Spiders in the home

Order: Araneae

Description

Western black widow spider 
Western black widow spiders, Latrodectus hesperus, (Family: Theridiidae) are the most dangerous spider found in the home. They can inflict a painful and potentially harmful bite, with young children and the elderly among the most susceptible individuals. Both male and female western black widow spiders have the characteristic hourglass shape underneath their abdomen. The hourglass is red on females and orange or yellow on males. Adult females typically have black bodies and are 6.4-8.5 mm (1/4-1/3 inch), while males tend to have brown bodies with striped markings and are 3.2-6.4 mm (1/10-1/4 inch). For more information on western black widow spiders, consult the webpage.

Funnel weaver spiders
Funnel weaver spiders (Family: Agelenidae) create funnel shaped webs. They are the most common spiders in homes, typically found in the early fall when temperatures start to cool. These spiders are harmless to humans. When fully grown, they can reach lengths of 8.5-17 mm (1/3-2/3 inch). They create protective mats of silk in vegetation for shelter, which they can retreat into when threatened. They vary in color, size, and shape but usually have four pairs of eyes that are the same size. These spiders are commonly misidentified as species in the family Lycosidae.

Wolf spiders
Wolf spiders (Family: Lycosidae) usually do not enter homes unless their habitat is disturbed. They do not create a web to capture prey, but can create a silk retreat in protected areas such as under rocks, in soil, etc. When fully grown, they can reach lengths of 1.3-5 cm (1/2-2 inches). Most are brown or gray and vary in size and appear hairy. Larger species can bite humans, though their bite does not pose a health risk. Small species are commonly misidentified as funnel weaver spiders. Interestingly, females carry the egg sac on spinnerets at the rear of the abdomen. When hatching, the spiderlings will remain on the mother’s back for the first few weeks.

Cellar spiders 
Cellar spiders (Family: Pholicidae) have long, narrow legs and are often confused with harvestmen. These spiders have bodies around 8.5 mm (1/3 inch) but can appear much larger due to their long legs. Their webs are usually irregular and sticky, built in corners of buildings and dark areas.

Ground spiders
Ground spiders  (Family: Gnaphosidae) can enter homes when temperatures drop but are completely harmless to humans. These spiders are small, typically measuring less than 1.3 cm (1/2 inch). Outdoors, ground spiders live under logs, rocks, or in the soil. Like wolf spiders, they also build silk retreats in the soil.

Woodlouse spiders
Woodlouse spiders (Family: Dysderidae) have smooth bodies with distinctive red/orange legs and thorax and conspicuous large fangs. Their venom is not dangerous to humans, but they can deliver a painful bite. Their bodies measure about 9-15 mm (1/3-2/3 inch) in length.

Jumping spiders 
Jumping spiders (Family: Salticidae) are small or moderate in size, measuring about 4-12 mm (1/6-1/2 inch) and can be brightly colored or shades of black, brown, or gray. They are active hunters that can jump short distances to capture prey. They are not pests in the home, and while some species occasionally enter the home, they are not a threat to humans.

Yellow sac spiders
Yellow sac spiders  (Family: Miturgidae) commonly live and breed in homes, especially in the fall. They are usually found in silk webs in the corners of homes, near the ceiling or in wall cracks. These spiders are mostly pale in color and measure about 6 mm (1/4 inch) in length. Their bite is painful but usually does not cause any side effects. They are thought to be the cause of most in-home spider bites in Colorado.

Orb weaving spiders 
Orb weaving spiders (Family: Araneidae) are commonly found outdoors and are harmless to humans. They create spiral, wheel shaped webs. Araneus gemmoides is the largest and most encountered species in Colorado. This species is light brown and has a large, dimpled abdomen with markings. Females can reach diameters of up to 2.5 cm (1 inch). Another common species, the banded garden spider (Argiope trifasciata), can be found in shrubbery and gardens in the late summer and early fall. Females have silver bodies striped with yellow and black.