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More than a few tourists in northern Chile or coastal Peru has woken up to find an unwelcome visitor on their pillows. The Peruvian green velvet tarantula, also known by its scientific name, Thrixopelma pruriens is one of three species of a genus of "colorful" tarantulas that inhabit South America. The Peruvian green velvet tarantula earns its scientific epithet "pruriens," or "itchy," by its habit of throwing its hair at potential predators, tiny daggers at the end of the hair releasing a compound that causes itching. This skill can give the spider a chance to escape getting swatted by hapless humans who encounter it on their pillows, in the bathroom, or on the breakfast table, as its victims rub their skin or eyes.
Unlike other closely related South American spiders, the Peruvian green velvet tarantula isn't especially brightly colored. Its velvety hairs do look green if you look closely enough (assuming the spider will allow you to look closely enough), but from a few feet away this spider looks a dull brown with beige stripes on its legs. This spider is much less likely to be collected by tarantula enthusiasts than the more brightly colored tarantulas from Brazil and Venezuela. What makes the Peruvian velvet tarantula stand out is the venom in its hairs, which has the unusual ability to block chronic pain.
A Different Kind of "Toxin"
Many snakes, cone snails, and spiders have toxic venoms that they can release with a bite. These venoms can make humans very sick or even kill. Peruvian green velvet tarantula venom (the kind released in a spider bite, not the kind in the spider's hairs) is also potent, but it acts as an anesthetic. Most kinds of poisonous creepy crawlies release venom that stops nerve transmissions. The venom from the Peruvian green velvet tarantula specifically stops pain transmissions.
The toxin in this species of spider is a compound called ProTx-II. This chemical, for reasons not currently known, tends to concentrate in the membrane surrounding neurons that send pain messages to the brain. It has exactly the right geometry to fit like a key in a lock in receptors that would otherwise instruct the neuron to send pain signals to the rest of the central nervous system.
Why Would Anyone Be Interested in "Toxic" Pain Relief?
There are good reasons that researchers at the University of Queensland Institute for Bioscience, where the Peruvian green velvet tarantula's venom is being analyzed, are enthusiastic about this discovery. Many people suffer neuropathic pain. This pain is caused by injury to nerves by high blood glucose levels in uncontrolled diabetes, chemotherapy, mechanical injury, or certain kinds of viral infections (such as herpes and HIV). There are very few medications for this kind of pain that don't cause extreme drowsiness, and usually weight gain. A medication made from the this tarantula's venom might be one more weapon in modern medicine's very limited arsenal of effective medications for dealing with neuropathic pain. The toxin might also be adapted to treating chronic muscle tension in multiple sclerosis and high blood pressure.