The World’s Most Poisonous Spiders
While many spiders possess venom, only a few species cause significant harm. The venom is injected during a bite using the mobile fang-like apparatus known as the chelicerae.
Bites from these spiders usually cause pain, swelling, and bleeding at the site of the bite. The more serious symptoms occur when the venom is absorbed into the bloodstream. Click the Poisonous Spiders In Kentucky to learn more.
Black widow spiders, Latrodectus venaticus, are one of the world’s most poisonous spiders. The females are distinguished by a red hourglass-shaped mark on the underside of their abdomen. They are found worldwide in dark, sheltered places such as animal burrows and the bases of rocks, bushes, and woodpiles, where they build sticky webs. These spiders are notorious for biting defensively when their webs are disturbed. Bites to children and elderly adults can be particularly serious.
Symptoms of black widow bites typically begin about 15 minutes after the bite. Initially, the pain is like a pinprick, and minor swelling and a target-shaped sore appear at the bite site. Within about half an hour, muscle cramping and stiffness spread from the bite area to other parts of the body. The neurotoxic venom is especially dangerous to young children and older adults.
The black widow’s venom contains a neurotoxin that blocks nerve cell functions, causing pain and tightness. Normally, the pain is localized, but in severe reactions, it can spread to other parts of the body, such as the chest and abdomen. Eventually, it can cause difficulty breathing.
In addition to the pain, the venom can also cause nausea and sweating. Rarely, rhabdomyolysis and myocarditis can occur with black widow bites, leading to elevated creatine kinase in the blood and a rapid heart rate.
Most victims of black widow bites recover without treatment. The antivenin is available to treat severe reactions but should be given as soon as possible after the bite. Death from a black widow bite is rare but can occur in young children and the elderly.
Black widows produce sticky webs that cling to the skin, and they may also leave small fang marks like tiny red spots. The spiders are not insects, but arachnids with a segmented body and eight jointed legs. They are active at night, and they hunt insects that visit their webs. The black widow’s bite is more dangerous than the bite of a rattlesnake because it causes muscle cramping, stiffness and a painful, spreading muscle spasm.
Brown Recluse
Brown recluse spiders are venomous and use their fangs to subdue and digest their prey. Their venom causes damage to the soft tissues of their victims, including muscle tissue, and in rare cases may cause a deadly necrotic wound known as dermoecrosis.
While bites from other spiders can produce similar wounds, most of them do not result in the necrotic lesions that occur with brown recluses. Brown recluses are well adapted to living in our homes and can be found throughout the country, as well as in woodpiles and other dark, sheltered places outdoors. They are able to adapt to changing weather conditions and can live through the winter.
One valuable method for preventing the spread of the brown recluse is to deny them access to their favorite hiding places. Garages, crawl spaces, attics, wall voids and cracks around fireplaces provide ready harborage. Clutter, boxes, furniture, and stored goods should be eliminated from these areas. Boxes and materials that are stored for long periods of time should be placed in plastic bags or tubs and sealed securely to prevent the entry of brown recluses.
The main identifying characteristic of the brown recluse is a fiddle-shaped marking on the front portion of its body (cephlothorax). This feature, often described as a bow or handle, is darker than the rest of the body and stands out against the lighter background. The body of the brown recluse is hairy and gray-brown, with six eyes arranged in three pairs.
Like all spiders, the brown recluse is a good climber and will hide in holes or crevices when disturbed. It can also jump but is not likely to do so unless provoked.
If you suspect that you have a brown recluse bite, seek medical attention immediately. In addition to examining your wound, the health care provider will also check your vital signs and treat any symptoms that develop. The doctor will probably give you pain medicines and antibiotics if the bite becomes infected. In very rare cases, brown recluse bites can cause systemic loxoscelism, a condition that involves a blood clotting disorder and destruction of red blood cells.
Redback
The redback spider is one of the most venomous in the world. The venom contains a mixture of neurotoxic compounds that disrupt nerve signals resulting in intense pain, nausea and vomiting, increased blood pressure, muscle spasms and even respiratory failure. However, it is extremely rare for people to die from a redback bite. The redback spider’s venom is slow-acting and it takes between 15-30 minutes for the victim to begin experiencing symptoms of envenomation.
Redbacks are easily recognisable due to the prominent red stripe that runs down the back of a female spider’s body. Males of the species are a light brown colour and lack the stripe. Like all members of the Therdiidae family, the redback is a carnivorous predator that feeds on insects and other spiders.
A redback’s web is a complex tangle of silk. The rear portion forms a funnel-like retreat area where the spider holds its egg sacs and prey items. A vertical silk strand running down to the ground catches insects and acts as a trip wire to alert the spider when prey approaches. Another strand tethers the prey item or catapults it upward into the web to be eaten.
Like other spiders, the redback ingests its prey by inserting its fangs into it. The bite of a redback is painful and may cause localised swelling. However, because the venom is slow-acting, symptoms such as sweating, itching, nausea and vomiting develop much later. In the majority of cases, a simple ice pack is enough to alleviate symptoms, and only around 6% of bite victims require antivenin.
Bites by a redback often occur when a person inadvertently disturbs the spider’s hidden dwelling. As these spiders build their webs in sheltered, dark places it’s important to always check before reaching into walls and roof cavities, sheds and garages. In addition, make sure that you shake out clothes, shoes, gloves and garden tools that have been left outside before use.
The venom of the redback contains several different neurotoxins, but it is the alpha-latrotoxin that is most responsible for human reactions. Alpha-latrotoxin releases a number of neurotransmitters that inhibit the release of other neurotransmitters and, as a result, prevents the body from receiving the necessary amount of oxygen.
Yellow Sac
The Yellow Sac is a solitary spider that earns its name by constructing small silk “sacs” in which to rest during the day. Like other arachnids, it is a nighttime hunter that carries out its prey in the dark. As such, it may accidentally crawl onto people who are sitting on a sofa or lying in bed and bite them. The venom from this spider does not have the long-term side effects of more dangerous arachnids, but it does cause pain and swelling.
While this spider is most often found outdoors, it can access human dwellings through open doors and windows. Once inside, it hides in secluded areas such as basements and attics. Unlike Black Widows or Brown Recluses, it does not spin webs in these locations, but instead relies on its agility and stealth to ambush insects that venture too close.
During the fall, immature Yellow Sac Spiders migrate inside homes to escape the cold. They seek warmth, and as they move around, they construct webbed retreats in corners of rooms, behind furniture, and in cluttered storage spaces. Typically, they are not seen in gardens or outdoor yards, but their presence inside the home may indicate high insect populations in the yard.
As the weather cools, these spiders will emerge and seek food, primarily other insects. They are active hunters, using their excellent vision and agility to ambush unsuspecting prey. They do not wait in webs, but rather go out looking for food at night.
While these spiders do not spin elaborate webs, they do create silken retreats in crevices and protected areas of landscaped gardens, in which to rest during the day. These retreats are also used for hunting, providing a place to ambush passing insects.
Like most spiders, Yellow Sacs are carnivorous and will eat both live and dead insects. While this spider does not eat fruit, it may occasionally consume nectar in order to feed its young.
Insecticide treatments that contain bifenthrin will provide effective control of this pest, but removing possible harborage areas is equally important. For example, repairing caulking around windows and replacing weather stripping on doors will prevent Yellow Sac Spiders from entering the home. Also, removing debris and clutter from outside the house will eliminate places where these spiders can hide until feeding time.