The Benefits Of Spiders
November 19, 2013
Do you know much about spiders? Many people think that spiders are insects but that’s not true. They can be distinguished easily from insects since spiders have two major body regions and four pair of legs while insects have three body regions and three pair of legs.
Spiders vary widely in color, shape, size, and habits. All produce venom that is poisonous to their normal prey but , fortunately, few spiders are considered dangerous to humans. These creatures are predators by nature. They use venom injected through hollow fangs or chelicerae to immobilize their prey. Spiders normally feed on insects and other small arthropods but there are some large tropical species that capture small mice, rats, birds, or even fish. Interestingly, spiders can only ingest liquids. Digestive fluids are either injected into the prey or regurgitated onto it and the spider drinks the liquified material.
Spiders are generally considered beneficial in spite of the number of people who shudder when they see them. This is for two main reasons: they consume large numbers of insects and are of almost no importance as disease carriers. It’s unfortunate that spiders do not differentiate between beneficial and destructive insects in their diet.
Spiders produce silk, which is secreted as a liquid through the spinnerets and hardens on contact with air. Many different types and textures of silk are produced by various species. The silk is used to construct snares or webs, egg sacs, drag-lines, and ballooning threads. Many spiders produce web snares of various designs to trap prey, and all construct a silk sac in which to deposit their eggs. Some egg sacs are quite elaborate, with four or more distinct types and many layers of silk, while others have only a few individual strands. Most species attach drag-lines of silk to the substrate at intervals wherever they go. This is why spiders always seem to have a silk thread to hang by if knocked from their perch. “Ballooning” is the term used to describe spiderlings sailing through the air on wind currents. These young spiders climb to a high point and release silk strands until the drag from the wind is sufficient to support their weight. Then, they release their hold and sail away, sometimes for considerable distances. It is these ballooning threads (sometimes called “gossamer”) that can fill the air on clear days as spiderlings disperse to new areas.
Spiders reproduce by laying eggs that hatch into spiderlings. For a spider to grow, it must shed or “molt” its rigid outer skin. The increase in size from one growth stage to the next occurs between the time the old skin is shed and the new one hardens. Most spiders live either one or two seasons, and molt from 4 to 12 times. Some tarantulas (not found in North Carolina) can live up to 20 years. Depending on the species, spiders over-winter as eggs, spiderlings in the egg sac, immature spiders living outside the egg sac, or as adults.
Common Non-Poisonous Spiders in North Carolina
Wolf Spiders: Wolf spiders are the largest spiders found in North Carolina. Their bodies are covered with short hairs in shades of brown, black, gray, white, yellow, or green. They stalk their prey rather than construct ing web snares. Female wolf spiders often have bodies up to 1 1/2 inches long. Some species seek shelter under leaves or debris while others construct retreats in shallow tunnels or dig deep burrows. Egg sacs of most wolf spiders are globular and are carried by the female attached to her spinnerets. Upon hatching, the spiderlings climb onto their mother’s back and ride there for several days before dispersing. Wolf spiders often alarm homeowners because of their large size and rapid movement. They are often a cause of concern to people in the late summer and fall when cooler temperatures prompt them to enter homes. In spite of this invasion, wolf spiders are not considered “house spiders” and generally do not become established in homes.
Garden Spiders: These spiders, sometimes referred to as argiopes, are the largest web-spinning spiders in North Carolina. Full-grown females of the common North Carolina species exceed one inch in body length; males are often much smaller. Argiopes construct beautiful, large “orb” webs in gardens and tall vegetation. One common species, the black and yellow garden spider, has silver hairs on the back of its forward body section and a large abdomen marked, in black and bright yellow. Their egg sacs are spherical, narrowed at one end, up to one inch long, and covered with a tough, brown, paper-like silk. Another common species, the banded garden spider, is similar to the previous species in its habitat, web construction, and size, but the abdomen is marked with alternating thin, broken, horizontal silver and yellow lines on a black background. Garden spiders often attract a great deal of attention due to their size, bright coloration, large orb web, and their habit of building webs in open areas near human habitations. Some people are uncomfortable working around such large spiders, but many gardeners welcome these attractive insect-eaters.
Crab Spiders: Crab spiders are well named. The body is compressed (top to bottom), short, and broad. The first two pair of legs are larger than the last two and are held in crab-like fashion away from and in front of the body. Crab spiders are able to walk backwards and sideways as well as forwards. Most North Carolina species are small with body lengths of less than 1/2 inch. They depend on good eyesight, speed, and camouflage to detect and catch their prey. Species that inhabit trees or hunt on the ground are usually colored in shades of gray, brown, or black. Those that frequent flowers are more often brightly colored in red, yellow, orange, white, and/or green. These spiders mimic the colors of the flowers upon which they rest to ambush their prey. Some species have the ability to alter their color to match the background. A few species commonly found on plants even mimic bird droppings.
Jumping Spiders: Jumping spiders are very common in North Carolina. They depend on their vision (the keenest of all spiders) and leaping ability (they can jump several times their own length) to capture their prey. Jumping spiders have a hairy, stocky appearance, hunt by day, and are common in sunny areas. North Carolina species are generally 1/2 inch long or less, and are gray, brown, or black with red, orange, or white markings. Jumping spiders stalk their prey with a slow, irregular gait, covering the final distance by springing into the air and landing on their prey. Just before jumping, the spider attaches a drag-line to the substrate and extends its front legs in preparation for seizing its intended victim.
Funnel-Web Spiders: “Funnel weavers” are the spiders responsible for the large, flat, sheet-like webs that occasionally cover certain shrubs, such as junipers and yews, in the fall. Webs are also constructed in lawns, window wells, and numerous other locations. At one end of the web is a funnel that leads to the spider’s retreat. The spider waits at this narrow end and detects insects by the vibrations made when the web is touched. The spider then runs out on the upper surface of the web, grabs the prey, and returns to the funnel to consume its meal. North Carolina species are nearly one inch long and are variously marked in shades of gray, brown, white, black, or dull yellow.