Spiders Integrated Pest Management in and Around the Home and Landscape
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SpiderS Integrated Pest Management In and Around the Home and Landscape Many people fear or dislike spiders but, of the large, round abdomen (Fig. 2). for the most part, spiders are beneficial The body, excluding legs, is 5/16 to 5/8 because of their role as predators of inch long. Only the larger immature insects and other arthropods, and most female and adult female spiders are cannot harm people. Spiders that might able to bite through a person’s skin and injure people—for example, black inject enough venom to cause a painful widows—generally spend most of their reaction. time hidden under furniture or boxes, or in woodpiles, corners, or crevices. The adult male black widow is one-half The spiders commonly seen out in the to two-thirds the length of the female, (actual size of body 5/16 to 5/8 inch long) open during the day are unlikely to bite has a small abdomen, and is seldom people. noticed. The male black widow does possess venom, but its fangs are too Figure 1. Adult black widow spider. IDENTIFICATION small to break human skin. The top Spiders resemble insects and some- side of its abdomen is olive-greenish tough and paperlike on the surface. A times are confused with them, but they gray with a pattern of cream-colored female may produce several egg sacs. are arachnids, not insects. Spiders have areas and one light-colored band going Tiny, young black widows, which are eight legs and two body parts—a head lengthwise down the middle. The nearly white in color, disperse to new region (cephalothorax) and an abdo- hourglass mark on the underside of locations by ballooning and infest new men. They lack wings and antennae. the abdomen typically is yellow or yel- areas. Although spiders often are found on low-orange and broad waisted. The legs plants, they eat mainly insects, other are banded with alternating light and Where the Spiders Live. Black widow spiders, and related arthropods, not dark areas. Contrary to popular belief, spiders occur in most parts of Califor- the female black widow rarely eats plants. Most spiders have toxic venom, nia. They and their associated webs the male after mating but may do so if which they use to kill their prey. How- usually are found in dark, dry, shel- hungry. Like males, young female black ever, only those spiders whose venom tered, relatively undisturbed places widow spiders are patterned on the top typically causes a serious reaction in such as among piles of wood, rubbish, side. In the early stages they greatly humans are called “poisonous” spiders. or stones; in culverts, hollow stumps, resemble males but gradually acquire See the sidebar: Spider Bites. Common and old animal burrows; in garages, the typical female coloration with each spider families are described in Table 1. sheds, barns, crawl spaces, utility meter shedding of the skin. In intermediate boxes, and outhouses; and sometimes stages they have tan or cream-colored, among plants. People are most likely to Black Widow Spider olive-gray, and orange markings on the The black widow spider, Latrodectus be bitten when they disturb the spider top side of the abdomen, a yellowish hesperus while they are cleaning out or pick- (Fig. 1), is the most common orange hourglass mark on the under- ing up items in such places. A sensible harmful spider in California. Venom side, and banded legs. from its bite can cause reactions rang- precaution is to always wear gloves and a long-sleeved shirt when working in ing from mild to painful and serious, Webs and Egg Sacs. The web of the but death is very unlikely and many black widow is an irregular, tough- symptoms can be alleviated if medical stranded, sticky cobweb mesh in which treatment is obtained. Anyone bitten the spider hangs with its underside up. by this spider should remain calm and During the day it often hides under an promptly seek medical advice; it is object at the edge of the web or stays in helpful if the offending spider can be a silken retreat in the center. The black caught and saved for identification. widow may rush out of its hiding place when the web is disturbed, especially The typical adult female black widow if egg sacs are present. The egg sacs are has a shiny black body, slender black mostly spherical, about 1/2 inch long legs, and a red or orange mark in the and 5/8 inch in diameter, creamy yel- Figure 2. Two variations of hourglass shape of an hourglass on the underside low to light tan in color, opaque, and markings of black widow spider. EST OTES Publication 7442 PUniversity of California N Agriculture and Natural Resources Revised November 2007 November 2007 Spiders Spider Bites areas that have been undisturbed for a Unlike mosquitoes, spiders do time and where there are good hiding not seek people in order to bite them. places for spiders. Generally, a spider doesn’t try to bite a person unless it has been squeezed, Effects of the Bite. The symptoms of a lain on, or similarly provoked to defend black widow bite are largely internal; itself. Moreover, the jaws of most spiders little more than local redness and are so small that the fangs cannot swelling may develop at the bite site. penetrate the skin of an adult person. (actual size Sometimes when a spider is disturbed in The internal effects may range from of body ~ 5/8 inch) its web, it may bite instinctively because mild to severe. Pain tends to spread it mistakenly senses that an insect has from the bite to other parts of the body Figure 3. Adult yellow sac spider. been caught. and muscular spasms may develop. In The severity of a spider bite depends severe cases the abdominal muscles on factors such as the kind of spider, may become quite rigid. Other effects the amount of venom injected, and the age and health of the person bitten. A can include profuse sweating, fever, spider bite might cause no reaction at increased blood pressure, difficulty all, or it might result in varying amounts breathing and speaking, restlessness, of itching, redness, stiffness, swelling, and nausea. Typically, the pain and and pain—at worst, usually no more other symptoms reach a maximum severe than a bee sting. Typically the within a day of the bite, then gradu- symptoms persist from a few minutes ally subside over the next 2 to 3 days. to a few hours. Like reactions to bee stings, however, people vary in their Most people who are bitten spend a few Figure 4. Head region of recluse spider responses to spider bites, so if the bite of hours under observation by a physician (left) and yellow sac spider (right). Note the arrangements of the eyes: the recluse any spider causes an unusual or severe but do not develop symptoms severe spider has six eyes arranged in three reaction, such as increasing pain or enough to require treatment. Small pairs and the yellow sac spider has eight extreme swelling, contact a physician, children, the elderly, and persons with eyes arranged in two rows of four. hospital, or poison control center (in health problems are likely to suffer California, the number is 1-800-222- some of the more severe consequences 1222). Recluse Spiders Sometimes a person may not be of the bite. Black widow bites are fairly Recluse spiders of the genus Loxosceles aware of having been bitten until pain common in California. include the well-known brown recluse and other symptoms begin to develop. spider, L. reclusa, which does not Other species of arthropods whose bites Yellow Sac Spider occur in California. While the brown or stings may be mistaken for that of a The common, house-dwelling agrarian recluse has occasionally been brought spider include ticks, fleas, bees, wasps, sac or yellow sac spider, Cheiracanthium into California in household furnish- bedbugs, mosquitoes, the conenose inclusum, is a small spider that spins ings, firewood, and motor vehicles, it (kissing) bug (Triatoma protracta), does not reside in the state. However, deer flies, horse flies, and water bugs a silken sac web in the corners of ceil- populations of another recluse spider, (Lethocerus spp.). ings and walls, and behind shelves and the Chilean recluse spider (L. laeta), For first aid treatment of a spider pictures; it is also commonly found out- bite, wash the bite, apply an antiseptic doors in shrubbery. This spider is light were found in Los Angeles County in the late 1960s. In its native Chile it is to prevent infection, and use ice or yellow and has a slightly darker stripe known to have a bite that is toxic to ice water to reduce swelling and on the upper middle of the abdomen discomfort. Bites or stings from a humans. The native recluse spider of (Fig 3). The eight eyes of this spider are variety of arthropods can result in an California (L. deserta) is found in the all about equal in size and arranged in itching wound. Rather than scratching, desert regions of southern California if necessary, try to relieve the itch with two horizontal rows (Fig. 4). and neighboring states. Its bite can medication. Scratching can break the cause problems, but it is not as toxic as skin and introduce bacterial infection, Yellow sac spiders can be seen run- that of the Chilean recluse. In any case, which you or even a physician may ning on walls and ceilings at night and bites from the desert recluse are rare mistake for an arachnid bite.