Home and Garden AGRICULTURAL MU Guide PUBLISHED BY MU EXTENSION, UNIVERSITY OF MISSOURI-COLUMBIA muextension.missouri.edu Spiders Richard M. Houseman Department of Entomology Spiders belong to the order Araneae of the class Arachnida. They are most closely related to scorpions, ticks and mites. Spiders have a body composed of two regions called the cephalothorax (head) and abdomen Pedipalps (body). They have eight legs, no antennae or wings, and an unsegmented abdomen. Four, six or eight eyes are located at the front of the cephalothorax. Also located Eyes Abdomen at the front of the cephalothorax are the pedipalps, appendages used for handling food (see Figure 1). Spinnerets are located on the posterior tip of the Cephalothorax abdomen. These structures are used to produce silk. Silk is used by spiders to make webs, construct egg sacs, line Figure 1. Characteristic form and structure of spiders. nests, wrap captured prey, or construct “balloons” with which to travel on air currents over large distances. regulating insect and other arthropod populations in More than 300 different spiders occur in Missouri. many different ecosystems. Spiders have a pair of Some of the more common groups include orb weavers, hollow, fanglike mouthparts and venom-producing crab spiders, jumping spiders and wolf spiders. These glands that they use to subdue their prey. They pierce groups are distinguished by the size and shape of their the exoskeleton and inject venom through their fangs bodies, the structure of the legs and other appendages, like a hypodermic needle. The venom typically para- and the size and relative position of the eyes. Tarantulas lyzes their prey. They also inject digestive juices that are not very abundant in Missouri but are occasionally break down the internal tissues. Later, they use their collected from the southern part of the state. The brown mouth like a drinking straw to suck out the body fluids. recluse spider and black widow spider are the only two Not all spiders catch their prey in the same way. spiders in Missouri that are considered to be serious Some sit and wait on a web, while others leave their threats to human health. Most other species are consid- webs and actively stalk prey. Most spiders are active at ered nuisance pests when found in and around homes. night and usually remain hidden during the day. They Daddy longlegs will quickly run away when disturbed, unless they are (Figure 2) are not guarding an egg sac or young spiderlings. spiders but resem- Within a week after mating, females deposit eggs in ble them in shape a silken egg sac. The number of eggs deposited and the and number of number of egg sacs produced by a single female vary legs. They have according to species. It takes from a few weeks to a year segmented for the eggs to hatch and the young spiderlings to abdomens and Figure 2. Daddy longlegs. emerge. Young spiders typically climb to a high point only two eyes in their surroundings with suitable air currents, spin silk and do not produce silk. They are rarely found in the threads into the air and float away like tiny parachutists. living areas of a home. This behavior is called ballooning and aids in dispersal. Spiders generally live for only one or two years, but Spider biology and habits a few species can live as long as 5 to 20 years. Spiders All spiders are predators and should be considered grow by molting. This process consists of producing a beneficial in this role. They play an important role in new exoskeleton beneath the old one, splitting the old $.50 G 7386 Printed on recycled paper exoskeleton and climbing out, enlarging the body, and during courtship and mating. hardening the new exoskeleton. The molting process Unlike most spiders, jumping spiders forage for occurs repeatedly throughout the immature stages, but prey during the day. Since they are active during the day, after reaching maturity, the vast majority of adult they are often noticed by humans. They do not use silk spiders do not molt. It is not unusual to see accumula- to make a web for capturing prey. Instead, they stalk tions of shed exoskeletons in undisturbed areas of their prey by approaching slowly to a short distance homes with large spider populations. before making a sudden leap onto it. They use silk as an anchor, attaching a strand before leaping. This allows Wolf spiders (Lycosidae) them to climb back to their original location if they miss There are many species of wolf spiders and they are the prey. widely distributed and common. They vary in size from medium to large, some species Crab spiders (Thomisidae) measuring 2 to 3 inches in Crab spiders are distinctive in body shape (Figure diameter. Wolf spiders have 5). All of the legs extend sideways from the cephalotho- long, stout legs — the rax. The first two pairs fourth pair being the of legs are larger longest (Figure 3). The last than the last two, two pairs of legs have longer which gives hairs than the first two pairs. them a crablike Wolf spiders are found appearance. in a variety of habitats, They move about usually near moist by walking side- areas such as leaf litter, low- ways or backwards. growing vegetation, the Crab spiders do not edges of streams, ponds spin webs but capture Figure 3. Wolf spider. or rivers, and on sand- their prey by ambush. bars. They are known to Several species are brightly Figure 5. Crab spider. dig burrows or tunnel into natural cavities under colored and wait for their prey on objects. They actively stalk their prey during the night, flowers. They are known to catch a variety of flies and preying on ground-dwelling insects and other spiders. bees that come to flowers collecting pollen. Wolf spiders are known for their wandering habits, and it is not unusual to find some that have wandered Orb weavers (Araneidae) indoors. Orb weavers are often brightly colored with Female wolf spiders spin an egg sac attached to rounded abdomens, some with peculiarly angled their spinnerets. They are more aggressive when carry- humps or spines. However, there is considerable vari- ing an egg sac. When wolf spiderlings hatch, they crawl ation in size, color and shape in this group. They are onto the mother’s back and she carries them around for often recognized for building beauti- a short period of time. The young of most wolf spiders ful, large, round webs, on which pass the winter half-grown and finish development they rest, head downward, wait- during the following summer. ing for prey. The webs consist of a number of radiating threads crossed Jumping spiders (Salticidae) by two spirals. The inner spiral Jumping spiders vary from begins in the center, winds outward, small to medium-sized with and is made of smooth threads like the stout bodies and short legs radiating threads. It covers only the 1 (Figure 4). The cephalothorax central ⁄3 of the web. The outer and abdomen are nearly spiral begins at the edges and equal in size. The body winds inward. It is made of is usually very hairy and more elastic, sticky threads, coated is often iridescent or brightly with a liquid substance. colored. They usually live in One of the largest and most the tops of low-growing commonly encountered members plants. Males often have of this group is Argiope aurantia, the Figure 6. Orb weaver. peculiar bunches of hairs or yellow garden spider (Figure 6). It may cover an area spots on their legs and head, 1.5–2.0 inches in diameter when at rest. The cephalotho- and they use these features to rax is silver and the oval abdomen has a yellow and attract the attention of females Figure 4. Jumping spider. black pattern. The legs are mostly black, blending to tan Page 2 G 7386 at the bases. The web contains a large zigzag band radi- food. During the day they are resting in secluded places. ating out from the center. This spider feeds primarily on Other encounters occur when seldom-used clothes, grasshoppers and katydids. containing a spider that has been using the garment as a hiding place, are worn. Brown recluse spiders cannot Tarantula (Dugesiella hentzi) bite humans without some form of counterpressure. In Missouri, tarantulas are found only in the south- This pressure usually occurs when they are trapped ern part of the state. This large, hairy species is against the skin. uniformly choco- Both male and female brown recluse spiders are late brown with venomous. Human reactions to a brown recluse bite no noticeable vary considerably and depend on the amount of venom markings injected by the spider and the victim’s sensitivity to the (Figure 7). venom. A painful reaction can occur almost immedi- Tarantulas prefer ately, but often the victim won’t realize they have been drier areas, where bitten for an hour or more. Victims usually describe a they inhabit natural Figure 7. Tarantula. stinging sensation followed by intense pain. A small cavities or aban- white blister usually develops at the site of the bite. The doned burrows of other animals. They stalk crickets and affected area swells and becomes hard to the touch. This other large insects at night. The structure of their mouth- tissue dies and eventually sloughs away, leaving a parts is unique among spiders and requires them to sunken, ulcerated sore of various sizes. The typical reac- elevate their heads to insert their fanglike mouthparts tion has been described by physicians as unremarkable into prey. or mild and covers an area less than the size of a dime.