Holmes Lawn & Pest Blog

The Black Widow Spider

Black Widow Appearance

The black widow is the most dangerous spider in Utah. Found all over the United States, widow spiders can come in several different forms. The species of widow spider most commonly found in Utah is Latrodectus hesperus, or western black widow. The western black widow is part of the Theridiidae, or cobweb spider, family. This family includes over 3,000 different species, only a few of which are considered “true widow spiders.” Western black widows, as well as the other true widow species, are all extremely venomous, and their bites have the potential to cause fatal injuries. Many other cobweb spiders are known as false widows because of their similar appearance to true widows, which is why being able to identify a true widow is crucial. Understanding as much as possible about the western black widow in Utah is of the utmost importance, as this knowledge could potentially save your life.  


Both female and male widow spiders have different colors and markings when they are in immature stages of development. They will both be a lighter color, with orange, red, or yellow markings on their abdominal area that could either be in round or striped formations. As the female gets older, it will begin to take on the shiny black color it is known for, and the famous red hourglass shape will develop as she becomes fully mature. Mature males will have slender bodies that are only half the size of mature female bodies, and they will maintain their lighter brownish color throughout their short lives. Though adult males are not medically significant, their presence greatly increases the likelihood of encountering the dangerous females. 


Adult females are the common image people think of when it comes to black widows. Their bodies can reach about ⅓ of an inch in length, with plump abdominal areas. The western black widow will often, but not always, be all black except for the red hourglass shape on its undercarriage. The hourglass shape is a reliable indicator of a true widow spider, but the shape can vary on a western black widow. Occasionally, the hourglass shape will appear more like two unconnected markings, or the red color may fade and become difficult to see. False widow spiders will lack the hourglass shape, and they will likely be a lighter color as compared to the dark black of a true black widow. Never take any chances if you have been bitten by a spider that at all resembles a black widow. Always seek medical attention!


Webs of black widows are unpredictable and often look messy or erratic. There is no discernible pattern found in black widow webs. It is speculated that the unique structure of a black widow’s web is related to the mating process and how the spiders use the vibrations of the web to communicate. These webs are often found in dark, quiet, and isolated locations in nature and in places like garages or basements. If you think you see one of these asymmetrical and messy webs, stay away from it and consider seeking professional help to identify it.

Life Cycle

A western black widow begins its life cycle in an egg sac that contains hundreds of eggs. The sacs are usually a yellowish color and are attached to the nest of the mother spider, which she will aggressively defend until the eggs hatch. The eggs of western black widows hatch roughly two weeks after they are laid. The new spiderlings will remain in the egg sac while they go through their first molt. Widow spiders are cannibalistic, especially in these early stages of life. Though hundreds of eggs may be hatched in the sac, the majority of them will die and/or be cannibalized by their siblings. The mother spider will occasionally eat her offspring for sustenance, but it has also been theorized that a mother widow spider will eat the larger or more aggressive spiderlings in order to prevent them from killing all the other spiderlings. 


After molting, the surviving spiderlings often leave the sac via a process called “ballooning.” This process involves the spiderlings releasing tiny strands of silk that catch air currents, which carries them away from the sac like a hot air balloon. Once they are on their own, western black widows will begin finding suitable places to build their own webs in order to catch their prey. Molting will continue as the spider matures, with the female fully maturing by six months and the male maturing even faster due to it having less developmental stages than the female. The male will only live for a few weeks or months, but the female can live up to three years given optimal conditions, such as plentiful food, protection from the cold, etc.; however, the average lifespan of a female western black widow is only about one year.

Mating Habits

When it comes to understanding the terrifying reputation of this spider, you do not need to look any further than the name, “black widow.” This moniker is derived from the idea that female widow spiders always cannibalize the males after mating. While this is an observable habit of black widow spiders, males often get through the process without being harmed.


The courtship begins when the male approaches the female’s web and taps on it with its legs. The tapping performed is a type of “dance” that sends vibrations through the web that are then felt by the female. If the female is receptive, she will also tap the web in response. The vibrations created during this ritual are unique to each species of widow spider. After receiving the vibrations back from the female, the male will cautiously approach the female and lightly touch her with his legs. If the female allows the touching, mating will begin. 


As the male performs his tapping and approaches the female, the female may attack if she is not receptive or if she is simply hungry. However, a healthy male that is proceeding with caution is usually able to evade the attack. If the female is well fed, the likelihood of her cannibalizing the male after mating drastically decreases. Of course, if the female is hungry and needs the extra nutrients for her eggs, she may consume her mate after copulation.

How Dangerous Are They?

Western black widow spiders do not always inject venom when they bite. In fact, a venomous bite usually only occurs when the spider is physically touched and feels its life is in danger. A non-venomous bite will sting the flesh and become irritating, but it is not likely to cause any significant harm. However, when the black widow does inject venom as it bites, most reports suggest that the initial feeling is much more intense and painful. 


True widow spiders produce a neurotoxin that affects muscle function and the nervous system. In severe cases, an intense burning sensation may be felt by the victim, followed by pains in the chest and abdomen. Other symptoms may include excessive sweating, fever, and nausea. In rare cases, victims may experience hallucinations, muscle spasms, and swelling of their extremities. The most extreme result of a black widow spider bite is death, but this is highly uncommon, especially if medical attention is immediately sought. Symptoms most often last from days to weeks, with varying levels of severity and duration. 


There are easy steps to take in order to avoid being bitten by a western black widow spider in Utah. Thankfully, black widows do not want to be disturbed and rarely venture far away from their webs. Under natural debris or between bushes that are not often touched by people are the kinds of places black widows can be found in nature. When found indoors, these spiders are usually in areas of basements or garages that are dark and undisturbed. So, when you are taking care of spring cleaning or rummaging around dark corners for some long-forgotten item, never reach blindly with uncovered hands. To protect yourself against western black widows, always wear thick gloves when performing tasks in these areas, and always look at where you are placing your hands. Being mindful of your surroundings is the best way to avoid a black widow, but, if you do find one, call in the experts at Holmes Lawn & Pest!


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