Spiders in the home
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 (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 (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 (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 (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 (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.
- The most common spiders in Colorado homes are western black widow spiders, funnel web spiders, cellar spider, wolf spiders, ground spiders, woodlouse spiders, jumping spiders, and yellow sac spiders. Only the western black widow spider poses a significant threat to human health, while yellow sac spiders are believed to inflict most in-home bites. Brown recluse spiders are rare in Colorado due to the cold winters and dry climate. Bites from the brown recluse are over-diagnosed and rarely accurate.
- Most spiders are not aggressive and will not bite unless provoked and in close contact with the skin, or if their nest/egg sac is disturbed.
- Spiders are not commonly a nuisance pest and are usually beneficial arthropods as they consume insects. To prevent spiders from entering the home, it is recommended that homeowners seal any potential entry points and remove suitable breeding sites such as wood piles, compost, rocks, and any other shelter-type sites in or around the home.
Agelenopsis sp., a species of funnel weaver. Note the funnel shaped web. There are a variety of species in different families that can occur in and around homes in Colorado. Most are harmless, with the exception of the western black widow spider. Image credit: Joseph Berger, Bugwood.org
Western black widow spider. Note the characteristic red hourglass shape on the underside of the abdomen. Image credits: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Hogna permunda, a species of wolf spider. Note the light brown coloration. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
A species of cellar spider (Pholcus sp.). Note the long, slender legs and two distinct body segments. These spiders are often confused with harvestmen due to their long slender legs. Image credit: Joseph Berger, Bugwood.org
A species of ground spider (Herpyllus ecclesiasticus). Note the conspicuous spinnerets at the end of the abdomen. Image credits: Joseph Berger, Bugwood.org
A species of woodlouse spider (Dysdera crocata). Note the smooth body, large fangs, and red/orange cephalothorax and legs. Image credit: Joseph Berger, Bugwood.org
Phidippus audax is a species of jumping spider known to occur in Colorado homes. Note the large eyes. Image credits: David Cappaert, Bugwood.org
Yellow sac spider (Cheracanthium inclusum). Note the pale colored body. Image credits: Joseph Berger, Bugwood.org
Adult of Araneus gemmoides. Note the large, dimpled abdomen and light brown coloration. Image credit: Eugene E. Nelson, Bugwood.org
Adult of Argiope trifasciata. Note the silver body with yellow and black stripes. Image credit: Dani Barchana, Bugwood.org
Female yellow sac spider (Cheracanthium inclusum) with a seven-day old egg sac. Image credits: Joseph Berger, Bugwood.org
Life history and habits
The life cycle of spiders depends on the species, but most spiders found in Colorado have a one-year life cycle. However, some spiders such as the western black widow spider and wolf spiders can live for multiple years. Eggs are laid in clusters of up to several dozen and most are covered in silk. After emerging from the egg sac, most spiderlings disperse by ballooning, in which the immature spider climbs to the top of a tall, nearby object and releases a strand of silk to catch wind currents. This method of dispersal is very effective, and spiders can travel long distances with ballooning. Males are more likely to be found in homes.
Spiders are typically not aggressive toward humans and only bite when their nest is disturbed or when trapped in contact with skin. If bitten by a spider, it is recommended to treat the site with antiseptic to prevent infection and apply ice to reduce swelling. Correct identification of the spider is important in the case of western black widow spiders to administer potentially lifesaving antivenins. Although diagnosing spider bites is extremely challenging, most are not harmful to humans beyond physical pain and discomfort.
Spiders in the home are usually beneficial as they eat other pestiferous arthropods. Removing habitats that are suitable breeding sites for spiders should be the priority. These include wood piles, compost, rocks, and any other shelter-type sites in or around the home. Keep basements, crawl spaces, or other dark areas clean of clutter and vacuum regularly. In addition, the removal of other insects and arthropods will deter spiders from your home by eliminating their food source. Caulking cracks near baseboards, doors, etc. are also an effective way to keep spiders from entering the home.
When found in homes, spiders can be removed by hand with protective gloves, trapped in a container, or vacuumed. Placing sticky traps for cockroaches and rodents can be effective when placed along migration areas such as baseboards.
Chemical control is not the most effective mechanism unless it is paired with cultural control mentioned above. Insecticides can be used in corners of rooms and other areas where spider might breed and create a web.
Colorado State University (n.d.). Funnel Weaver Spiders. Colorado Arachnids of Interest. Available http://www.wci.colostate.edu/Assets/pdf/CIIFactSheets/FunnelWeaverSpiders.pdf
Colorado State University. (n.d.). Jumping Spiders. Colorado Arachnids of Interest. Available http://wci.colostate.edu/Assets/pdf/CIIFactSheets/JumpingSpiders.pdf
Colorado State University. (n.d.). Wolf Spiders. Plant Talk Colorado. Available https://planttalk.colostate.edu/topics/insects-diseases/1485-wolf-spiders/
Cranshaw, W. 2014. Indoor Spiders of Colorado. Colorado State University – Extension. Available https://webdoc.agsci.colostate.edu/ipm/IndoorSpider1.28.14FINALincl.Acknowledgements.pdf
Peairs, F., W. Cranshaw, and P. Cushing. 2013. Spiders in the Home. Colorado State University – Extension. Available https://extension.colostate.edu/topic-areas/insects/spiders-in-the-home-5-512/
Utah State University. 2013. Spiders: Management Tools for a Healthy Learning Environment. Available https://extension.usu.edu/pests/uppdl/files/ezplug/uploads/Spiders_2013PP.pdf