Spiders Spiders Class: Arachnida (Spiders, Daddy- Longlegs, Ticks, Mites, and Krista D
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Cooperative Extension Service College of Agriculture B-1050.5 February, 1998 Spiders Spiders Class: Arachnida (spiders, daddy- longlegs, ticks, mites, and Krista D. Davis, Jay D. Donahue and Michael J. Brewer1 scorpions Order: Many spiders can be found indoors in basements, crawl spaces, and other Araneida (spiders) areas where it is somewhat damp. Other species prefer a drier location Development: Simple (egg-immature-adult) and can be found in the upper corners of rooms, in attics, and in floor Mouthparts: vents. The presence of spiders in homes may be considered a nuisance Venomous piercing jaws due to some species’ habit of building webs in corners, closets, on furni- (chelicerae) ture, across windows, and around doorways. Some fear of spiders persists because of the myths of dangerous spiders and the publicity given to occasional hu- man poisonings from the bite of a few species. As a general rule, spiders are sel- dom aggressive toward humans and will usually only bite when trapped or injured. They naturally prey on insects and should be considered beneficial. General Body Form and Behavior of Spiders Egg: Females lay their eggs in dark, well-protected areas, or in silk cocoons called egg sacs. The females of some spe- cies guard their eggs, while other species carry the egg sac with them as they travel from place to place in search of food. Many common species of spiders produce Figure 1. Wolf spider. about 100 eggs per female. The eggs are usually laid over a period of time. Mating and egg-laying may occur at any time during the year, depending on the species of spider. Immature: Newly emerged spiders, known as spiderlings, scatter as quickly as possible after leaving their eggs. Spiderlings often disperse by a technique known as “ballooning.” The young spider sends out a silken thread which is picked up by the wind, carrying it through the air. This 1Former student, research associate and associate professor/specialist, respectively, Ento- mology Program, University of Wyoming method is used by most spiders and is ex- the abdomen. Some make webs and oth- tremely effective in transporting young ers do not. spiders. Spiderlings feed and develop over Life History and Body Form of a period of several months, during which Specific Spiders time they go through a number of molts, until the final molt to the adult stage. Spiders can be separated into two groups Most common spiders have one genera- based upon the way in which they cap- tion per year, with the adults appearing in ture their prey. The two groups are the the late summer months. “hunters” and the “waiters.” Spiders in the hunter group actively search for their Adult: Adults look like the immature in prey, and they may travel long distances body form and often in coloration and to find an area with sufficient food to markings. Spiders are members of the survive and reproduce. The waiters create Class Arachnida. Unlike insects, arach- a web and wait for their prey to get nids have only two body regions: a com- caught on the sticky silk. A brief overview bined head and thorax (or cephalothorax) of the life histories of some common spi- and an abdomen. Spiders have up to ders, categorized into each of the two eight simple eyes; insects generally have groups, is discussed below. two compound eyes. Spiders have four pairs of legs and no antennae. Like all Common hunting spiders are wolf spi- arachnids, spiders have knife–like mouth- ders (Lycosidae) and jumping spiders parts which pierce the bodies of their (Salticidae). prey. Both immature and adult spiders Wolf spiders are common, fast and large, inject a enzyme-containing venom into so they are often feared. Many of the spe- the prey. After the tissues have been thor- cies are approximately 1/2 inch in length, oughly digested inside the prey’s body, but some species reach a size of 1 to 1 1/2 the spider ingests the liquid through its inches. Most wolf spiders are brown or mouthparts. Spiders have silk-producing gray and move very quickly. They may organs, or spinnerets, on the underside of hunt day or night and do not produce webs. As the outside temperature drops, wolf spiders begin to move into sheltered areas, including homes, in order to escape the cold. During the summer wolf spiders may follow prey into buildings, but they are considered “outdoor” spiders. The larger species of wolf spiders can produce a mildly painful bite, but the symptoms do not last long unless secondarily in- fected. They have eight dark eyes which are unequal in size and are arranged in three rows of four, two, and two eyes from the front of the head to the top. Figure 2. Jumping spider. Jumping spiders are extremely active. Their bodies are robust and are often cov- ered with brightly colored hairs. They are most active during the day and jump while in pursuit of prey and when dis- turbed. The middle two eyes in the first (headmost) row are large and are seen easily. Most jumping spiders are between 1/8 to 1/2 inch in length. They seldom reproduce in homes, and human contact with them usually occurs during the late part of the season when they accidentally enter homes to survive the frosts. Figure 3. Orb weaver spiders. Common waiting spiders are orb weavers are commonly found in homes and are (Araneidae), funnel weavers (Agelenidae), often mistaken for wolf spiders or brown and cobweb spiders (Theridiidae). recluse spiders, most of them are not ag- Orb weaver spiders create large flat webs gressive and pose little threat to humans. which are made of threads radiating from However, one species of funnel weaver a central point with a circular design, and spiders has the potential for causing in- they wrap their prey completely in silk. jury—the hobo spider, also called the They tend to make their webs in tree aggressive house spider. This species has branches and corners of eaves, and attract been detected recently in western Wyo- attention because of their size and elabo- ming and is described below, in “Spiders rate web construction. Removal of webs of Special Concern.” is an effective way to reduce orb weavers Cobweb spiders (or combfooted spiders) and to detect new invaders. Orb weavers are extremely common in homes, and are attracted to buildings to make their most of the species in this group are ca- webs, but rarely enter homes. They vary pable of surviving indoors if there is an considerably in body shape but certain adequate food source (i.e., a large number species of this group may be the size of a of insects) available. These spiders range quarter in diameter as adults. from 1/8 to 1/2 inch in length and are Funnel weavers (or funnel-web spiders) generally found in irregular webs in dark vary in size from 1/8 to 3/4 inch, with areas such as the corners of rooms. Their dark-colored rings on their legs. They webs are often made with their bases at- produce funnel-shaped webs which are tached to the ground, sometimes with a made in lawns or in protected corners of tentlike mass of thread in which the spi- buildings during the late summer. Funnel der stays when inactive. Almost all cob- weavers may also be found in cellars and web spiders are completely harmless, ex- bathrooms and are often trapped in sinks cept for widow spiders. or bathtubs. Although funnel-web spiders Spiders of Special Concern Due though this pattern may vary, sometimes to Their Venom occurring as two unconnected dots. A few related species have similar markings Three species in Wyoming of special pub- but are less venomous. The webs made by lic concern are the black widow spider, widow spiders are large and irregular and the brown recluse spider (also known as are usually found in dark, quiet areas such the “fiddler,” “fiddleback,” or “violin” as abandoned rodent holes, shrubs, and spider), and the aggressive house spider. the corners of outbuildings. Widow spi- The venom of these species is highly ders also nest in crawl spaces and undis- toxic to humans. As with many other turbed parts of homes. health concerns, the very young, old, and ill members of the community may be Widow spiders tend to avoid trouble, but particularly susceptible to injury from become more aggressive when guarding bites made by these spiders eggs. Most bites occur when a person traps the spider against the skin uninten- These spiders all tend to avoid contact tionally. The bite of a black widow di- with humans whenever possible, but will rectly affects the nervous system, and a bite when threatened, disturbed, or when person who has been bitten by a female the female of the species is protecting an black widow will likely experience a egg sac. burning sensation, swelling, and redness Black widow spiders are widespread in in the area. Pain from a black widow spi- Wyoming. Full-grown female black der bite may become increasingly more widow spiders, the poisonous individuals uncomfortable and medical attention of this species, are approximately 1/2 should be sought. Severe cramping of the inch in length, are shiny black or dark leg, arm, and chest muscles is common, brown, and have large round abdomens. and in many cases, the abdominal Black widow females have reddish-orange muscles may also react in a similar man- markings on the underside of the abdo- ner. Black widow bites should be treated men in the shape of an hourglass, al- as soon as possible by trained medical personnel.