Boise Idaho Pest Information: Spiders

Spider Identification

Idaho is home to many different types of spiders of all different sizes, shapes and colors. Some of them can even be very poisonous and could require medical attention after a bite! Unlike insects, spiders have eight legs and are in the arachnid family along with mites and ticks. Spiders can live in almost any habitat. Below are some of the most common spiders in our area.

Black Widow Spider

Black widow spiders are a venomous spider found in Idaho and our service area. The female black widow is easily identifiable with her black body and reddish hourglass shape on her abdomen. Males are lighter in color with a median row of red spots with white lines radiating out to the sides. Immature black widows are usually orange and white, turning black as they mature, with 1 or 2 reddish markings on the abdomen. Outside, black widows are commonly found in protected areas under firewood, decks, in hollow stumps, rodent burrows, etc. They are also frequently found inside barns, sheds, henhouses, meter boxes, barrels, etc. Indoors, black widows can be found in seldom used areas of basements, crawlspaces, and garages. It is a very poisonous spider, and if bitten, medical attention should be sought immediately. The venom is a neurotoxin and should be treated with an antitoxin.

Biology and Behavior
  • Glossy black in color with a distinct reddish-orange hourglass shape on the belly.
  • Eight eyes arranged in two rows of four.
  • Females can be approximately 1-½ inches around when their legs are fully extended.
  • Males are about half of their size and generally considered harmless since they will very rarely bite a human.
  • Frequently found in sheds garages basements crawl spaces and woodpiles.
Brown Recluse Spider

Identifying features of the Brown Recluse spider include a brown-to-gray abdomen, lighter coloring on the legs, and an orange-to-yellow cephalothorax. The area at the head and eyes has what appears to be violin-shaped birthmark on top of it (see photo). The round bottom of the ‘violin’ sits over the eyes, and the skinny neck of the ‘violin’ points back toward the abdomen. Every Brown Recluse has that violin-shaped marking, but some people believe they see it on other, harmless spiders causing unnecessary confusion and panic.  The six eyes are in tight pairs, with one pair in the front center of the face and the other two pairs flanking the sides.

These spiders generally inhabit loose piles of debris outside. If indoors, they may be found lying on or inside furniture as well as within undisturbed clothing. Many bite victims put on clothing that was left on the floor, and are bitten by the frightened spider hiding inside. This spider is not naturally aggressive and does not seek out human victims.

Biology and Behavior
  • Adult brown recluse spiders are usually about 1/4 to 1/2 an inch in body length with a total leg span of 1 ¼ to 2 inches.
  • These spiders are tan to dark brown with a darker fiddle-shaped marking on top of the cephalothorax (body segments where legs are attached).
  • Recluses have 6 eyes uniquely arranged in 3 groups of 2 (diads) in a semicircle.
  • Recluses prefer to inhabit undisturbed areas such as attics crawl spaces basement closets areas under furniture and inside wall voids.
  • Male recluse spiders and juveniles are most often seen. Females generally stay well hidden making them more difficult to eliminate.

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