People do love their pets. Some people bring dogs into their families and others prefer cats. And then there are the people who love their spiders. Many spider-lovers have a soft spot for tarantulas, big, hairy creatures that don’t have venom. And because tarantulas are usually docile — which means they’re calm and not mean — some people even buy them for children.

If you’re contemplating taking home a tarantula, however, first think about the recent case of a 29-year-old tarantula owner in England. It may show why these spiders make lousy pets. He had conjunctivitis in his right eye, which means the membrane that surrounded his eyeball had become irritated.

Some types of tarantulas seem docile, but they do have ways of defending themselves.

website of the Albuquerque, N.M., Biological Park

His doctors were puzzled because the swelling wasn’t responding to medicine, so they took a closer look at the eyeball. In a recent study, the doctors reported seeing “fine hair-like projections” sticking out of the man’s eye. When told about his hairy eye, the man knew exactly what the fine hair-like projections were: tarantula hairs.

The story of the man with tarantula hairs in his eye is an example of a case study. This particular case study appeared in a recent issue of a medical journal called The Lancet. In a case study, researchers — in this case, the man’s doctors — report on something interesting that happened to one or just a few people.

By sharing these stories of unusual cases, researchers can gain experience from each other that may make them better scientists. (After reading this report, for example, a doctor might think to ask a patient showing symptoms of conjunctivitis whether or not he owns a pet spider.) The researchers who reported this study were Jonathan Norris, Zia Carrim and Andrew Morrell.

In this case study, the tarantula owner told his doctors about something that happened as he cleaned the spider’s home. He was trying to remove a stubborn stain when he saw the tarantula move. He turned to look at the spider, and the spider “released ‘a mist of hairs’ which hit his eyes and face.” Some of these hairs, which can have sharp points called barbs, stuck deep into his eyeball. These barbed hairs were what the doctors saw. The doctors couldn’t remove the hairs, so they prescribed eyedrops containing a strong medicine. After eight months, the man’s eye still wasn’t completely healed — but he did start to wear eye protection when he cleaned his spider’s home.

This case study isn’t the first showing how tarantulas may be bad for the eyes. In 1997, a report in the journal BMJ (which used to be called the British Medical Journal) described three patients with “itchy, gritty, red eyes.” Guess what? These three people had also crossed paths with irritated tarantulas. One of the patient’s eyes didn’t heal for three years. The other two were still experiencing irritation in their eyeballs 2 to 6 years later. The researchers reported that the inflammation, or swelling, caused by tarantula hairs could lead to other more serious problems such as cataracts. Cataracts are cloudy areas on the eye lens that affect vision.

In 2003, a report in the journal Eye told the story of a 14-year-old boy who had also received an eyeful of tarantula hairs and been bitten. But he loved his pet spider even though it hurt him, and his family told the doctors that they would be keeping the tarantula.

There’s no explaining why people love particular kinds of animals. But people who decide to keep tarantulas should be prepared to handle their beloved pets with goggles and gloves — and should probably leave them at home on “Show and Tell” day.

POWER WORDS (adapted from the Yahoo! Kids Dictionary)

case study A detailed analysis of a person or group, especially as a model of medical, psychiatric, psychological or social phenomena.

inflammation A reaction of tissue to irritation, injury or infection, characterized by pain, redness, swelling and sometimes loss of function.

conjunctivitis Inflammation of the inner membrane surrounding the eyeball, characterized by redness and often accompanied by a discharge.

tarantula Any of various large, hairy, chiefly tropical spiders of the family Theraphosidae and capable of inflicting a painful but not seriously venomous bite.