Spiders are beneficial predators that help control insect populations, and produce silk and medically useful venom. Because most spiders are beneficial and not harmful, most do not need to be controlled. Some people, however, have allergic responses and severe reactions to venomous spider bites.
Of more than 30,000 species of spiders worldwide, only a small percentage are normally encountered by people. Belonging to the phylum Arthropoda and class Arachnida and exhibiting a vast array of colors, shapes, and sizes, spiders use their coloration for defense, attraction, identification and warning. Beneficial in controlling insect populations, most spiders are relatively harmless and rarely have human contact. Spiders can be found in and around homes, which provide them an abundant insect food source.
Spiders have eight legs and an exoskeleton of two distinct body regions. Young spiderlings emerge from the egg sac and molt a total of four to twelve times, increasing in size with each molt. Most spiders live one or two years.
Living in a wide variety of habitats, spiders use many techniques for attracting, finding and capturing prey. As predators, spiders liquefy their food before eating by injecting digestive fluids into the paralyzed prey and then sucking it dry.
Benefits to humans – In addition to reducing local disease-carrying insects, spiders provide humans with other medical benefits. Spider venom is used in neurological research and may prevent permanent brain damage in stroke victims. The silk produced by spiders is used in many optical devices including laboratory instruments.
The potential harmful effects on human health attributed to spiders are of three kinds – allergic reactions, poison venom and fear.
Spiders may cause an allergic reaction, which occurs when people inhale the hairs or scales of spiders. This recognized allergic reaction is the same type as is caused by other arthropods such as cockroaches.
Spiders may inject venom through their bites in a process known as envenomization. While more than 50 species of spiders are known to be capable of biting humans, there are three – black widow, brown recluse and aggressive house spider – of greatest importance.
The black widow spider injects a neurotoxic venom that causes system symptoms with little or no local damage or necrosis. Symptoms of sweating, weakness, muscle pains, nausea, tremors, and vomiting can, in severe cases, create breathing difficulties, heart irregularities, and even death in those who are weak, such as the elderly and children.
Both the brown recluse and aggressive house spider inject cytotoxic venom which causes severe localized tissue damage and necrosis, but rarely systemic damage. Their bites involve skin loss and ulceration that can take months to heal and may require skin grafts.
Along with snakes, spiders are the most feared creatures on earth. People possess this common fear and in some instances will induce physical illness on seeing spiders.
Begin by identifying the spider involved. Locate where the spiders live and what contributing conditions support the infestation. Remove all potential hiding places inside and outside buildings and improve storage practices. All exterior areas of a building must be secured to eliminate spiders’ entrance.
Insecticides may be used as needed according to label directions on the harmful spiders, their webs and on grounds immediately outside infested buildings. For all products, read and follow label directions.
Start insecticide applications by spot treatment of exposed spiders, typically with a spray product, or with a dust product.
If necessary to treat webs apply dust or liquid insecticides that will leave a residual amount of product to deter rebuilding of webs.
To treat perimeter grounds outside infested buildings, direct hand held pressure sprays or “back pack” sprays are generally the product types used.