Brown Recluse vs Black Widow: A Detailed Comparison of Two Venomous Spiders

Spiders and insects belong to the phylum Arthropoda and have similar characteristics, including segmented appendages (legs), segmented bodies that are divided into two or three fairly distinct regions, and hard exoskeletons. Although similarities exist, these arthropods are not in the same group or class. Insects are in the class Insecta, and spiders are in the class Arachnida.

There are a number of criteria used to place spiders and insects in separate groups. However, the most obvious rule is the number of legs. Insects have three pairs of legs, and spiders have four pairs. Spiders also have only two body segments, the cephlothorax (combination of head and thorax) and the abdomen, while insects have three segments—head, thorax, and abdomen. Spiders are found in a variety of habitats where they catch and eat many small animals, with insects making up the major portion of their diets.

If you mention spiders, people might have several initial thoughts and reactions. Some might think of the large circular webs they see during the summer and fall seasons. However, some spiders never build a web and use speed (wolf spiders) or stealth (crab spiders) to catch their prey.

Other people may think of the venomous nature of spiders. While it is true that all spiders have jaws, called chelicera, and venom glands, the vast majority of spiders do not have venom that is toxic to humans. Two spiders capable of injecting toxic venom are the brown recluse and the black widow. This publication deals with the biology and control of these two spiders around homes and landscapes in Mississippi.

Control of Black Widow Spiders

Spot Treatment: Eliminating individual black widow spiders as they are discovered, either by crushing them or by spraying with an appropriate contact insecticide (see Table 1), is one of the most practical ways to control black widows. Occasionally, you may encounter a web teeming with hundreds of newly hatched spiderlings, and you will have to use a spray to control these spiderlings because they are too small and too numerous to control by crushing. Also, be sure to check for egg sacs and eliminate these.

Black widow populations are cyclic. Some years, populations are so low that black widows are rarely encountered, but, in outbreak years, there may be dozens of nesting females in a single backyard. Heavy populations often occur in enclosed crawl spaces under buildings. It is rarely necessary or practical to apply broadcast insecticide treatments to an entire yard or area to control black widows.

Habitat Reduction: The key to managing black widow spider populations is to learn to recognize the types of areas where they like to build their webs, and to eliminate these situations as much as possible. Black widow spiders normally nest in dark, protected sites located at or near ground level. This includes stacks of lumber, bricks, concrete blocks, flower pots, or similar materials; piles of wood, tree limbs, or other debris; water meters, electrical boxes, or similar places; crawl spaces under buildings or steps; and bushy, low-growing plants. Sometimes black widows are found nesting in more exposed areas, such as under eaves of buildings, but this is rather uncommon.

Proactively reducing suitable black widow nesting sites is the most effective thing you can do to help reduce black widow populations around your house. Be sure to wear gloves and long-sleeved shirts when removing and handling such items. Most bites occur when people unknowingly press a spider against their skin or place an ungloved hand into the web of a female guarding her egg sac. Habitat reduction is especially important in play yards and other areas frequented by very young children. Inspect play yards regularly, giving special attention to areas where black widows may build their webs.

Awareness and Education: Black widows build three-dimensional webs that have no distinct pattern (not wheel-shaped, etc.), are usually in a dark, secluded place near the ground, and are made of unusually strong silk. Being able to recognize black widow webs, the spiders themselves, their egg cases, and the places where black widows usually nest helps reduce your chances of being bitten. Teach young children how to recognize and avoid black widows and the kinds of places they are likely to occur. Wear gloves and other appropriate protective clothing when working in areas where you might encounter black widows.

Control of Brown Recluse Spiders

Brown recluse spiders are common throughout the state. Low numbers occur in most homes and buildings, but some homes and buildings have unusually heavy infestations. Heavily infested buildings are usually older buildings, buildings constructed in such a way that they contain large numbers of cracks and crevices where spiders can hide, or buildings with large amounts of stored items. Most infestations are likely introduced into a building when brown recluses are unknowingly transported from an infested building in a box of stored items, a piece of used furniture, a piece of electronic equipment, or similar items.

Brown recluse spiders prefer to nest indoors in dark, undisturbed areas. This includes areas such as closets and storage cabinets; under beds; in and under furniture; in boxes; in and behind bookshelves; behind pictures and other wall hangings; in light fixtures and behind wall plates for electrical switches and outlets; in wall, floor, and ceiling voids; and in other dark cracks and crevices. Keeping such areas clean and well-organized helps discourage spiders. Storing items—especially cloth items—in insect-tight plastic containers (rather than cardboard boxes) is especially helpful.

Brown recluses will also inhabit attics and other areas of the home that are not heated and cooled. In many cases, spiders tend to move into attics in the fall of the year as temperatures cool, but, during the summer, Mississippi attics often reach temperatures that are inhospitable to spiders. Owners of infested homes may notice an increase in brown recluse activity in the living areas in late spring as warming temperatures cause spiders to move out of attics and similar locations.

Cleaning and Decluttering: Systematic cleaning and decluttering is the most important step in attempting to control heavy infestations of brown recluse spiders. This means going through each room, closet, and storage area in a systematic manner to declutter, clean, and apply insecticides where appropriate.

Note that cleaning and decluttering is actually more important than spraying an insecticide when attempting to control brown recluse spiders. The basic plan is to remove all items from the area, checking them for spiders as you do so; clean/vacuum all corners, cracks, crevices, and other potential refuge areas; treat the appropriate areas of the empty room or storage area; treat the backs, bottoms, and other appropriate crevices of furniture; allow sprays to dry; and then return items to the room.

The following list gives a general outline of how to approach treating a room or storage area for a heavy brown recluse infestation. This is a lot of work, but it takes a lot of work to do a thorough brown recluse treatment. You can do less, but you will get less control. Many homeowners are reluctant to go to the amount of effort it takes to do a thorough brown recluse treatment—until a family member gets bitten.

If you are finding several brown recluse spiders a month and are sure of their identification, then you definitely have a heavy infestation that justifies the effort necessary to control such an infestation—before someone gets bitten. A thorough, properly conducted treatment effort will result in greatly reduced spider populations, which reduces the chances of someone being bitten. Although spider populations will gradually rebuild, benefits of such an intensive control effort can last for many months.

Spider Bites: Black Widow vs. Brown Recluse

FAQ

What’s worse, a brown recluse or a black widow?

• Venom:

  Brown recluse venom is toxic to tissues and cells, potentially causing skin necrosis (tissue death). 

• Bite Symptoms:

  Bites may initially be painless or cause mild stinging, but can develop into severe pain, swelling, and blistering. 

• Medical Attention:

  Seek medical attention immediately if you suspect a brown recluse bite, as the venom can cause significant tissue damage. 

• Necrosis:

  A brown recluse bite can cause skin necrosis, a process where the tissue around the bite dies and sloughs away, potentially leading to a large, ulcerated wound. 

• Systemic Effects:

  In rare cases, brown recluse venom can cause systemic effects, such as fever, chills, rash, nausea, and vomiting. 

Should I go to the ER for a black widow bite?

• Black widow bites can be dangerous:

  While not always fatal, black widow venom can cause serious symptoms like intense pain, muscle spasms, and difficulty breathing. 

• Seek medical care:

  If you suspect a black widow bite, go to the nearest emergency room or call 911 for immediate medical transport. 

• Symptoms to watch for:

  • Intense pain: The pain can be severe and may spread from the bite site. 

  • Muscle spasms: These can be widespread and very painful. 

  • Other symptoms: Chills, fever, nausea, vomiting, sweating, headache, and in some cases, seizures. 

• Treatment:

  Medical professionals can administer antivenom, which is a medication that neutralizes the venom, and other treatments to manage symptoms. 

• First aid:

  While waiting for medical help:

  • Clean the area: Wash the bite area with soap and water. 

  • Apply ice: Wrap ice in a clean cloth and apply it to the bite area for 10 minutes, then off for 10 minutes. 

  • Keep the area still: Try to keep the affected area still to prevent the venom from spreading. 

  • Loosen clothing and remove jewelry: This is important if swelling occurs. 

• Do not:

  • Apply a tourniquet: This can worsen the situation. 

  • Cut or try to suck the venom out: These methods are not effective and can cause more harm. 

How do you tell the difference between a black widow bite and a brown recluse bite?

• Symptoms:

  • Rapid onset: Symptoms, including muscle cramps and spasms, nausea, vomiting, sweating, and difficulty breathing, can occur within minutes to a few hours. 

  • Systemic effects: The venom affects the nervous system, causing muscle spasms, rigidity, and potentially seizures. 

  • Pain: Initial bite may feel like a pinprick, followed by intense pain and muscle cramps. 

  • Other symptoms: include chills, fever, headache, and restlessness. 

  • Appearance: The bite site may show minor swelling, redness, and a target-shaped lesion. 

• Treatment:

  Local wound care, tetanus prophylaxis, and supportive care, including analgesics and benzodiazepines for muscle spasms. Antivenom is available but has limited availability. 

• Spider:

  Black widows are shiny black with a red hourglass marking on their abdomen. 

What is the most venomous spider in the United States?

• Appearance:

  Brown recluse spiders are small, with a brown color and a distinctive violin-shaped marking on their upper thorax (the area between the head and abdomen). 

• Distribution:

  They are native to the central, southern, and midwestern states of the USA, but have also extended their range into parts of the northern United States. 

• Venom:

  The venom of the brown recluse spider can cause tissue necrosis (death of tissue) and a large, open sore. 

• Bite:

  Bites are often painless initially, but can later cause a stinging sensation with localized pain. 

• Medical Attention:

  A small white blister usually develops at the site of the bite, and the skin lesion will require professional medical attention. 

• Other Spiders:

  While the brown recluse is considered the most venomous, other spiders like the black widow and hobo spider are also dangerous and should be avoided. 

• Black Widow:

  Black widows are known for their neurotoxic venom, which can cause muscle spasms and other symptoms. 

• Hobo Spider:

  Hobo spiders are often mistaken for the common brown house spider, but their funnel web can help in identification.