Latrodectus

Widow spiders live all over the world.

Most females are black or dark brown. They often have red marks on their bellies. These marks look like an hourglass.

These spiders build messy, sticky webs. They hide in dark places like woodpiles. They wait for bugs to get stuck in the silk. The spiders have very poor eyesight. They feel vibrations in the web to find food. They are not mean spiders. They only bite if they feel scared or squeezed.

Widow spiders are a group of spiders. They are found on every continent except Antarctica.

Most female widows are dark brown or black. They often have red marks on their underside. These marks can look like an hourglass. This shape helps people find them. Males often have red or white spots on their backs.

These spiders have a very strong venom. It contains a toxin called latrotoxin. This toxin can cause muscle pain or cramps. Only female bites are dangerous to humans. Most bites do not cause serious harm. Some bites are "dry," which means no venom is sent.

Widow spiders build messy, sticky webs. They like to hide in dark spots. They may live in woodpiles or under furniture. They have poor eyesight. Instead, they feel vibrations in the web. This tells them when an insect is stuck. They use silk to wrap their prey. Many people think they are mean. But they only bite if they feel scared. They often try to play dead instead.

Widow spiders are a group of spiders known as the genus Latrodectus. There are about 34 or 35 different species in this group. Many people call them black widows or brown widows. These spiders live on almost every continent on Earth. They are found everywhere except for Antarctica.

Some famous types include the southern black widow from North America. There is also the redback spider found in Australia. You might even see the katipo spider in New Zealand. These spiders are important to study because they are quite unique.

These spiders use a special way to catch their food. They build webs made of tangled, sticky silk. The spider often hangs upside down in the center of its web. It waits for a small insect to fly into the silk. Because these spiders have poor eyesight, they feel vibrations. The web tells them when something is stuck. Once the insect is caught, the spider wraps it in silk. Then, it uses digestive juices to turn the insect into a liquid. The spider sucks up this liquid to eat.

Scientists have spent a long time studying these spiders. A man named Charles Athanase Walckenaer created the name Latrodectus in 1805. Later, in 1959, a scientist named Herbert Walter Levi studied them more closely. He looked at the female organs to understand how they were related. He found that many species were actually very similar. In the early 1900s, two other scientists had a big disagreement about them. One scientist even called the other an "ignoramus" during their debate. It shows that even experts can disagree about nature.

Female widow spiders are often dark brown or shiny black. Many have a red or orange hourglass shape on their underside. This shape is called the ventral surface. Males often have different red or white markings on their backs. The venom in these spiders is very strong. It contains a toxin called latrotoxin. This toxin can cause muscle pain or cramps in humans. Only the bites from females are dangerous to people. In the United States, about 2,500 people are bitten each year. However, most people do not need medical help.

It is helpful to know how these spiders act around us. Most widow spiders are not aggressive. They usually only bite if they are startled or squeezed. If they feel trapped, they might try to play dead. They also make very strong silk. The silk of the western black widow is very tough. It is similar to the strength of steel wire. However, silk is much lighter than steel. This makes the spider's web a very effective tool for survival.

The genus *Latrodectus* contains a group of spiders commonly called widow spiders. This group includes famous species like the black widow and the brown widow. These spiders belong to the family Theridiidae. They are found on almost every continent in the world, except for Antarctica.

Scientists study them to understand how potent venom works in nature. They also study them to learn about unique behaviors and silk strength.

Widow spiders use a specific method to capture and eat their prey. They build webs using irregular, tangled, and sticky silken fibers. Because these spiders have very poor eyesight, they rely on vibrations. When an insect hits the web, the spider feels the movement. The spider then rushes to the prey to envenomate it. It wraps the insect in silk to secure it. To eat, the spider pulses digestive juices over the prey. This turns the insect into a liquid slurry. The spider then uses capillary action to suck the liquid into its mouth.

There are approximately 34 to 35 different species within this genus. Many species are identified by their specific colors and markings. Most adult females are dark brown or shiny black. They often have a red or orange hourglass shape on their ventral surface, which is the underside of the abdomen. Some females have red spots instead. Males often show different patterns on their dorsal surface, or upper side. These patterns can include single stripes, bars, or spots.

Juvenile spiders often look more like the males.

Different species live in many different parts of the world. In North America, you can find the southern, western, and northern black widows. The red widow and the brown widow also live there. The brown widow has a very wide geographic distribution. In Australia, the most common species is the redback spider. New Zealand is home to the katipō spider. In South America, species like *Latrodectus corallinus* live in Brazil and Argentina. These variations show how the genus has adapted to many environments.

History shows that scientists have often debated how to classify these spiders. Charles Athanase Walckenaer established the genus *Latrodectus* in 1805. In 1902, two scientists named F. O. Pickard-Cambridge and Friedrich Dahl had a famous disagreement. They criticized each other's work while trying to revise the genus. Later, in 1959, the arachnologist Herbert Walter Levi revised the group again. He studied the female sexual organs to find similarities between species. He discovered that color differences were not enough to create new species names. This helped scientists organize the genus more accurately.

One of the most notable features of *Latrodectus* is its potent venom. The venom contains a neurotoxin called latrotoxin, which is also the name for the condition latrodectism. This toxin can cause severe muscle pain, abdominal cramps, and tachycardia, which is a fast heart rate. Only the bites from females are dangerous to humans because they have unusually large venom glands. In the United States, about 2,500 people report bites each year. However, most do not need medical treatment. A 2012 review found no deaths from black widows in the U.S. since 1983.

Widow spiders also exhibit fascinating and sometimes intense behaviors. The name "widow spider" comes from sexual cannibalism. This is when the female eats the male after they mate. This behavior might help the offspring survive. However, some species rarely do this, and much of the evidence comes from laboratory cages. In the wild, males may sense chemicals in the web to see if a female has already eaten. This helps them avoid being eaten. Some species, like *Latrodectus hesperus*, are called opportunistic cannibals because they may also eat their siblings.

Finally, the physical properties of their silk are quite remarkable. The silk of the western black widow, *Latrodectus hesperus*, is very strong. Scientists have measured its tensile strength at about 1,000 MPa. This strength is comparable to steel wire of the same thickness. However, silk is much lighter than steel. Because steel is about six times denser than silk, silk is actually stronger than steel by weight. This strength helps the spider maintain its web and capture prey effectively.