>> Monday, January 31, 2011

Spiders are beneficial inhabitants of any garden, ecosystem, or home because of their important contributions to biological control of pest insects. Spiders are considered to be the most important terrestrial predators, eating tons of pest insects or other small arthropods every year.  Spiders are generalist predators that are willing to eat almost any insect they can catch.

They can rapidly colonize a suitable habitat and they will eat enormous numbers of insects.  Since many spiders over winter as adults, they can reduce prey numbers early in the season before other biocontrol agents are active.

Garden spiders include the following: meshweb spiders, crab spiders, running crab spiders, wolf spiders, nursery web spiders, comb-footed spiders, stretch spiders, orb-web spiders, sheet web spiders, dwarf spiders, sac spiders, and buzzing spiders. Most all of garden spiders are orb weaving, which basically means that they are known for their orb looking webs.

There are many different types of garden spiders, as listed above, however two common species are the European garden spider and the Argiope garden spider. The European garden spider is recognized by its large tan and gray body with mottled tan or brown markings across the back, which is also highlighted by five or more large white dots forming a cross like shape. The Argiope, shown at right, usually is yellow or black with two rows of three white spots along its back. The Argiope also spins their web with a very unusual zigzag pattern in the center of it.

One of the most abundant spiders in the U.S. is the Wolf Spider, of the genus Lycosa. Its body (excluding legs) is about 0.6 of an inch long. In the drawing at the right the red circles are the eight eyes,  the pink ovals are the jaws (known technically as chelicerae) and at the very bottom of the two jaws you can barely make out two sharp, horizontal items, and these are the fangs.

Spiders are arachnids, not insects. They have two body segments instead of three, eight legs instead of six, and no antennae or wings. Unlike insects, spiders possess special body parts, called spinnerets, that allow them to spin webs.

All spiders are predators. They immobilize their prey with venom injected through specially designed fangs. The vast majority of the roughly 3,000 species that inhabit North America, however, are completely harmless to people. In fact, most species lack mouthparts that can penetrate human skin. Of those that can, there are only three that pose any threat to people: the black widow, the brown recluse, and the hobo.

The stereotypical spider spins a web in the vegetation and waits patiently for an insect to stumble or fly into the sticky threads and become trapped. Many of the most commonly seen spiders use this method. Other species don’t use webs at all to capture their prey. Wolf spiders, for example, stalk and actively hunt for their food on the ground. Jumping spiders also stalk their prey and, as their name suggests, capture food with impressive pounces many times their body length. Other spiders, such as crab spiders, lie waiting in camouflage for an unsuspecting insect to come within striking range. Some spider species even inhabit tunnels or funnel-shaped webs from which they snatch prey.

One thing is true of all spiders: They’re phenomenal predators of a vast array of insect pests. Collectively, spiders consume everything from aphids and beetles to moths and mosquitoes. Anyone with a garden—indeed, anyone who spends any time outdoors—should welcome spiders. Use these tactics to attract spiders to your garden:

  • Eliminate pesticides. Chemical sprays temporarily eliminate pests, but many also kill pest predators such as spiders. It’s much more sustainable and healthy to practice organic gardening and rely on natural pest predators.
  • Provide a diversity of plants. They attract many more spiders than a lawn alone.
  • Build a brush pile or rock wall.  They make excellent hunting grounds for spiders. If you live in an area with venomous spiders, wear gloves when moving brush or rocks, and you’ll be safe from accidental bites.
  • Leave part of your yard a little overgrown. Spiders over winter as adults inside or under dead vegetation, or as egg cases. They help ensure a healthy spider population next spring, ready to gobble unsuspecting garden pests.

It is very true that most spiders cannot even penetrate through our skin, even though most mystery bites are wrongfully blamed on spiders.

Spiders eat about 80% of bugs eaten by predators, more than ladybugs or mantis and they are indiscriminate feeders as long as the size is right, so can help you in many more places than other invertebrate predators!

To give you a sense of proportion, out of the 38,000 spider species known so far, more than 3,500 make their home in the United States. Of these 3,500 there are only four spiders living in the U.S. that carry venom in large enough doses to hurt a human being. These would be (clockwise below) the Black Widow, Brown Recluse, Yellow Sac spider, and Hobo..

These spiders are the ones you do want to watch out for as their venoms do amazing damage in some cases. But, that's a whole different conversation. The vast majority of spiders don't even have the mandible power to bite through human skin.


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