What members of this subphylum pose the most serious health threat in Arizona?

Recognized by the eight legs attached to the cephalothorax, spiders are very useful and should not be killed. They eat only insects and other small pests and deserve a better reputation than they have. While all spiders kill their prey by injecting poison, only two spiders in Arizona have the ability to actually harm most people.

The Black Widow, Latrodectus mactans, and the Brown Recluse, Loxosceles reclusa produce dangerous bites. Both these spiders hunt at night and prefer out of the way places to hide during the day. Most are encountered when people reach into small, protected places. A favorite habitat for both of these spiders is a wood pile or brush pile. The Black Widow is more common than the Brown Recluse in Arizona. Neither is overly aggressive and only bite when they feel threatened.

It has been reported that the venom of the black widow spider is 15 times as toxic as the prairie rattlesnake. Whether that is true or not, always remember this about venomous bites. The severity of the bite depends on the amount of venom injected , the distance the bite is from vital organs, and the sensitivity of the person to the toxin. Obviously, a spider would inject a lot less venom than a rattlesnake.

The largest Arizona spider, the tarantula, is not considered harmful. The bite of this mild-tempered spider is no worse than a bee sting.

These insect-eating spiders might be seen around our school.
House spider	Wolf spider	Jumping spider	Crab spider	Garden spider

Another Arachnid in Arizona is the scorpion.

While the "sting" of a scorpion is more painful than most spider bites, scorpions are also predators of pests and should be protected. Scorpions catch prey with their enlarged pedipalps and tear their prey apart. The stinger on the tail is used mostly in defense.

While not venomous animals, ticks are a more serious threat to health than spiders and scorpions in Arizona. The American dog tick, Dermacentor variabilis, is a carrier of spotted fever and the black-legged tick, Ixodes scapularis, is the carrier of Lyme disease. While these diseases are not epidemic in Arizona, they are a threat that should not be overlooked.

	While both sexes take blood, it is the female (left) that engorges herself (right), after mating, to aid in egg formation. The male (center) takes a shorter blood meal, before mating, and will release itself when finished.
When removing embeded ticks, two things should be remembered: Pull the tick straight out, do not twist. There is a risk of tearing mouth parts off when twisting. Leaving parts of the tick in the skin can lead to serious infection. Body fluids from the tick can cause infection. Make every effort to protect yourself from these fluids when removing the tick.

Chiggers are actually the immature form of a mite. They do not bite, but secrete digestive enzymes into a hair follicle or skin pore and suck up the liquified cells. This is the process that causes the intense itching associated with chiggers. Scratching the area often leads to secondary infections.

You can see from the picture here that the larva has only six legs. After the meal from their host they will drop off and molt, becoming the adult mite with eight legs.

Research Links:

• Brown Recluse Spider - Virginia Cooperative Extension
• Common Household Pests - Urban Pest Control Research Center