dos and don’t: Spiders

Although unpopular, most spiders are cryptic and inert to humans, and have chelicerae (mouthparts) too small or weak to puncture human skin. Usually, spiders won’t attempt to bite unless accidentally trapped or held. The jaws of the spider suborder Araneomorphae are slung vertically under the front of the carapace. The jaws are tipped with fangs that can inject venom or digestive secretions (located below the eyes). The fangs are hinged laterally and bite crossways against each other. This is an efficient arrangement for seizing and manipulating prey, especially on a web. Next to the jaws, to taste food, are its pedipalps, which are sensory appendages. Male spiders have an enlarged segment on the tip of the pedipalps, which are copulatory organs that transfer sperm to the female.

The pedicel, or waist, connects the cephalothorax and abdomen. The cephalothorax, or fused head-thorax, contains the spider’s brain, eyes, jaws, stomach and leg attachments. Its abdomen contains its guts, heart, reproductive organs and silk glands. Spinnerets are where spider’s silk is released. The spider’s eyes, which detect only light and dark, are located on top of the cephalothorax. Most have eight eyes, but it’s possible to have 12, six, four, two or none. Its legs consist of seven segments, with two or three claws at the tip. If a leg is lost, it’ll grow back.

Treatment strategies

Most spider species are beneficial because they eat harmful insects and mites in and around structures, so, when possible, don’t unnecessary destroy spiders. Other tips are:

• Do interview your client to gather detailed information about spider pressures and possible sources. Take notes.
• Don’t overlook any detail provided in Q&A discovery with your client because the smallest detail will be important to a successful intervention.
• Do maintain sodium vapor (yellow) exterior lighting to reduce night-flying insects that attract spiders.
• Don’t maintain mercury vapor (blue) exterior lighting if possible because it’s 112 times more attractive to flying insects.
• Do use high-pressure water to knock down and destroy webs, egg sacs and spiders.
• Don’t allow woodpiles, trash, rocks, compost piles, old boards and debris to collect along exterior structural areas because they can harbor spiders.
• Do eliminate moisture and humidity by keeping basements and crawlspaces as dry as possible, through ventilation and dehumidification.
• Don’t allow a buildup of webs, egg sacs and spiders. Use a vacuum cleaner with the proper attachments to access difficult-to-reach areas. pmp

Dr. Mitchell, D.O., Ph.D., M.P.H., B.C.E., a board-certified physician and entomologist, is principal technical specialist for PestWest Environmental, as well as PMP’s Technical Editor. He can be reached at docmitchell@northcoastmedia.net or 515-333-8923.