Black Widows

Southern black widow spiders (Latrodectus mactans) and western black widows (Latrodectus hesperus) are common indoor or perimeter pests. Their bites are venomous and the neurotoxin they inject can cause pain, nausea, cramping, and occasionally, serious health effects.

If you have been bitten by a spider that you suspect is a black widow, contact your doctor or go to an urgent care center to determine if you require medical attention. 

Thankfully, black widows aren’t inherently aggressive - they’re actually pretty shy. Usually, we’d recommend that most spiders be left alone - many don’t directly harm humans, and can actually help reduce other pest populations. But because black widow bites are venomous, it’s important to be able to identify and prevent black widow spiders in and around your home.

How to ID Black Widow Spiders

Like all spiders, black widows have eight legs and two main body parts. Black widows can often be confused with other black spiders, but their markings are the best ID tip. 

Immature females are pale brown or black, with white or orange striping. Adult female southern black widows are glossy black and about ⅓-½ inch long with a leg span of around 1 ½ inches. Southern black widows have a characteristic red hourglass shape on the underside of their abdomen.

 

Western black widows are similar in size and shape, but their hourglass marking can be “broken” and can be yellowish to red in color. Male black widows of both species are generally smaller and lighter in color, and resemble immature females.

Sunday Fun Fact: Despite their ominous name, female black widow spiders rarely eat the males after mating. This only happens if other food is scarce.

Where do Black Widows Live?

Southern black widows are found in the western and southern US, while western black widows are found in the western US. 

Outdoors, black widows can commonly be found in dark, protected places such as:

  1. Around building foundations
  2. In irrigation control boxes 
  3. Near exterior lighting
  4. In rock or wood piles

Black widows will enter homes via gaps and cracks around doors or other openings to avoid cold weather or to find food. Indoors, they are most commonly found near the ground, often hiding in dark corners or in basements.

When are Black Widows Active?

Black widows are most active when temperatures get above 50°F. Usually, they will hide during the day and be active on their webs at night. While black widows aren’t particularly aggressive, females will become territorial when protecting their egg sacs.

Natural Pest Prevention and Reduction Practices

Despite their generally docile nature, black widows can be scary to run into. To avoid an unexpected encounter, we recommend the following:

  1. Before sticking your hands into dark spaces, check for black widows – they can hide in areas like wood or rock piles, animal burrows, and even under patio furniture, garden pots, or outdoor grills.
  2. If you do need to do some work in those dark spots, wear thick gloves and long sleeves to protect yourself.

 

Stop these spiders from entering the home by taking preventative measures:

  1. Minimize nesting habitat like wood or rock piles or small animal burrows.
  2. Seal exterior cracks and crevices and minimize indoor and outdoor clutter to reduce hiding places.
  3. Install door sweeps and tight-fitting window screens. 
  4. Change exterior lighting to sodium vapor bulbs.

Sunday pest control products are not labeled for black widow control. If black widows do make their way into the house, you can get rid of them by vacuuming individuals and webs. Make sure to also reduce any other insect and insect-like pests that may serve as a food source.

Cited Sources

Cranshaw, W. Western Widow Spider. Colorado State University. 

USU Extension. Black Widow Spider. Utah State University. 

Hu, X.P., F.M. Oi and T.G. Shelton. The Black Widow. Alabama Cooperative Extension System.