Tarantulas are the largest members of the spider family. Spiders have existed for over 300 million years and are thought to be one of the most successful of creatures on Earth. There are over 35,000 species of spiders, of which the tarantulas make up about 800.
Like all spiders tarantulas have eight legs. The Goliath Tarantulas can have as large as a ten inch leg span and are considered a delicacy to the Piaroa Indians of Venezuela. Before they are eaten, however, their great fangs must be removed. (The fangs are used later as toothpicks to pick the exo-skelleton in the diner's teeth.)
Spiders themselves may consume insects or other small prey. The large tarantulas of South America are known to prefer small lizards and snakes and will also dine on small mamals. Tarantulas, like all spiders are meat eaters. However, tarantulas do catch their prey in webs as many other spiders do. But they do find a likely spot, sit, and wait. When something appears, they put on a burst of speed, grab the victim with some combination of their eight legs, and then inject an imobilizing venom. Prey is usually eaten directly. The tarantula abdomen can hold a tremendous amount of food, and once it has feasted a tarantula can go up to several months without eating again.
Like insects, spiders in general have a head, abdomen and thorax. But the head and thorax are combined into something called a cephalothorax. Spiders lack the compound eyes and antennae of insects. In the place of antennae they have feelers protruding from their mouth or use their leg hairs to sense out their surroundings. They have eight single eyes arranged on their heads to help them see in many directions. In spite of their many eyes, tarantulas do not see all that well (though some spiders, such as the jumping spiders have excellent vision).
Tarantulas, such as the red-knee found in the Mexican rain forests, burrow into the ground and line their tunnel with silk from their spinerets. They are generally solitary creatures, only coming together to mate. The male carries his sperm on his feelers (pedipalpi) which he endeavors to inject into some openings in the female's abdomen. He does this as quickly as possible and then retreats, hopefully (for him) he escapes before the female can make a meal of him. For this reason, the male has a much shorter lifespan (a tentative ten years) than the female (up to 30 years).
The breathing and circulation systems of the tarantula, as in other spiders, are comparitively cumbersome. Tarantulas breathe through a small opening in their abdomen, taking air to their "book-lungs" (so called because of their shape). This is where oxygen is transfered to its blood. But the spider's big heart has to work over-time to meet the needs of the body in stressful circumstances. The muscles in the "knees" of spiders in general only contract, to make the legs extend again requires fluid pressure from the circulatory system. This inefficient system means that when in motion the spider's heart rate and blood pressure increase dramatically. Spiders will therefore tire quickly and will collapse if forced to run for more than a minute or two.
Tarantulas get their name from the city of Taranto in Italy. Beginning in the year 1370 and for about three hundred years thereafter there was an epidemic of spider bites durring the harvest season in the farming areas around the city. The bites were thought to be produced by the "tarantula". The only cure for the bite was supposed to be to dance vigorously in a gyration called the tarantella. Those bitten were called called the tarantati. Paul Hillyard in "The Book of the Spider", tells us that those bitten suffered "severe pain and swelling, muscle spasms, vomiting, palpitation, fainting, priapism (involuntary erections), shameless exhibitionism, acute melancholia, and delirium, leading to death if untreated."
It turns out that the likely culprit was not the tarantula, but another more reclusive spider that also lurked in the fields. Although the bite of the tarantula can be painful, it does not usually result in death (though it can). The Red Knee Tarantula is the one that is commonly seen in the movies and kept as a pet. Of all the tarantulas it tends to be the least antagonistic to humans.
Interesting Link: Tarantula Woodkits