Latrodectus Hersperus – Western Black Widow

Latrodectus hesperus, the Western black widow spider is one of the few medically significant venomous spiders in the United States. As its common name suggests, it can be found in the Western States of the US as well as in Canada.

Description of the Western Black Widow

The larger female Western black widow looks very similar to the Northern black widow and the Southern black widow female. The best indicator for a western black widow is the geographic location. If you spot a black widow spider in California or on the Northern Pacific Coast, you are most likely looking at a Western widow spider.

Hourglass spider black with red long legs black widow
An adult female Western black widow hanging upside-down in its web. Photo: Andrey Zharkikh

The adult female western black widow has a completely black and shiny body with an orange or red hourglass-shape at the bottom. The hourglass is complete and not broken in the middle as is the case for the northern black widow.

The immature female’s body is often more a very dark brown instead of completely black. While the hourglass at the dorsal side of the abdomen is already visible, the upper side of the abdomen has some brown and yellow markings.

latrodectus hesperus western black widow juvenile female spider
An immature female Western black widow. Photo: Louis

The male is considerably smaller than the female and its body is brown and olive green with orange markings on its abdomen. Juvenile and male black widows do not inject enough venom with a bite to cause serious medical effects.

western black widow male adult
The male western black widow looks nothing like the female. But it is also not medically significant. Photo: Matt Maves

Western black widows are often confused with the closely related Steatoda grossa spider which led to its common name false black widow. Especially in California, the Steatoda grossa population has exploded over the last years leading to many mistaken identifications.

Size

All North American widow spiders are roughly the same size. The adult female black widow grows to about half an inch (13mm). They can reach a total legspan of 1.5-2 inches (38-50mm).

Web

Widow spiders create very erratic webs. Mostly, the webs can be found in corners and look like loose strands of web. The female will spend most of its time in or very close to the web. If you see an unprofessionally looking, small web, you might be dealing with a widow spider. Don’t reach out to touch the web with your hands. This might scare the spider and cause it to attack. Especially if the web contains egg sacs. Most of the reported black widow bites occur to the limbs, especially hands.

Latrodectus hesperus Western black widow spider venomous spiders in the United States
An adult female Western widow spider in its erratic web. Photo: Matt Maves

Western Black Widow Bite

Western black widows aren’t aggressive spiders. Most likely, it will run away from you before it would even get the chance to bite you. However, if the spider feels trapped or attacked, it might feel no other option than to bite. Black widows often bite without injecting any venom into the target. This means that the bite is harmless apart from the mild pain from the actual bite. We still recommend to visit a doctor or a hospital if you have been bitten by a female black widow spider. Even though some bite feel minor at first, the venom can cause nausea, vomiting and other symptoms after some time.

Range of the Western Widow in the United States

Western Black Widow Range USA Map
The range of the Western Black Widow in the United States

The Western Black Widow can be found throughout the Southern and Western states of the US. Namely, these are the following states: Washington, Oregon, California, Nevada, Utah, Arizona, New Mexico, Colorado, Nebraska, Kansas, Oklahoma, Texas.

Scientific Classification of Latrodectus hesperus

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Subphylum: Chelicerata
  • Class: Arachnida
  • Order: Araneae
  • Infraorder: Araneomorphae
  • Family: Theridiidae
  • Genus: Latrodectus
  • Species: Latrodectus hesperus
Latrodectus Hersperus – Western Black Widow

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