Animal Sex: How Tarantulas Do It
When mating, tarantulas like these Mexican fire leg tarantulas (Brachypelma boehmei) face each other and elevate their bodies and legs.
Credit: skydie / Shutterstock.com

With their hairy bodies and large fangs, tarantulas are one of the most recognizable and feared types of spiders in the world. Though their fearsome appearance actually belies a gentle nature — they're non-threatening to people and are popular pets throughout the world — does this temperament also extend to their partners during mating?

Tarantulas belong to the Theraphosidae family of arachnids and are the largest and longest-living spiders in the world, according to a 2013 review in the journal Arachnology. (Find out why some spiders in this family turn blue.)

These spiders, of which there are nearly a thousand species alive today, generally mate in the spring and summer; but some species are known to mate only in the winter, said Nelson Ferretti, a tarantula expert with the the National Scientific and Technical Research Council in Argentina and lead author of the review.

Once males reach adulthood, they "charge" their two pedipalps, or palps — small appendages near the front of their head — with sperm. That is, they will spin a small "sperm web," deposit sperm onto it, and take up the sperm into specialized storage structures of the palps, called palpal bulbs.

Charging their palps is energetically costly, but males can typically copulate with numerous females with a single charge, explained study co-author Fernando Pérez-Miles, an entomologist at the University of the Republic in Uruguay.

Finding and courting mates

During the mating season, charged males will go out in search of receptive females by zeroing in on their pheromones, or chemical scents, though it's unclear if only receptive females produce male-attracting pheromones.

"We have seen under laboratory conditions that males court on silk threads of virgin, young, old or copulated females," Ferretti told Live Science. "But females that are not receptive do not leave the burrow or they even expel males through aggression."

Surprisingly, if two male tarantulas come across a single female, they don't appear to show the competitive aggression toward each other that's known to be common in other animals. Ferretti has only seen a confrontation between two male tarantulas, but instead of fighting they tried to mate with each other before going about their separate ways peacefully, he said.

When a male finds a receptive female, the pair will engage in a courtship ritual.

Depending on the species, males may engage in a range of different moves, the most widespread being papal drumming (alternating taps on the female's silk threads or the ground with his padipalps) and body vibrations (high-frequency movement of the legs that also transmits seismic signals).

These behaviors likely inform the female about the quality of the male and his species, Pérez-Miles told Live Science, adding that the latter information is sometimes lost in translation (though different species aren't known to copulate).

If the female likes what she feels, she'll respond by tapping her front legs or palps to let him know she accepts him and possibly to direct him toward her burrow. In some species, the female will simply leave her burrow and head toward the male instead.

Careful copulation

To mate, the pair will orient themselves face-to-face with their bodies and front legs elevated.

In some species, the male will perform spasmodic beats on the female with his second pair of legs after coming into contact with her, a behavior thought to relax the female's fangs. In most species, males have specialized spurs that they use to clasp the female's fangs, helping them both elevate their mates to the right immobilizing position and prevent possible bites.

Males of one Brazilian species, Sickius longibulbi, take things a step further by pushing their mates all the way over and onto their backs.

Once in position, the male will insert his charged palps into the female's genital opening one to five times, before leaving to find other mates — if he's lucky enough to avoid getting eaten, which is common. [Why Some Female Spiders Eat Males Before Mating]

Importantly, sexual cannibalism in tarantulas probably has nothing to do with hunger level, and instead occurs if the male tries to approach the female without courting, enters her burrow too abruptly, or doesn't leave quickly enough after mating, Ferretti said.

Usually, however, mating leaves the female immobile for a brief time, allowing the male to get away if necessary, at least in the wild. "Sexual cannibalism is really rare in tarantulas, and probably due to captivity conditions of observation," Pérez-Miles said.

Editor's Note: This article was updated to correct the university affiliation of Fernando Pérez-Miles.

Follow Joseph Castro on Twitter. Follow us @livescience, Facebook & Google+.