The 4 Poisonous Spiders Found in Missouri! (ID Guide)
Luckily, there are ONLY four types of poisonous spiders in Missouri!
And fortunately, they only bite when disturbed or provoked. It’s important to remember that spiders would rather run away from you than bite. If you come across one of the spiders listed below, please DO NOT DISTURB!
Did you know that spiders are considered venomous, NOT poisonous?
There currently is a common misconception between poisonous and venomous, one is ingested, and the other is injected. So, for example, If you eat something that makes you sick, then it is considered “poisonous.” But if an animal, like a spider, delivers its toxins when it bites, then it’s considered “venomous.”
*WARNING – If you are bitten and think the spider is venomous, please go to the hospital!
If you have an allergic reaction, do not use this article to try to identify the spider. If possible, it is beneficial to capture the spider that has bitten you so the correct treatment can be determined.
Also, since spiders are predators, please know that every single species you come across can bite. And you may have a slight allergic reaction to many of them which are not on this list. For today’s post, I tried to focus on venomous spiders known to be very dangerous to humans when they do bite.
Also, if you enjoy this article, make sure to check out these other Missouri guides!
4 Venomous Spiders That Live in Missouri:
#1. Black Widow
- Females are 1/4 to 3/8 inches long—shiny black with distinctive red hourglass-shaped mark. A row of red spots is visible above.
- Males are half the size of females but have longer legs.
- Bristles on their hind legs that they use to cover their prey with silk once it has been trapped.
Black Widows are the most venomous spider in Missouri!
In addition, they are probably the most popular and recognizable spider in the world. Almost everyone can recognize the red-shaped hourglass mark that appears on the females.
Black Widow Range Map
But here’s the good news:
Even though they have highly toxic venom, 15 times stronger than a rattlesnake, they are not aggressive animals. The Black Widow only bites defensively if the web is disturbed, and they RARELY bite humans.
But, if you are one of the few unlucky people who bitten each year, you should know that the venom affects your nervous system. Some people are only slightly affected by it, but many have a severe response. If you are bitten, the bite requires medical attention, and the neurotoxic venom can be fatal to small children if untreated.
Black Widows prefer dimly lit locations, dark corners in a basement, closets, and cluttered areas.
The best places to look for them include overhanging ledges, under benches or other objects, barns, garages. Also, under stones, near entrances to abandoned rodent burrows, or around outbuildings. They don’t like moisture and prefer dry areas.
Black Widows have a bizarre mating ritual. It begins with the male coming to the female’s web and destroying it. This reduces the female’s pheromones and makes the web less attractive to other males.
The females do not seem to mind the destruction of their property, and it even seems to make them more receptive to mating. Even so, sometimes, the female kills and eats the male after mating. This gruesome behavior is what gave these poisonous spiders their name.
#2. Brown Widow
- Latrodectus geometricus
- Females are 1/4 to 5/8 inches in length—light brown spider. The abdomen has an orangish hourglass-shaped mark on the underside.
- Males are roughly half the size of females. Look for an orange spot on the underside of the abdomen that may be broken into two spots.
- The legs on both sexes are light brown with dark near the joints.
- Also known as the Grey Widow
These venomous spiders are not native to Missouri.
Brown Widows are believed to have originated in either Africa or South America. But now, they are found across the world, typically near buildings in warmer areas.
Brown Widow Range Map
In areas with both species, it seems to researchers that Brown Widows are outcompeting and potentially displacing Black Widows. And while Brown Widows have dangerous venom, it’s less toxic than a Black Widow.
In addition, they are timid and seldom bite. In the rare case that a bite does occur, the symptoms include high blood pressure, sweating, vomiting, respiratory muscle weakness, and possible seizures. Sometimes you can develop a very stiff abdomen that may mimic appendicitis. The worst pain is generally in the first 8-12 hours.
#3. Brown Recluse
- Loxosceles reclusa
- Both sexes are .25 to .375 inches long.
- Yellowish to grayish brown. The head is often darker, usually with faint or distinct violin-shaped marks.
- Long legs.
- Also known as Violin Spider or Fiddle Back.
These venomous spiders can be found in Missouri both outdoors AND indoors.
Yes, you can’t even escape them in your house, as Brown Recluses are commonly found in homes and buildings. They prefer dimly lit locations, like dark corners in a basement, closets, cluttered areas, or even inside your shoe or bed!
Brown Recluse Range Map
Many people regard the Brown Recluse as more dangerous than the Black Widow.
Everyone knows exactly what a Black Widow looks like with their distinctive red-hour glass shape on an entirely black body. But a Brown Recluse looks like many other common types of house spiders. So instead of treating them with caution and respect, most people don’t even know they have encountered a dangerous venomous spider!
Luckily, Brown Recluse bites are rare and only bite you if provoked.
Unfortunately, since they live indoors, bites often occur when you accidentally step or roll on them while sleeping. The bite is painless, so you may not even know you have been bitten until later.
Watch the above video to see the damage a Brown Recluse bite can cause!
Bites can result in lesions, nausea, fever, and wounds that are slow to heal, becoming necrotic and sometimes causing secondary infections. Necrosis (death of cells) sets in quickly, and the result is an excruciating and gruesome “flesh-rotting” wound.
#4. Black-Footed Yellow Sac Spider
- Cheiracanthium inclusum
- Pale yellow-beige color with dark brown markings on its palps, jaws, and on the ends of its feet.
- There is also often an orange-brown stripe running down the top center of its abdomen.
- Also known as the American Yellow Sac Spider. As you can see, it gets its name from its appearance.
Yellow Sac Spiders are venomous and capable of biting humans.
Their bite begins with a bit of pain followed by itching and swelling. Symptoms from the bite typically are gone within 7-10 days. On the bright side, Yellow Sac Spiders rarely bite!
Black-footed Yellow Sac Spider Range Map
The severity of a Yellow Sac bite is not nearly as bad as a Black Widow or Brown Recluse. A study of twenty confirmed Yellow Sac Spider bites found that none resulted in necrosis (decaying of tissue due to cells dying). Instead, it seems like their bites cause swelling.
These venomous spiders are most often found in Missouri on the foliage of trees and shrubs. But it’s not out of the question to find one in your house or other manufactured structures. Unfortunately, it’s fairly uncommon to actually see a Yellow Sac Spider unless you’re actively searching for one. The reason is that they are nocturnal and only come out at night to feed and mate.
Lastly, in 2011, Black-footed Yellow Sac Spiders caused quite a big problem for Mazda. In fact, the automobile company had to recall 65,000 Mazda 6 vehicles after they found webs from this species were clogging fuel system ventilation tubes. It seems that the spiders are attracted to the smell of gasoline, but it’s unclear why ONLY this particular model was affected!
Do you need additional help identifying a venomous spider?
Try this field guide!
Which of these venomous spiders have you seen in Missouri?
Leave a comment below!