed hairs used for defense.

Males and females look similar, but adult males have longer, thinner legs and a smaller abdomen, and they carry hooked spurs on their front legs and swollen tips on their pedipalps (the leg-like feelers at the front) used in mating.

A name shared by two species

For decades, almost all Mexican red-knee tarantulas were called Brachypelma smithi. In 1994 a scientist redescribed B. smithi using specimens that actually belonged to a different species. Brachypelma hamorii had been described separately in 1997, but the confusion continued until 2017, when Mexican arachnologists Jorge Mendoza and Oscar Francke sorted out the two species using anatomy and DNA barcodes.

Both species look almost identical and are both called Mexican red-knee tarantulas. They live on opposite sides of the Balsas River basin: B. hamorii to the north, B. smithi to the south, mainly in Guerrero. They are told apart by details of the male palpal organs and female reproductive structures. Many older books, websites and photos labeled B. smithi actually refer to B. hamorii.

How big is a Mexican red-knee tarantula?

This is a large tarantula, though not a giant like the Goliath birdeater of South America.

Females have slightly longer bodies and much heavier abdomens. Males have slightly shorter bodies but longer legs, which helps them walk long distances in search of females.

Habitat and range

Brachypelma hamorii is found only in western Mexico, on the Pacific-facing slopes of the Sierra Madre Occidental and Sierra Madre del Sur in the states of Colima, Jalisco and Michoacán. Its natural habitat is hilly tropical deciduous forest, a dry forest whose trees lose their leaves in the long dry season, along with thorn scrub and grassy clearings.

Each tarantula lives in a burrow that it digs or extends under a log, rock or tree roots, often among thorny shrubs and tall grass. A typical burrow has a single entrance only slightly wider than the spider, a tunnel and one or two chambers. One chamber is large enough for molting, and a deeper one serves as a resting and feeding room. Silk lines the entrance and walls.

Females spend most of their lives in or near the same burrow. When molting or guarding eggs, they seal the entrance with silk, sometimes mixed with soil and leaves.

What do Mexican red-knee tarantulas eat?

Like other tarantulas, it is a sit-and-wait predator. At night it waits at or near the burrow entrance and grabs passing prey, mostly large insects such as crickets, grasshoppers, beetles and cockroaches. Large tarantulas in general may occasionally take small frogs or lizards.

Tarantulas do not catch prey in webs. They detect vibrations with sensitive hairs on their legs, seize the prey with their front legs and bite with their fangs, injecting venom that paralyzes the prey and begins digestion. The spider then crushes and sucks up the liquefied food. Like many spiders, it can survive long periods without eating.

Behavior and defense

Mexican red-knee tarantulas are solitary and mostly nocturnal. They are generally calm and slow to bite. When threatened, a red-knee typically raises its front legs in a warning posture or turns away and uses its back legs to flick a cloud of urticating hairs from its abdomen. These hairs can irritate the skin, eyes and airways of a predator, or a person.

Its venom is mild for people compared with that of dangerous spiders, but the large fangs can give a painful bite, and allergic reactions are possible. Bites are rare and usually happen when a spider is handled. The safest approach is simply to admire tarantulas without touching them; anyone who has a serious reaction to a spider bite should seek emergency medical help immediately.

Its natural enemies include white-nosed coatis, birds, lizards and snakes. Females of spider-hunting wasps called tarantula hawks paralyze tarantulas and lay an egg on them, so the wasp larva can feed on the living spider.

How a tarantula senses its world

Despite having eight small eyes grouped on a mound at the front of the carapace, a tarantula sees poorly. It can probably tell light from dark and detect movement, but little more. Instead, it relies on touch and vibration. Thousands of fine sensory hairs on its legs and pedipalps pick up air currents and ground vibrations, and slit-shaped sense organs in the exoskeleton register tiny strains, so the spider can feel an insect walking near its burrow.

Tarantulas breathe through two pairs of book lungs, stacks of thin, leaf-like plates on the underside of the abdomen. Like other spiders, they extend their legs partly by hydraulic pressure, pumping body fluid into the limbs, while muscles bend them. Each foot ends in two claws and dense tufts of hair that help the spider grip rough surfaces.

Seasons in the dry forest

Western Mexico has a long dry season in winter and spring and a rainy season in summer and fall. During the hottest, driest months, red-knee tarantulas stay deep in their burrows, where the air is cooler and more humid, and may close the entrance with silk.

The rains bring a burst of insect life and the main period of activity. This is when mature males leave their burrows and roam in search of females. Most tarantulas seen crossing roads and paths are wandering males.

Reproduction and life cycle

Mating takes place mainly in the rainy season, roughly July to October. A mature male first spins a small sperm web, deposits sperm on it and loads it into his pedipalps. He then searches for a female’s burrow and taps signals at the entrance. During mating, he uses the hooks on his front legs to hold the female’s fangs away, transfers sperm and then retreats quickly, since females can be aggressive after mating.

The female stores the sperm until the following spring. She then spins a silk mat, lays some 200 to 400 eggs on it, wraps them into an egg sac and guards it in her burrow, turning it to keep it at the right temperature and humidity. The eggs hatch after roughly two to three months, and the young spiderlings disperse a few weeks later.

Growth is very slow. Spiderlings molt every few weeks at first and less often as they grow. You can read how this works in how do tarantulas molt? In the wild, males reach maturity at about four to five years, while females mature later, at around six to seven years or more.

How long do Mexican red-knee tarantulas live?

The Mexican red-knee is one of the longest-lived spiders. Females are reported to live about 25 to 30 years, figures based mainly on spiders kept in captivity. They keep molting as adults, which lets them replace damaged parts.

Males have much shorter lives. After their final molt into adulthood, they stop molting, wander in search of females and usually die within a year or so. Their total lifespan is typically around five years and rarely more than ten. The reasons for this difference are explained in how long do tarantulas live?

Conservation status and trade

The IUCN Red List assessed Brachypelma hamorii as Vulnerable in 2019. It has a small range in western Mexico, and its dry forest habitat is being cleared for farming, grazing and development. Some local people also kill tarantulas out of fear.

The species’ bright colors and calm nature made it one of the most popular tarantulas in the international pet trade. Large numbers were once exported from Mexico. In 1985, the Mexican red-knee (then called B. smithi) became one of the first spiders listed on CITES Appendix II, which controls international trade, and all Brachypelma species were added in 1994.

Today many red-knee tarantulas sold abroad are bred in captivity, but smuggling of wild-caught spiders still occurs. Because females take years to mature, populations recover slowly from collecting.

Myths and facts

Myth: tarantulas are deadly. The Mexican red-knee’s venom is not dangerous to healthy people. Its bite is usually compared to a bee sting, and the main nuisance for people is the irritating hairs. See are tarantulas dangerous? for the full picture.

Myth: tarantulas spin webs to catch prey. They use silk to line burrows, make sperm webs and egg sacs, and seal their homes, but they hunt by ambush.

Fact: the shed skin is not a dead spider. A molted tarantula skin is a complete hollow copy of the spider, including its fangs and leg hairs, and is often mistaken for a dead tarantula.