Spiders can be divided into one of two groups, depending on how they capture their prey: web-builders and hunters.
All spiders produce silk, but hunting spiders do not construct webs to capture food. Instead, they chase down their prey and rely on their eyesight and quickness. Some of the more common hunting spiders include crab spiders (Thomisidae), jumping spiders (Salticidae), wolf spiders (Lycosidae), ground spiders (Gnaphosidae), and sac spiders (Clubionidae). These spiders often find their way indoors because of their food-seeking behavior. The brown recluse spider (Loxoscelidae), which is not often found outdoors in our area, is also a hunting spider.
In contrast, web-building spiders construct webs to help them capture their food. They either live in or near their web and wait for food to come to them. These spiders generally have poor eyesight, but have acute senses to feel vibrations in their web to detect prey. Some of the more common web-builders are the garden spiders, aka, orb weavers (Araneidae), funnel web or grass spiders (Agelenidae), and cellar spiders (Pholcidae). The black widow spider (Theridiidae) also is a web building spider, but is not often encountered in Nebraska, even though it is indigenous to this area. A common spider related to the black widow is the triangulated house spider, Steatoda triangulosa. Unlike the black widow, it is not a venomous spider.
Spiders are important predators in the landscape, feeding on many pest insects and are important in keeping the ecosystem in balance. The orb weavers are a large family and one of the more visible groups in late summer and early fall.
Orb Weavers. This is a large family of spiders, with more than 2,500 species in the U.S. This group gets its name from the distinctive wheel-like webs they spin. They are conspicuous spiders - often brightly colored - and can be small to large, ranging from 1/16 to 1-1/4-inches long. The males are often much smaller and less brightly colored than the females. Orb weavers have eight eyes arranged in a cluster of four in the center of the face. The lateral pair is often separated from the center four.
The females usually have a large, bulbous abdomen, but some species -for example, the Micrathena genus - may have conspicuous bumps (tubercules) or spines. The eight legs of orb weavers are usually spiny and are often banded.
Some of these spiders are extremely common. The garden spider - also known as the black and yellow argiope - is familiar to many people. Adult garden spiders are about one-inch long and black and yellow. Another familiar orb weaver is the barn spider. It is brown and is a bit smaller than the garden spider, about 4/5-inch long. The photo to the left was taken by Kate Brooke.
The Web. Orb weavers often anchor their web to sides of buildings and other man-made objects. They usually build a new web every night by recycling last night's web. Towards evening, the spider will eat the old web, rest for an hour or so, then spin a new web in the same general location. Most orb weavers spin spiraling sticky threads on (non-sticky) support lines that radiate outward from the center hub. The actual catching area is the sticky spiraling part of the web. As the spider waits for prey to get caught, it sits in the hub, which isn't sticky. Check out a very neat animation of this at "How Stuff Works."
When an insect blunders into the sticky lines of the web, the vibrations mobilize the orb weaver. The prey is stunned by a quick bite and wrapped in silk.
So, how do orb weavers keep from getting caught in their own webs? This has been one of nature's mysteries. Old theories suggest that spiders do not stick to their own webs because their bodies are oily, which keeps them from adhering to their web. A second theory is that spiders avoid stepping on the sticky parts of the web. But, this doesn't explain how the spider must cross the sticky part of the web to get to insects caught in it.
A recent study using modern imaging technology conducted by a two biologists in Costa Rica, Daniel Briceño and William Eberhard, may have solved this mystery. They noticed the spiders used the dry threads for traveling most of the time. But, when they went to retrieve prey caught in the sticky part of the web, the spiders walked very carefully, holding their body clear of the web, making minimal contact with the sticky threads with only the tips of their legs. They also discovered that the spiders' legs are protected by a covering of branching hairs and by a non-stick chemical coating.
Wolf Spiders. Unlike the orb weavers, wolf spiders are active hunters and do not build webs, although they may use silk for constructing a retreat to rest. As their name suggests, wolf spiders run on the ground in search of prey and pounce upon victims with vigor and power. They have good eyesight and an arrangement of eyes that distinguishes them from other groups of spiders. Two large prominent eyes are directed forward, four smaller eyes are under those, and two eyes are located further back. Among the spiders, only jumping spiders have better eyesight. The photo to the right was taken by Jim Kalisch, University of Nebraska.
Wolf spiders are found in most terrestrial habitats, but are common in areas of tall grass or shrubs where a plentiful insect supply is available. They are extremely common spiders, but alarm many, especially when the larger species are found indoors.
Some species of wolf spiders are quite large - as much as 1-1/2 inches in body length - but there are smaller species less than 1/4-inch. These spiders are feared and often described as "big, hairy, and real fast". Coloration is typically black to brown to gray with various markings or lines.
The female spins a large spherical egg sac, attaches it to her spinnerets and drags it around until the eggs hatch. After emerging, spiderlings cling to their mother's back and ride with her for about a week.
Wolf spider bites are not dangerous, though as with all spiders, bites may cause reactions in certain individuals. Spiders captured indoors in a container can be taken back outside and released.
Spider Management. Spiders are considered creepy and even dangerous creatures by some people. However, as a group, spiders are important predators in the landscape, playing an significant role in the outdoor ecosystem.
Prevention and Nonchemical Control
Spiders enter houses and other structures through cracks and other openings. To prevent spiders from coming indoors, seal cracks in the foundation and other parts of the structure and gaps around windows and doors. In addition, good screening will keep out insects that they must have for food.
Regularly vacuum corners of rooms, storage areas, basements, and garages to remove spiders and their webs. A web on which dust has gathered is an old web that is no longer being used by a spider.
In storage areas, place boxes off the floor and away from walls to prevent them from being a spider harborage. Seal boxes with tape to prevent spiders from crawling inside. Remove clutter in garages, sheds, basements, and other storage areas. Be sure to wear gloves when cleaning to avoid accidental bites.
Sticky traps offer a non-insecticidal way to remove spiders from your home, if placed in locations where pets and curious children can't tamper with them.
To discourage spiders outside near the foundation, keep that area free of trash, leaf litter, heavy vegetation, and other accumulations of materials. Trim plant growth away from the foundation. Outdoor lights attract insects, which, in turn, attract spiders. If possible, keep lighting fixtures off structures and away from windows and doorways. Use yellow light bulbs which are less attractive to insects. Sweep or vacuum webs and spiders off buildings regularly.
Numerous pyrethroid insecticides labeled for spider control are available in retail outlets. Active ingredients containing pyrethroids often have the suffix "thrin". These are contact insecticides, meaning if you spray a spider, it will be killed if the spray lands directly on it. Unfortunately, these sprays do not have a long-lasting residual effect.
Sorptive dusts containing silica aerogel or diatomaceous earth can be useful when applied in cracks and crevices, wall voids, and similar locations. When spiders crawl across a treated surface, the dust contacts the spider cuticle and abrades the waxy layer. Eventually, the spider loses moisture and dies.
Sources: Field Guide for the Management of Urban Spiders, Hedges and Lacey; How Stuff Works http://www.howstuffworks.com/; R.D. Briceño and W.G. Eberhard. 2012