Wed, Nov 15, 2006 (7:09 a.m.)

You will likely notice a sharp pain, numbness or tingling at the site. Often, those will be the only symptoms and will pass in a few hours to a day. For questions, call the national Poison Center hotline at (800) 222-1222. If you lose control of muscles, have trouble with your vision or have difficulty breathing, go to an urgent care center or emergency room immediately, or call 911.

It's 2 inches of mean, and it's likely to be living in your back yard: bark scorpions, which are following people into Southern Nevada.

The bark scorpion isn't a pleasant neighbor. Like most Nevadans, it probably came from out of state, possibly piggybacking on palm trees, construction supplies and other materials from its native habitat in Arizona's Sonoran Desert. Over the last two decades or so, the scorpion has colonized Las Vegas, riding on the heels of urban growth.

"It has over the years spread quite a bit," says Jeff Knight, Nevada state entomologist. "It's moved out past the original introduction. Now it's pretty much spread all over Las Vegas."

He says bark scorpions, whose sting can be life-threatening, especially for children and older people, first showed up in Southern Nevada about 1990. The animals, which are arachnids - more closely related to spiders than insects - are found in the trunks or bases of palm trees and in crevices of cinder block walls. They are more active in the warm months and may move indoors in the winter, Knight says.

"I've had them turned in for identification every day of the year," he adds.

Bark scorpions are the newest members of a suite of stinging and biting critters found in the hot Mojave Desert. Gila monsters, rattlesnakes and several species of spiders - particularly the very common black widow - can be found in Southern Nevada. There are also scorpions native to Southern Nevada, including the giant hairy desert scorpion, which can grow up to 6 inches long.

Eran Gefen, a scientist doing post-doctoral research at UNLV, said there may be 10 or more species of scorpions living in Southern Nevada - and maybe some that haven't been identified yet.

Gefen is researching how scorpions interact with the dry desert environment. Although all the animals live in warmer parts of the world, some live in humid areas, others in the desert.

Most species, like the giant hairy desert scorpion, dig burrows. The sting of most scorpions, especially those around Southern Nevada, is relatively harmless except to those with allergic sensitivity.

The bark scorpion is an exception to both rules, Gefen says.

"It's pretty much the only deadly species in the U.S.," says Gefen, who received his doctoral degree at Tel Aviv University in Israel before coming to Nevada to conduct more research.

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State and county health officers don't track scorpion stingings, but local physicians say the numbers are rising.

Tom Higgins, an emergency room doctor at University Medical Center, has seen more than a few stings from the bark scorpion. Higgins, who is trained to handle venomous stings as an emergency toxicologist, worked in the Phoenix area, where the bark scorpion is relatively common.

"They are rapidly becoming all over the place here, too They are prevalent, they are small so they can get into quite small areas, and they can actually climb."

In fact, they can climb right into a bed.

The worst reactions to a scorpion sting can land the victim in the hospital. Higgins treated one person earlier this year who was initially diagnosed by emergency room personnel as suffering from cocaine intoxication. Higgins had to insert a tube into the patient's trachea to keep him breathing.

Such extreme reactions are unusual. Most stings do just that - sting - and don't have any serious complications.

Jim Christensen, a Las Vegas allergist, says he sees cases all the time. His wife and daughter have both been stung.

"Now that it's getting cool, these guys are looking for a nice warm place to spend the winter - like the attic of your house," Christensen says.

He warns that the "size of the scorpion doesn't correlate with its venom. The really small ones are the ones that give a lot of problems."

Ridding the house of bugs eliminates the food source for the scorpion, which Christensen called "a perfect predator." Indeed, the bark scorpion is especially good at controlling other insects, including cockroaches.

Outdoors, they hide around rocks and vegetation, he says. Christensen advises people who leave shoes outside to make sure they are empty before putting them on, and to wear gloves while landscaping.

Scorpions are unusual because they fluoresce, or light up, under black lights. Such lights are available at many department stores and will light them up, indoors or out.

There is "no getting rid of them," he says. "You've just got to be careful."

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