Spider Identification and Management by Gary L Jensen, Will Lanier and Catherine E. Seibert

Spider biology. How to identify house or comb-footed, orb weave, funnel web, aggressive house, recluse, wolf, jumping and crab or ambush spiders. MT199210 AG Reviewed 3/05

any people fear spiders at the posterior end, from which silk chelicerae, which have openings at more than household in for spider webs is spun. By contrast, all the tips connected to ducts leading Msects like ants, cockroaches, adult insects have three pairs of legs, from poison glands. While all spiders crickets, and other common arthropods. one pair of antennae, and three body have poison glands, only a few are This fear often is caused by a lack of regions: head, thorax and segmented poisonous to humans. When spiders information about or experience with abdomen which has no spinnerets. capture prey, their bite injects venom spiders. A report by television, radio Many adult insects have one or two and digestive fluids, paralyzing their or newspaper that a person has been pairs of wings. victim. While the prey is immobilized, bitten by a black widow or a brown All spiders are predators and will eat the spider sucks out the liquefied, recluse spider often triggers a flood of one another. A few will also scavenge. digested tissues, leaving only an empty queries. People call or submit samples They are numerous and probably play shell. Other spiders crush the body to county agents, health departments a useful role in keeping insects and of their prey, bathe the tissues with or extension specialists requesting other arthro-pods in check. Insects, on digestive fluid, suck up the digested information about these creatures. the other hand, feed on nearly anything liquid, and continue chewing and For example, in spite of all the organic: plants, animals, wood, rolling the body until only a little ball publicity it has been given, the brown garbage, stored products, etc. Some of indigestible material remains. insects are highly beneficial, others are recluse spider is not yet known to Spider identification inhabit Montana, yet bites by other pests, and others are neither. spiders are often misdiagnosed as About 50,000 species of spiders have brown recluse bites. And while Spider biology been described. While one person black widow spiders are common in Female spiders are usually larger than is not able to identify all spiders, Montana, much of the fear concerning males and have a pair of appendages county agents, health officials and them is not warranted despite their on the head called pedipalps that others can easily learn to identify unsavory reputation. resemble legs. After mating, female important spiders, just as people learn County agents and health officials spiders spin silken egg sacs in which to recognize poisonous snakes and can do a better job of dispelling they lay masses of eggs. After some poisonous plants. fears about spiders if they have some time, young spiderlings hatch and The only truly poisonous spiders knowledge about spider identification emerge from the egg sac. They grow in Montana are the black widow, a and biology. by periodically molting or shedding very docile, non–aggressive spider, old skin. Spiderlings molt from four (unless the female is protecting the Spiders contrasted to insects to twelve times before reaching the egg sac), and the aggressive house Spiders differ from insects in several adult stage. Young spiders resemble spider. Even though the brown recluse respects. They have four pairs of legs, adults, living and feeding in the same spider has not been found in Montana, no antennae, no wings, and only two environment. Spiders catch and feed county agents and others should be body regions. The head and thorax are on many kinds of insects and other familiar with certain distinguishing combined and called the cephalothorax. arthropods. characteristics so that they can quickly eliminate it when spiders are brought to The cephalothorax is attached by a Spider mouth parts are quite them for identification. Spider families narrow pedicel to an unsegmented different from insect mouth parts. are easily identified by the position abdomen. The abdomen has spinnerets They have a pair of pincers, called and number of eyes, the overall shape,

* Extension Integrated Pest Management Specialist (retired), Insect Diagnostician, and Herbarium Collection Manager and Ext. Plant Taxononist, Montana State University, respectively. All drawings by Catherine E. Seibert E-5 House spiders House spiders are among the most common spiders found in buildings. Two of their lateral eyes touch each other on each side of the cephalothorax and are well separated from the other four eyes. Female house spiders have bodies which are l/8 to 3/8 inches long and the abdomen is often covered with dirty whitish or brownish hairs arranged somewhat like chevrons. House spiders spin irregular sheet webs in protected Latrodectus hesperus places in the corners of rooms, ledges, Western Black Widow windows and under furniture. Unlike black widow spiders, males and females Steatoda sp., House Spider are often observed living together in the same webs. Webs of house spiders often Family Theridiidae have dead insects entangled in or lying “House or Comb-footed Spiders” beneath them. Latrodectus variolus Medium to small sized, glossy spiders with globular Some common household spiders, abdomens, thin legs bearing few spines, and eight relatively Northern Black Genus Steatoda, are in the same Widow large, protuberant eyes. House spiders, except for the “widows,” have two of the lateral eyes touching each other on family as the black widow, but are not each side and well separated from the other four. poisonous. Adult females resemble the black widow in size and shape; however, length of legs and form of the spinnerets. They are distinguishable by their color there is no red hourglass marking on the If a person is bitten by a spider and has markings. underside of the abdomen and there is reason to seek medical attention, it is The western black widow female’s often a whitish T-shaped marking on the important to have a specimen of the body is about half an inch long and the topside of the abdomen. suspect spider to aid in identification. male is less than half this size. Females Spiders around the home are found have a complete hourglass marking on Orb-weaver spiders around windows, screens and especially the underside of the abdomen, which is Orb-weaver or garden spiders are around outside lights, where insect prey usually completely black except for a generally large, with bodies l/2 to 1 are attracted. The first step in identifying small reddish spot near the tip. Males inch long. They often have conspicuous a spider is to determine if it is associated of the western black widow are usually black, white, yellowish or orange with a web. This MontGuide provides light brown whereas males of the other markings. These common spiders are a pictorial guide for determining some species of Latrodectus are generally often seen in late summer or fall. They important common species and families black. Males have three diagonal pale are able to construct large, conspicuous using conspicuous characteristics. stripes on each side of the abdomen. webs with a central hub from which The northern black widow spider spokes radiate. All this is constructed in Web spinning spiders is similar to the western black widow less than an hour. The female sits in the except the hourglass marking on the hub, waiting to detect movement that Black widow spiders underside of the abdomen is incomplete signals prey has been captured. After The black widow spider and its relatives or split into two triangles. The abdomen mating, the female seeks a protected in the genus Latrodectus are easily of the female is black with a row of place to lay a cluster of eggs, some 300 recognized by the hourglass marking reddish spots along the top and diagonal to 800, which will hatch the following on the underside of the abdomen. (See whitish bands on each side. Males have spring. illustration on this page.) This marking is four diagonal whitish bands on each side reddish or orange on live specimens, but of the abdomen. Funnel web spiders loses its color when preserved in alcohol. The bite of both the western and Funnel web spiders all have eight Black widow spiders get their name northern black widow is a neurotoxin eyes about the same size and slightly from the fact that the female frequently and is very painful. The pain occurs separated, bodies about l/2 inch long, eats the male after mating, a practice not less at the actual bite but rather in the and usually two dark longitudinal stripes uncommon to several other species of abdomen and limbs. Physiological on a grayish cephalothorax. The most spiders. effects are an accelerated heart beat, distinguishing characteristic is a long There are probably at least two increased blood pressure, breathing posterior pair of spinnerets. Funnel web species of black widow spiders in difficulties, and paralysis. When death spiders spin flat webs of silk which Montana—the northern black widow, occurs, it is due to suffocation. Although extend into tubes or funnels into which Latrodectus variolus, and the western the bite of a black widow is rarely fatal the spiders retreat for protection, hence black widow, Latro-dectus hesperus. it is important to seek medical attention. the name. The webs are often found Antidotes are commercially available. 2 Family Araneidae Agelenidae tegenaria-agrestis Family Loxoscelidae “Orb Weaver Spiders” “Aggressive House Spider” “Recluse Spiders” Legs rather stout and spiny. All eight Swift-running spider distinguished Distinctive violin-shaped marking eyes small, sub-equal, and seemingly from non-poisonous funnel web on the cephalothorax. The six grouped into pairs. Web is an orb spiders by chevron shape on its eyes are arranged in three pairs with a closed hub. Their retreat is abdomen and legs which are not forming a semicircle. often away from the web. banded like other funnel web spiders.

Redrawn from Levi and Levi, 1968

Redrawn from Katson, 1978 in shrubbery near buildings, or in the or threatened. The aggressive house Wolf spiders angles of windows, doors or buildings. spider is important medically because Wolf spiders are medium to large They reach the peak of their population of its ability to cause necrotic spider spiders, and are usually hairy, brown in late summer and fall and often enter bites. (A necrotic bite causes tissue to or black, with long legs adapted for buildings at that time. Most funnel- die.) The aggressive house spider is a running. They have good eyesight—an weavers die after the first frosts. Winter long–legged, swift running member of adaptation for chasing down their prey, is passed in the egg stage. the funnel web spider family. The brown paralyzing it and feeding. Webs are abdomen has a distinctive yellowish not used by wolf spiders. Female wolf Aggresive house spider chevron pattern. The legs are a uniform spiders carry the egg sac attached to their The aggressive house spider, Tegenaria brown without the darker brown bands spinnerets until the eggs hatch. They agrestis, is becoming one of the most that other nonpoisonous funnel web then carry the young spiderlings about common spiders in the Northwest. This spiders have. on their backs for a time. Some of the spider was first reported in the Seattle largest spiders encountered in Montana area in 1930. It is a prevalent spider Spiders that don’t spin webs are in this group. This group is very in basements and in window wells of mobile and may be found moving into houses. It rarely climbs vertical surfaces Brown recluse spiders houses in the fall in search of prey. and is usually found only on the ground Brown recluse spiders are easily or lower floors. Experts have called it the recognized by a combination of two aggressive house spider because it bites characteristics: a dark fiddle or violin- with little provocation when cornered shaped marking on the top side of the tan cephalothorax, and six eyes arranged in three pairs forming a semicircle. Most other spiders have eight eyes variously arranged. Adult female brown recluse spiders are about l/2 inch long (legs excluded); males are somewhat smaller. Both female and male brown recluse spiders can bite people and inject venom. Individuals react differently to bites. A stinging sensation is usually followed by intense pain. A small blister arises and a large swollen area around the bite Family Lycosidae becomes congested and swollen. While “Wolf Spiders” Family Agelenidae bites of the brown recluse are generally Eyes arranged in three rows with four “Funnel Web Spiders” not fatal, they result in a local necrotic large eyes on top and front of head and Spinnerets long, two segmented, and lesion that heals slowly, leaving an ugly anterior, slightly curved row of four small conspicuous. Eyes small, sub-equal, eyes. Females carry the globular egg sac and arranged in two relatively short scar. There are other spider bites that attached by the spinnerets. The fourth rows. Web is sheet or platform-like give a similar reaction, and these are pair of legs is the longest and frequently with a tubular retreat leading off from often misdiagnosed by well-meaning held stretched out behind the spider. the center or one edge. physicians as brown recluse spider bites. 3 Jumping spiders Family Salticidae Family Thomisidae Jumping spiders, like wolf spiders, “Jumping Spiders” “Crab or Ambush Spiders” do not spin webs to capture prey, but Square-fronted cephalothorax bearing First and second pair of legs distinctly rely on quickness and visual acuity. four very large anterior eyes. Legs longer and stouter than the third and usually short and stout with the first fourth. Abdomen usually broad at the Jumping spiders and wolf spiders have pair sometimes enlarged. Diurnal. posterior. Crab spiders are commonly two eyes much larger than the other seen on flowers, do not construct a six, probably an adaptation to help web, and are typically brightly colored. them better see their prey. Jumping spiders are small to medium sized spiders, usually stout bodied, short legged and hairy. They frequently have contrasting black, reddish, or yellowish markings. They are very agile, pouncing and feeding on small insects about the home. They are often seen on screens or near doors or windows. Crab spiders Crab or ambush spiders are somewhat crab-like in shape and walk sideways or backward. They are medium sized Management Bibliography and often brightly colored, with abdomens that are usually wide at Spiders are beneficial, preying on Akre, R. D. and Myhre E. A. 1991. the posterior end. The two front pair insects, so control measures should Biology and Medical Importance only be used in situations where they of the Aggressive House Spider, of legs are usually longer and stouter Tegenaria agrestis, in the Pacific than the two hind pair and crab spiders become intolerable—for instance, Northwest. Department of often hold their legs poised to trap where black widow or other spiders Entomology, Washington State insect prey. They have eight relatively pose a threat to individuals or pets. University, Pullman, WA. small, well spaced, light colored eyes. A broom or vacuum cleaner used to Kaston, B.J. 1978. How to Know the Crab spiders are usually found outside dislodge and move outside or crush Spiders, third ed. Wm C. Brown spiders will suffice. Keeping debris and Company Publishers. Dubuque, Iowa. in gardens and landscaping where 272 pp. wood piles away from living quarters they spin no webs but forage for their Jones, D. 1983. The Larousse Guide to prey or lie in ambush on blossoms or will aid in limiting food sources and Spiders. Larousse & Company, Inc. other parts of plants. They are able spider havens. Spiders are often found New York, N.Y. 320 pp. to gradually change colors to match outside under eaves and in corners of Levi, H.W. and L.R Levi 1968. A Guide flowers for camouflage. residences. By carefully manipulating a to Spiders and Their Kin. Golden broom, one can remove the spiders and Press. New York, N.Y. 160 pp. relocate them away from the house.

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The U.S. Department of Agriculture (USDA), Montana State University and the Montana State University Extension Service prohibit discrimination in all of their programs and activities on the basis of race, color, national origin, gender, File under: Insects and Pests religion, age, disability, political beliefs, sexual orientation, and marital and family status. Issued in furtherance of cooperative extension work in agriculture and E-5 (Household) home economics, acts of May 8 and June 30, 1914, in cooperation with the U.S. Reviewed March 2005 Department of Agriculture, Douglas L. Steele, Vice Provost and Director, Extension Service, Montana State University, Bozeman, MT 59717. (2000 03/05 GM)