Poisonous Black Widow Spiders – facts, webs and identification

dangerous harmful widow spiders

What do you do when you find a Black Widow Spider?  Although spiders are important for the ecosystem and very beneficial to a garden, widow spiders are considered the most venomous spiders in North America.

Latrodectus, western widow spider poisonous
large female black widow with the red hourglass marks

Black Widow spiders are the most common species that belong to the Latrodectus genus, in the Theridiidae family. 

The web of a widow spider, Latrodectus,  looks like it was haphazardly thrown together.  The photo below shows silk strands grouped together with bits of leaves and sticks in the web.

black widow spider web photo
web of the black widow spider is tossed together with strands of silk

Black widow spiders tend to make their webs close to the ground in undisturbed areas.  The female widow spider is quite the homebody and likes to stay in her web.

Latrodectus genus of spider, in the family Theridiidae
a young spider and female black widow spider

Juveniles and adult male Latrodectus are much smaller than the female spiders and are a light brown or grey color.  Usually the male widow spider has several red, orange marks on his belly along with yellow or white bands on the top of the abdomen.


Latrodectus is a genus of spider which has 32 species, with varying markings and colors. The more common name is WIDOW SPIDERS.

Widow spiders belong to the cobweb spider family. They spin unorganized, irregular, messy webs to catch insects.

The black widow spider is shy and rarely leaves the web.  She prefers to make her home in dark, protected areas. Being nocturnal, this spider does its hunting at night.

spider with red marks
female widow spiders are larger than the males

It is wise to be cautious of this poisonous spider! Widow spider bites are dangerous because of the neurotoxin that causes the condition latrodectism – which is seizures and pain in muscle groups. 

brown spider with markings
juvenile and male black widow spiders are brown and smaller than the female

The female Latrodectus spider has extra-large venom glands and her bite is particularly harmful to humans.

In humans and dogs the widow spider bite can produce muscle aches, nausea, and a paralysis of the diaphragm that can make breathing difficult.  Most people bitten do not suffer serious damage or death.  A black widow spider bite can be fatal to small children, the sick and elderly.

Is the black widow spider bite fatal to dogs?  This is a big concern for me as I have two beloved dogs running about the yard.  This harmful spider bite to a dog is basically the same as it is to us humans.

Young dogs, older and those dogs with weaker immune systems are at higher risk for complications from a black widow spider bite.   ****Anti-venom drugs are available but need to be administered by your veterinarian.

Fortunately,  widow spiders are non-aggressive and bite only in self-defense.

poisonous spiders
spiders with large abdomens

Symptoms of a poisonous widow spider bite –

Once the spider’s poison reaches the blood, the venom is moved by circulation, causing its toxins to be deposited in the ends of the nerves that are inserted into the muscle.

The widow spider’s venom acts at nerve endings to prevent relaxation of muscles, causing seizures  —  constant, and painful muscle contractions.

Cramping in the stomach is often the most severe symptom but leg and back muscles may be affected also.

What to do after being bit by a widow spider?  SEEK medical attention after a poisonous spider bite.  Poison Control Website  or American Association of Poison Control  –  1-800-222-1222

Pictured below is the size difference between a male and female widow, Latrodectus, spider.

female widow spider is larger
size of male, female widow spiders, Latrodectus

Most people will recognize widow spiders by the hourglass markings on the underside of their abdomens. The hourglass mark is NOT present in ALL Latrodectus species.

The young female spider is more of a brown color with yellowish, white stripes across the top abdomen that change into the red hourglass shape as she ages and darkens to her black spider color.

most poisonous spiders
juvenile female black widow spider with white and yellow marks

The male widow spider is much smaller in size with brown coloring, and lacks the red hourglass mark the female is recognized for.

black widow before she turns black
young widow spider with yellow-orange marks on abdomen
spider white yellow marks
Latrodectus, widow spider with yellow marks, red dots on large abdomen

One way to rid yourself of a black widow spider is spray the web!  Wear protective gloves and spray the web well.  Spiders consume their old webs before they spin a new one.  Be careful always!

Latrodectus genus of spider, in the family Theridiidae
hourglass marking is common for poisonous widow spiders
dangerous harmful widow spiders
poisonous spider with white and yellow marks

In arid parts of Arizona, Latrodectus spiders inhabit almost every crevice in the soil and nests can be found in cholla cacti and agave plants.

Black Widow Spiders like undisturbed areas.  Keeping your home clean and vacuumed can help prevent these dangerous spiders from taking up residence in your house.


Author: tjsgarden

We are a family that loves the Arizona Desert. A lot of research and team efforts go into our articles and photos. Come discover the beauty and mystery with us. Don't forget your sunscreen!

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