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Most Dangerous Spiders in California

Updated on May 2, 2017
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Since completing university, Paul has worked as a bookseller, librarian, and freelance writer. Born in the UK, he now lives in Florida.

A female Western Black Widow.  The female of the species is much larger than the male and has by far the most venomous bite.  She is jet black in color and has the distinctive hour glass marking on her lower abdomen, which is typically red.
A female Western Black Widow. The female of the species is much larger than the male and has by far the most venomous bite. She is jet black in color and has the distinctive hour glass marking on her lower abdomen, which is typically red. | Source

There are two types of spider that are capable of delivering life-threatening venomous bites, qualifying them as the most dangerous spiders in California: they are recluses and widows.

The recluse has the worst bite out of the two, but both types can be particularly unpleasant and even deadly in certain circumstances. Both of these spiders live both indoors and outdoors.

You can lower the chances of getting bitten by one of these spiders by:

  • Being able to clearly identify each type of spider
  • Having an understanding of the sorts of places where you are likely to encounter them
  • Taking sensible precautions, such as wearing gloves when reaching into places where you cannot see, such as high shelves and dark corners, particularly in sheds and outhouses.
  • It is also advisable to shake out old clothes, towels, linen, etc. that hasn’t been used for a period of time, before you put them on to wear.

Below is a full description of each spider type, including their common habitats, behaviors, and venomous bites.

Widow Spiders in California

As its name suggests, the Western Black Widow (Latrodectus Hesperus) is found across western regions of the USA.

The females are the ones to look out for when it comes to poisonous bites. They are jet black in color and have the distinctive red hourglass markings on their lower abdomen (although in some cases, the hour glass can be yellow in color, or even occasionally white).

The males are brown to orange in color and generally pretty harmless. The female eating of the male after mating is actually rare in this species and the male often gets to mate numerous times.

Despite their fearsome reputation, widow spiders are timid and will usually run away rather than bite, if they feel threatened.  The only exceptions are when the female is guarding her eggs, or when the spider is pinched against or feels squashed.
Despite their fearsome reputation, widow spiders are timid and will usually run away rather than bite, if they feel threatened. The only exceptions are when the female is guarding her eggs, or when the spider is pinched against or feels squashed. | Source

Widows are nocturnal and build messy looking, three-dimensional webs. They will commonly hang upside down near the center and when they sense an insect getting caught (usually through vibration, rather than by vision), they run over and bite the insect, before covering it in their silk.

Male Western Widow Spider.  The male is much smaller and lacks the powerful venomous bite of the female.  Despite her reputation, the female widow rarely eats the male after copulation, and the male often gets to mate several times over.
Male Western Widow Spider. The male is much smaller and lacks the powerful venomous bite of the female. Despite her reputation, the female widow rarely eats the male after copulation, and the male often gets to mate several times over. | Source

Black Widows have a fearsome reputation when it comes to venomous bites, but the truth is that you are unlikely to die when bitten unless you are particularly old and frail or a young child. Treatment should always be sought straightaway, however.

It should also be noted that Widows are generally timid and will almost always try to run away if they feel threatened. The only exceptions to this are when a female spider is guarding her eggs, or when a Widow is accidentally pinched or pressed against - this can occur when someone puts on old clothing such as a glove or shoe and there is a spider inside it, or if someone is reaching or feeling around in an area where a widow is dwelling, such as a high shelf or dark recess.

Widow Bites

Note that the bite itself may feel like just a small pin prick at the time, or may not even be noticed. Symptoms don’t usually start until 1 to 3 hours after the poisonous bite and may include:

  • Severe pain
  • Headache
  • Muscle and abdominal cramps
  • Nausea
  • Convulsions and tremors
  • Excessive sweating
  • Lesions in the bite area
  • Vomiting
  • Unconsciousness

To start with, the venom just affects the area of the bite, but then it gradually it travels around the body via the lymphatic system, before getting into the bloodstream. Symptoms normally persist for 3 – 5 days maximum. It is extremely unlikely that a Widow bite will be fatal if the victim receives medical treatment.

The Chilean recluse is generally considered to be the most venomous of all the recluse spiders.  Although, as its name implies, it is native to South America, it is known to have established itself in the Los Angeles area.
The Chilean recluse is generally considered to be the most venomous of all the recluse spiders. Although, as its name implies, it is native to South America, it is known to have established itself in the Los Angeles area. | Source

Recluse Spiders in California

Out of the two types mentioned in this article, the recluse generally has the worst bite. The Arizona Recluse, Baja Recluse, Chilean Recluse, Desert Recluse, Martha's Recluse, and Russell's Recluse can all be found in certain parts of California.

As their names suggests, recluse spiders are not aggressive by nature. They tend to bite only when pressed against human skin, for example when an article of clothing is put on which a recluse is living in.

Recluse spiders are generally timid and seldom seen by humans. Bites usually occur when someone reaches or feels around in an area that they can’t see, or when someone puts on an old item of clothing that the spider was hiding in.

Recluse Bites

The effects of a recluse bite can vary enormously, from virtually no effect, all the way up to death (in very rare instances).

Symptoms of a bite typically start between 2 and 6 hours afterwards and can include:

  • Blistering
  • Severe pain
  • Chills
  • Fever
  • Nausea
  • Necrosis at the site of the bite
  • Lesions

Unfortunately, there is no effective antivenom for recluse bites, but medical care should still be found as swiftly as possible.

It should also be noted that most recluse bites are unremarkable.

Recluse bites can vary from an unremarkable bite with mild skin irritation, to severe skin necrosis.  Deep gangrenous wounds can develop and leave deep scars.  Death from a recluse bite is extremely rare however.
Recluse bites can vary from an unremarkable bite with mild skin irritation, to severe skin necrosis. Deep gangrenous wounds can develop and leave deep scars. Death from a recluse bite is extremely rare however. | Source

You can best avoid a recluse bite by:

  • Not leaving clothes, gloves, shoes lying around on the floor, if possible, and shaking them out before you put them on.
  • Not reaching into areas where you can’t see, especially shelves and recesses in sheds and outhouses.
  • Recluses are not naturally aggressive but will react aggressively if they feel that their life is threatened, or they are trapped.

© 2013 Paul Goodman

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    • Anna Marie Bowman profile image

      Anna Marie Bowman 3 years ago from Florida

      I lived in Arizona for four years, and encountered a few Black Widow's during my time, and after seeing the pictures and video of the Brown Recluse, I am pretty sure I came across one of those, as well. Nasty little creatures! Very useful!

    • profile image

      Esteban Vildoso 4 months ago

      Why are you talking about brown recluse spider's they don't live in California.

    • profile image

      Tony Tee!! 4 months ago

      I actually live in Petaluma ca, and work for the garbage company in the north bay and I come across brown recluse spiders, co workers run into them and Heard stories of them being in homes in Santa Rosa as well!!

    • profile image

      Ryan 4 months ago

      Esteban Vildoso actually they have migrated or been brought over to California, in recent years, we used to only worry about widows but now we have the recluse as well, maybe before talking down to someone who gives an informative article do a little research to see if the info you have is still viable.

    • profile image

      exterminator 3 months ago

      Sorry but you are wrong. I am a licensed exterminator who is in the field every day. If you don't believe me, do a google search. The pest control industry, US government & ALL entomolgist/arachnologist agree that there isn't a brown recluse population in California.

      If you are the cynical type (its a coverup!) consider this. Have you ever seen a pest control ad in California for brown recluses? Seems like a pretty big money maker considering the fear-mongering & hysteria... but legally we cannot treat for a target pest if that target pest doesn't exist in our area.

      Think about it and do your own research, don't trust the testimony of that guy at a bar who swears his uncle/neighbor/ex-roommate knew a guy who knew a guy who saw one.

    • profile image

      Mark 3 months ago

      I live in so cal. Once had a server pain in the leg. When I looked it was a large red rash with a small cut. A day later it swelled up and the small cut grew very large. 7 months later I still have a puffy scare. Does that sound like a recluse bite? I look at Google images and it was similar to a recluse, about twice the size of a black widow bite. What do you guys think?

    • profile image

      Scott 3 months ago

      I got bit in 2001 by a recluse while in bed in san diego the bite and spider were identified by Balboa naval medical center so i do believe there just might be recluses in socal

    • profile image

      NorCal girl 2 months ago

      I have personally seen brown recluses and so has my dad. I know for a fact there are some here. Maybe not big populations but they are here. I am not miss identifying them either.

    • profile image

      Dan 2 months ago

      Def seen em in California

    • profile image

      Ralph 8 weeks ago

      If you do some research, there are populations of recluse spiders in the southern deserts of California. But they are not the brown recluse. They could be the desert recluse or the Arizona recluse. They are related but are not the brown recluse.

    • profile image

      Tom 7 weeks ago

      No Brown Recluse in California ....!!!!

      Look up:

      UCR Spiders

      That's:

      University of California, Riverside, Myth of the Brown Recluse

      Tony Tee, check it out and learn how to identify a Brown Recluse.

      Scott, you took the spider to the medical center and they identified it as a brown recluse ....???? So the doctors are also entomologists ....????

      Ryan, maybe you should be doing the research ....!!!

      NorCal girl, you should contact UC Riverside and tell them about your evidence.... !!!

    • profile image

      Tom 7 weeks ago

      The video:

      Clean and repacking brown recluse spider bite;

      Look up the mnemonic, NOT RECLUSE,

      It's not,

      (R)ed,

      (E)levated

      (C)hronic

      NOT RECLUSE—A Mnemonic Device to Avoid False Diagnoses of Brown Recluse Spider Bites

      Authors William V. Stoecker, Richard S. Vetter, Jonathan A. Dyer

      Journal JAMA Dermatology

    • profile image

      pat fox 6 weeks ago

      one of the nations best known spider doctors, also a well know author of all about spiders book, had a standing bet of $25.000 dollars, if some one in calif. filmed and authenticated a brown recluse spider and brought it in , no takers after 2 years, offer canceled, that was 2012

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