An Introduction to Tarantulas

Having talked about bugs and reptiles, I have only grazed the surface of kept animals that give common people the willies.

Few creatures on earth inspire undeserved fear than do spiders, and among spiders tarantulas stand as exemplars of terror. This is, of course, due to a lack of education among the masses, with a hearty supplement from media exploitation. Films are especially guilty of spreading misinformation and fear about spiders, and while fantasy is wonderful, when people don't know fact from fiction innocent creatures suffer. Such was the fate of sharks after Jaws, and spiders after Arachnophobia. Both are movies I enjoy watching, but abhor for the damage they've done to their associated animals.

In an effort to undo some of the harm that lack of education has done to tarantulas, I'm going to offer a primer on the large spiders.

First, what makes a tarantula?

Tarantulas are large spiders of the Theraphosidae family. They have bristly hairs on their abdomens and legs, and possess the dreaded eight eyes of most spiders, although often only two are visible to the naked eye. Tarantulas have downward pointing fangs on adapted front appendages called chilicerae, which are used for first nabbing and envenomating prey, and then crushing the meat to a pulp between the two chilicerae to be slurped in by their sucking mouthparts.

Like all arachnids, spiders have four pairs of proper legs. In some species the legs are stubby, while others may be quite long and thin. Many species of tarantulas are sexually dimorphic in the length of their legs in proportion to their bodies; females will have stockier bodies and shorter legs, while males appear more spindly-limbed. Male tarantulas have hooks on the tibial segment of their legs, which are used to hold the female's fangs during mating.

Between the chilicerae and front pair of legs, tarantulas possess appendages called pedipalps that resemble a fifth pair of short legs. These are used to sense their environment and help in holding prey, and in males they have been adapted to be used as the tarantula's inseminating organs. Some day I'll delve into the fascinating bedroom antics of tarantulas.

Like all other spiders, tarantulas have two body segments: the prosoma and opisthosoma. The prosoma is the front portion where the chilicerae, pedipalps, and legs attach, and also houses the tarantula's brain, mouthparts, and sucking stomach. The opisthosoma is little more than a gooey sac wherein lie the book lungs, heart, reproductive organs, and spinnerettes. Tarantulas generally have two pair of spinnerettes, which are adapted limbs used to spin silk. In some species only one pair may be visible.

New World species of tarantula possess urticating bristles on the opisthosoma. These are tiny, barbed hairs that can be flicked off in a cloud when the tarantula is threatened. The tiny hairs cause minor irritation to exposed skin, but wreak havoc on mucous membranes and the eyes. They can cause severe damage in the eyes, including blindness, and are easily the best defence available to tarantulas. Thankfully these New World species are generally rather calm, and not prone to firing off a cloud of bristles without provocation; when they do the furious motion of the back legs is easily distinguished, and a clear sign to stay back until the hairs have settled.

Old world species have not evolved this bristly defence, and seem to make up for it with a heightened aggression and flagrant displays of hostility. These are truly fractious much of the time, and should generally be operated around with greater care than their New World cousins.

Now that we have a basic understanding of tarantulas, let's dispel some misconceptions.

Tarantulas are NOT poisonous. This is really just a pet peeve of mine, but poison is ingested, while venom is injected. Some use poison to cover any sort of toxin, but I'm a stickler for semantics. Y'know, when I'm not intentionally abusing words.

Tarantulas, like nearly every species of spider, are venomous. That said, a tarantula bite will not kill you. Most species of tarantula will only use their venom on prey, while their defensive bites lack venom, so called "dry bites". If a tarantula were to envenom you, the result would more than likely consist of mild pain, possibly coupled with a burning or numbing sensation in the affected area. Throbbing pain is not unheard of, so while tarantula bites are not fatal, they still have the potential to really suck.

Generally the larger a tarantula is, the less pleasant their bite will be. This is due less to the potency of their venom, and more to how much venom they are able to inject, and also because of the tissue damage possible from their fangs. A tarantula over five inches is likely to cause medically significant mechanical damage. The largest tarantula species can have fangs over an inch long, and can easily inflict bites requiring stitches.

Size is another area where tarantulas are often exaggerated. The largest species of tarantulas, the so-called bird eaters, include Lasiodora spp and Theraphosa spp. These tarantulas average between eight and ten inches of legspan, although fourteen inch specimens have been known of Theraphosa blondi. Even the largest of these are unlikely to have bodies larger than eight inches long. By contrast the largest true spider has a legspan of about eleven inches, with a tiny body of three inches or so.

This is a sampling of nifty things regarding tarantulas, and while I have more in mind (mating habits especially), I'm going to stop there for now. Let me know if there are any other myths or facts you'd like addressed.

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