Conditions Basics

What is a black widow spider?

Black widow spiders (Latrodectus mactans and Latrodectus hesperus) are found throughout southern Canada, the United States, and Mexico. A female black widow is much more likely to deliver more venom than a male spider. Female black widows are long-legged, shiny, coal-black spiders with an orange, red, or yellow shape on their underside that usually looks like an hourglass but may be another shape. Female black widows are usually about 3.8 cm (1.5 in.) long, but they may be smaller.

Black widow spiders are frequently found in low-lying webs in garages, in barbecue grills, around swimming pools, and in wood piles. Most bites occur in rural and suburban areas and occur between the months of April and October. These spiders tend to bite defensively when their webs are disturbed. Bites to babies, children, and older adults may be more serious.

What are the symptoms of a black widow spider bite?

In most cases of a black widow spider bite, symptoms consist only of:

• Minimal to sharp pain followed by swelling and redness at the site of the bite.
• One or two small fang marks like tiny red spots.

In some cases, severe symptoms appear within 30 to 60 minutes. These include:

• Muscle cramps and spasms that start near the bite and then spread and increase in severity for 6 to 12 hours.
• Seizures.
• Chills, fever, nausea, or vomiting.
• Sweating.
• Severe belly, back, or chest pain.
• Headache.
• Stupor, restlessness, or shock.
• Severe high blood pressure.

What should you do if you think you've been bitten by a black widow spider?

Follow these steps if you believe you have been bitten by a black widow spider.

• Get medical help immediately.

  Call your doctor, hospital, or local poison control centre.

• Remain calm.

  Too much excitement or movement will increase the flow of venom into the blood.

• Apply ice to the bite area.
• Do not apply a tourniquet.

  It may cause more harm than benefit.

• Try to positively identify the spider or catch it to confirm its type.

How is it diagnosed?

A black widow spider bite is diagnosed through a physical examination and questions about the bite. You should be prepared to describe the spider, where and when the bite took place, and what you were doing at the time. Your doctor will ask what your main symptoms are, when they began, and how they have developed, progressed, or changed since the bite.

How is a black widow spider bite treated?

Medicine to counteract black widow spider venom (antivenom) is available in Canada, the United States, and Mexico. It is usually used if you have trouble breathing, have high blood pressure, or are pregnant. Children and older adults with some medical conditions may also be given the medicine if their symptoms are serious.

Treatment also includes:

• Medicine for pain and spasms. Pain and spasms may be severe enough to require benzodiazepines, such as lorazepam (Ativan) or diazepam (Valium), or opioids, such as morphine or fentanyl. Calcium may also be used.
• Antihypertension medicines for high blood pressure.