Four desert arachnids, all spider relatives, create feelings of concern and even fear in the hearts and minds of those who come in contact with them. Two of them, the black widow spider and Arizona brown spider, are well deserving of respect. The other two are actually quite harmless; only their appearance gives them a hard reputation. Here are some answers to commonly asked questions about these interesting animals.
Black Widow Spiders. The adult black widow spider female is colored glossy-black with a bright orange to red hourglass-shaped marking on the underside of the abdomen. The body of the female is about ½ inch long and, with legs extended, may be up to 2 inches long. The males also have the red hourglass on the underside of their abdomen, but are cream and tan in color and much smaller in size. Newly hatched black widows are white with black spots on their abdomen with a cream-colored hourglass. Later, as they mature, they become cream and brown-striped. All stages of both sexes are venomous. Even the egg sacs contain poison, and should be carefully removed and crushed.
Black widow webs are irregularly shaped with strands running in many directions. The somewhat stiff webs are said to appear “messy”, meaning that they have no particular pattern. The spiders hide during the day, and hang upside down in their webs at night. When mature, the female mates and lays several hundred eggs. She then wraps the eggs in a silken cocoon called the “egg sac”. Female black widows guard the sac until the eggs hatch. During this time she is most likely to bite when threatened. Egg sacs are most frequently encountered from May to October.
Black widow spiders do not aggressively hunt humans, but will bite to defend themselves. Be cautious when picking up or moving objects, particularly in outbuildings such as sheds or garages, or in shady, undisturbed areas such as under parked cars or in flower pots. Although they are not commonly found indoors, it is always a good idea to shake out and check clothing before dressing.
Black widow venom is a nerve toxin, which means that as it acts on the nervous system, it causes progressive muscle pain and can sometimes cause difficulty in breathing. The initial bite has been described as anywhere between a pin prick and a sharp stabbing pain, but some people do not even realize that they have been bitten. Although bites are generally not fatal, they should be considered dangerous. Contact the local Poison Control Center immediately for information about treatment and care if someone is bitten.
Sun Spiders. Sun spiders may be up the three inches long, and are usually tan or light brown in color. Although they are not scorpions, sun spiders are sometimes called windscorpions because they can move very quickly. Scientists call them solpugids, which is based on their scientific name.
Although they may appear grotesque to someone who has never seen one before, they are relatively harmless. Sun spiders have the ability to bite, but it is more like a pinch and they have little or no venom. They do not have a stinger so they can not sting. In fact, sun spiders can be considered to be beneficial because they eat pest insects. Because sun spiders do not pose a health risk to humans, they do not require chemical control.
Sun spiders are common residents of hot, arid regions. Over one hundred species are found here in the Southwest. They hide under rocks and stones during the day and hunt for insects and other invertebrates at night. They often come to outdoor lights to feed on the insects the lights attract.
Occasionally sun spiders may enter homes where they might become a nuisance. Most can be captured, then removed to the outdoors and set free. Sun spiders which find their way inside and, for one reason or another must be killed, are easily dispatched with a vacuum cleaner or fly swatter. To discourage sun spiders from coming indoors, turn off outdoor lights as much as possible. Make sure screens and doors fit snugly, and fill or cover all cracks or holes in exterior walls and foundations.
Arizona Brown Spiders. Arizona brown spiders are often mistaken for the brown recluse spider, which is not a normal resident of Arizona. The only brown recluse spiders found here are the ones who have been brought into the state in luggage or belongings of persons who recently come from regions where it does occur. This hitch hiking, fortunately, does not happen frequently. However, because these spiders are so closely related and because the venom of each causes similar symptoms, they are often treated, and feared, as one in the same.
The two species of brown spiders in Arizona closely resembling the brown recluse spider have a dark brown marking on the front portion of their body which resembles a lyre or violin. They appear two-toned, with a tan front and gray rear body region. These spiders have three pairs of eyes in a crescent shape across the top, rather than the four pairs of most other spiders. Arizona brown spiders are small. Including legs, their total size is only about the area of a nickel. The body region of adults is one-third inch long.
Arizona brown spiders normally nest in protected areas, such as under wood or dead cacti in the desert, their native habitat. They can be found in urban areas, but it usually is because they have been brought in from the desert on firewood or pieces of cactus skeleton acquired for landscape purposes. They build a loose web of white silk where they stay during the daylight hours. As with the black widow, Arizona brown spiders are active at night.
Once again, these spiders are normally quite timid and only bite when trapped. Persons bitten apparently at first feel no discomfort, but as time progresses a blister forms, which may become an open ulcer. Other symptoms include fever and nausea. Persons bitten should make every attempt to capture the spider for identification and call the local Poison Control Center immediately.
Tarantulas. Tarantulas are the largest spider found in this region, up to six inches in diameter. They are hairy and are often black with red markings.
Despite their large size, tarantulas are not aggressive, and they rarely bite. If they are harassed into biting, the bite is not considered dangerous. There is little lasting pain or subsequent serious health problems. However, as with many other biting and stinging creatures, if an individual is allergic to the venom, they may have a more serious reaction and should seek medical attention immediately.
Believe it or not, the tarantulas’ hairs can be more harmful than their bite. When threatened, tarantulas stroke the back of their abdomen with their hind legs and “kick” off fine, barbed hairs. These hairs introduce a toxin into the skin that can cause burning and itching, and may result in a serious skin rash.
While it is true that some Arizona spiders are truly venomous, there are many more that either have no venom or are not a serious threat to humans. By being aware of which are and which are not a credible threat, we can learn to enjoy the desert creatures and protect ourselves as well.
If you have questions, you can reach one of our Master Gardener volunteers at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221, extension 204. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85122
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
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