Spiders Biology & Control

By |  October 1, 2007

By: Dr. ElRay Roper

Successful spider management requires pest management professionals (PMPs) to practice exclusion and deliver targeted treatment solutions

Spiders are eight-legged arthropods that can become nuisance pests when they are found around residences and businesses. There are an estimated 35,000 species of spiders worldwide, with about 2,500 species found in North America.

Though most spiders are harmless, a few species, such as the brown recluse, black widow, brown widow, hobo and yellow sac spiders, can inflict dangerous bites. A complete understanding of pests’ biology, lifestyle and predatory habits will assist in the most effective control.

Syngenta’s Carol Wyatt-Evens conducts product testing while working with a spider at the company’s Vero Beach. Fla., reserarch facility.

BIOLOGY

Like insects, spiders are arthropods — they have jointed appendages and exoskeletons. Spiders differ from insects in several important ways:

  • Spiders have only two body segments, the cephalothorax and the abdomen, while insects have three distinct body segments.
  • Spiders have eight legs, instead of insects’ six legs.
  • Spiders do not have wings.

In addition to these differences, spiders also produce silk, which they use for a variety of purposes — including capturing prey, constructing harborages, making egg sacs and locomotion (both as drags and as parachutes).

LIFE CYCLES

The average spider lives about two years, although some are known to live up to 10 years. In reproduction, female spiders lay clusters of eggs, which they wrap in silk sacs. The spiderlings hatch inside the sacs, and remain clustered in the sacs for the first few molts. Spiders will molt four to 12 times depending on the species.

Once ready to leave the sacs, the emerging spiders disperse and seek suitable habitats.

THE PREDATORY PEST

Spiders are predators, making them beneficial to humans because they feed on other nuisance pests. Spiders do not have chewing mouth parts. Rather, they have fangs, which are used to inject venom into and immobilize their prey.

Spiders inject digestive enzymes that dissolve muscles and other body parts. They then suck the fluid from their prey.

Spiders may be classified by how they capture their prey. Some spiders, such as the wolf and jumping species, are active hunters that move around in searches for prey. Others, like the brown recluse, are passive hunters, waiting for prey to come to them. Still other spiders, such as the orb species, weave webs to trap prey.

MANAGEMENT STRATEGIES

While fascinating in their diversity of design and beauty of construction, the presence of spider webs around buildings is one of the main customer complaints arising from spider problems.

Also, although most spiders present no danger to people and are usually beneficial in terms of insect management, consumers and business owners do not want to see spiders in or around their dwellings.

Effective spider management requires an integrated approach and the cooperation of property owners. As with any integrated pest management (IPM) program, spider management begins with thorough inspections to identify conducive conditions and the location of spiders and their prey.

Inspect indoors for webs in corners near ceilings, around windows and doors, and behind furniture and other furnishings adjacent to walls. The following steps can help reduce the number of spiders in and around structures:

  • Seal cracks and openings around the structures.
  • Repair screens on doors and windows.
  • Install weather stripping on doors.
  • Ensure proper ventilation in crawlspaces and attics to reduce excess moisture.
  • Use sticky traps to monitor spider activity and trap them indoors.
  • Vacuum webs and spiders from harborages. Be sure to seal and dispose of vacuum bags immediately.
  • Thorough and regular house and office cleaning will help discourage spider activity indoors.
  • Redirect or change outside lighting to draw insects away from the building. The use of sodium vapor lights or yellow lights will reduce the number of insects attracted to the lights and discourage spider activity.
  • Modify environments by pruning and cleaning the landscape to reduce harborages for spiders and insect prey.
  • Remove debris, and move woodpiles away from the structures.
  • Remove boxes and other stored items from garages and indoor areas to reduce harborages

Insecticide application can be an effective tool in reducing spiders and their insect prey.When making insecticide applications for spider management, it’s important to remember the following points:

  • Many water-based sprays will not stick to spider webs, so spraying the webs with these often will not result in long-term control of the spiders.
  • Before treating, use a small broom or vacuum to remove spider webs.
  • Pay particular attention to areas around entryways, patios, porches and windows..

LONG-TERM MANAGEMENT

Returning spiders generally will try to reconstruct their webs in the same locations. Apply insecticide to the areas where webs were attached to the structures. The spiders may return and encounter the treatment.

In areas where webs aren’t present, target sprays to probable spider harborages around doors and windows, and in cracks and crevices.

The spiders are present because they are feeding on insects around the buildings. Help eliminate that food source with a general perimeter application to reduce insect levels.

When selecting an insecticide for interior spider work, keep in mind that some treatments will not provide effective residual control on porous surfaces. Microencapsulated pyrethroid insecticides stay on top of porous surfaces and adhere well to the spider’s legs.

Wettable powder formulations of pyrethroids also are proven performers for spider management, and will maintain effectiveness on porous surfaces.

Roper, a senior technical representative for Syngenta Professional Products, holds a Ph.D. in urban entomology from North Carolina State University. For more information on spider management technologies and techniques, visitwww.securechoice.us or e-tmail pmpcontributor.com.

This article is tagged with and posted in Black Widow Spiders, Brown Recluse Spiders, Invasive/Occasional Species, Spiders

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