Poisonous Spiders in the Home: Pictures and Tips

picture of a Brown Recluse spider

In North America, three spiders, the brown recluse spider, the hobo spider, and the black widow spider (Latrodectus species) cause much of the fear of spiders so apparent in segments of the population.

Technically they are know as spiders of medical importance because their bites can be a cause of medical concern. Less formally they are known as poisonous spiders.

The brown recluse spider (Loxosceles reclusa), a resident of many Southeast and Midwest states, makes the human population in these areas wary of any brown spider they come across.

While they come in a variety of shades of brown, the violin marking on the cephalothorax serves as the best field identification clue. Additionally, the legs do not have bands.

The common name recluse is important. Like other spiders, they are typically an outdoor species that shy away from human contact. Problems typically arise when males wander indoors and a human inadvertently gets bitten.

In more severe cases, a brown recluse female establishes a nest within a house. Usually they are found in garages, crawlspaces, attics, wall voids and the like.

In these instances, a house can become infested. Females lay eggs in flattened egg sacs that are frequently attached to the underside of objects. Up to 40 spiderlings may hatch from a single egg sac. A single female may produce up to five egg sacs in a summer.

According to the Center for Disease Control (CDC):

The brown recluse spider cannot bite humans without some form of counter pressure, for example, through unintentional contact that traps the spider against the skin. Bites may cause a stinging sensation with localized pain. A small white blister usually develops at the site of the bite. The venom of a brown recluse can cause a severe lesion by destroying skin tissue (skin necrosis). This skin lesion will require professional medical attention.

Medical professions suggest that individuals concerned about the possibility of Brown Recluse bites, should attempt to capture the spider and bring it with them when they seek medical attention. Brown Recluse bites are rare. When they do occur, an article in the Annals of Emergency Medicine notes,

“In our series, long-term outcome after brown recluse spider bite was good. Serious complications were rare, as was the need for skin grafting. Because the vast majority of bites heal with supportive care alone, aggressive medical therapy does not appear warranted.”

See also: Reports of Presumptive Brown Recluse Spider Bites Reinforce Improbable Diagnosis in Regions of North America Where the Spider Is Not Endemic

Hobo Spider

picture of a Hobo Spider, part of the poisonous spiders series The Hobo Spider (Tegenaria agrestis), a recently introduced species to the United States, coming from Europe to the Pacific Northwest also receives attention in the medical literature.

Often Hobo spiders get placed in the poisonous spiders category. The research on Hobo Spiders is incomplete, and no definitive answer regarding their level of danger exists. Common sense suggests that since the Hobo spider was never a spider of medical concern in Europe for hundreds of years, its introduction into the United States did not change the toxic level of its bite.

Still a spider bite is a spider bite and since they are in the home, there’s always reason for a bit of concern.

Most experts warn against using a picture for a definitive spider identification, including the Hobo Spider. Given that fact, the first picture in this shows a spider that has many of the Hobo Spider’s physical characteristics. There are no bands on the legs and the abdomen has a “v” pattern down the middle (the “v” is upside down in the picture).

picture of a Giant House Spider
The Hobo Spider belongs to the funnel web spider family (Agelenidae), and the two spinnerets extending from the bottom of the abdomen are characteristics of funnel web species. Like other funnel web spiders, they prefer the outdoors, and tend to come indoors during the late fall, as the season changes. Wandering males also are known to wander through the house.

Compare it to the second picture, the Giant House Spider. They are both Pacific Northwest species in the same genera. Giant House spiders can grow up to four inches in length (legs included).

Poisonous Spiders: Black Widow Spider

picture of a Black Widow Spider, part of the poisonous spiders series
Most people refer to the species in the genus Latrodectus as black widow spiders or widow spiders. Along with the recluse spider and hobo spider, Latrodectus species are considered spiders of medical importance in the United States.

Using the language of spider talk, Latrodectus belong to the larger cobweb spider family, Theridiidae. Five Latrodectus species live in North America:

  • Latrodectus bishopi: Red Widow
  • Latrodectus geometricus: Brown Widow
  • Latrodectus hesperus: Western Black Widow
  • Latrodectus mactans: Southern Black Widow
  • Latrodectus variolus: Northern Black Widow

The bite of females contains a neurotoxin that can cause severe health problems, and at the extreme end, death.

Symptoms appear about an hour after the initial bite and can include nausea, shortness of breath and chest or abdominal pains. Anyone suspected of being bitten should immediately seek medical attention.

Latrodectus species typically live in and around residential areas, predominantly in the southern half of the United States, although the range of both the Northern and Western species extends into Canada. With legs extended, widow spiders can measure up to an inch and one-half in length. Any corner of a wood pile, basement or porch provides sufficient space for the female to build a tangled looking, untidy web.

The traditional description of female widows begins and ends with their dark black bodies and red hour glass marking on the underside of the abdomen.

Yellow Sac Spider

picture of a Yellow Sac Spider
The Yellow Sac Spider or Longlegged Sac Spider (genus Cheiracanthium, family Miturgidae) fits one rung below the poisonous spiders category that is often reserved for the Black Widow, Hobo Spider and Brown Recluse spider.

Small in stature (less than one inch in length), their bite is known to cause immediate severe pain, followed by redness, swelling and itching. Current medical literature suggests necrosis is not a symptom of yellow sac spider bites. So, while their bites may be nasty, they are not known to produce medical complications.

Two different species live in the United States, C. inclusum, a native species found throughout most of the United States, and C. mildei, a European species with established populations in much of the Northeast and Northwest.

Both species share similar physical characteristics which are visible in the top picture. The body is a light color with little marking other than a light stripe on the abdomen and the front pair of legs are longer than the other three pair of legs.

Both species are also known to inhabit residential areas, which makes them candidates for wandering around the house or apartment.