Spiders -- Brown Recluse & Black Widow

Printable PDf Version (6 pages)

Introduction

Spiders and insects belong to the phylum Arthropoda and have similar characteristics, including segment appendages, i.e., legs, a segmented body that is divided into two or three more or less distinct regions, and a hard exoskeleton. Although similarities exist, they are not in the same group or class. Insects are in the class Insecta, and spiders are in the class Arachnida.

A number of criteria are 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, whereas 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.

Mention spiders and people might have several initial thoughts and reactions. Some might think of the large circular webs that are evident through 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. Some people will think of the venomous nature of spiders. While it is true all spiders have jaws, called chelicera, and venom glands, the vast majority of spiders do not have a venom that is toxic to humans. Two spiders capable of injecting a toxic venom are the brown recluse and the black widow. This publication will deal with the biology and control of these two spiders around homes and landscapes in Mississippi.

Brown Recluse (Loxosceles reclusa)

Description

The body of this spider, excluding the legs, is between 3/8 of an inch (9.5 mm) and 1/2 of an inch long (12.7 mm) and 3/16 of an inch (5 mm) wide. The legs are long and slender, making the body appear larger than its actual size. Coloration is variable, but generally it is brown to yellowish brown, with the abdomen darker than the cephlothorax.

The main identifying mark found on the recluse is the “fiddle-shaped” structure located on the front of the cephlothorax. The wider part of the fiddle is near the head, with the bow or handle starting about the middle of the cephlothorax and running toward the abdomen. The fiddle is darker than the surrounding body and stands out against the lighter background.

The body of the spider appears slick or void of hair, but when viewed under magnification, it is covered with small, brown hairs. This covering of hair gives the abdomen a somewhat velvety appearance. The number of eyes of a brown recluse is diagnostic. The recluse and its relatives have six eyes, compared to eight for most other spiders.

Habitat

The brown recluse is found statewide in Mississippi and is typically thought of as an “indoor” spider, but populations do exist in outdoor situations. For example, University of Arkansas researchers kept site-collection data on brown recluse spiders from May 5, 1962, through December 31, 1964. A total of 626 spiders were collected during this period, and 196 spiders, or 31 percent, were collected from outside locations. The predominant outdoor site was under large, flat rocks in the rocky bluff habitat of north to northwest Arkansas. Other outdoor collections came from under bark and from around debris piles. With the exception of northeast Mississippi, the rocky bluff habitat does not exist within the state. However, the other habitats do exist and would provide areas of survival for the spiders in natural settings.

Although the brown recluse spider can be found outside, most are found in structures of various types. Of the 626 spiders reported, 298 spiders (47 percent) were collected from homes, 74 spiders (12 percent) came from schools, and a miscellaneous building category showed a total of 58 spiders (9 percent). In buildings, the spiders were found in places that included boxes, stacks of papers, attics, old shoes, little-used clothing, closets, under furniture, behind picture frames, and window wells and cabinets. Most evidence would support a dry, dark, undisturbed area as the habitat of choice for this spider. There are times, however, when brown recluse spiders are found crawling about in the middle of a well-lit room with ongoing activities. This behavior does not fit the expected norm for the spider and, at the present time, there is not an explanation for its presence under these circumstances.

The brown recluse spins a rather nondescript web with threads that run in all directions. When fresh, the web is whitish in color, but with time, it collects dust and becomes an off-white or grayish-white color. This structure is used as a resting site, retreat, or as a nursery—it is not used to catch prey.

Biology

Laboratory data show that the recluse is a fairly long-lived animal. According to the data, 32 males lived an average of 543 days, and 20 females lived an average of 628 days. This may not be the norm for spiders existing in nature or even in a somewhat protected structure, but it does point to a possible life span of 13 to 18 months.

There are three stages in the growth of the recluse. These stages are egg, immature (spiderling) with eight stages, and adult. The eggs are not laid individually but are placed in a sac with each sac containing an average of 50 eggs. A female produces from one to five sacs over her life span, with the majority of the egg cases produced during May, June, July, and August. The sacs have not been recorded during the months of October, November, December, and January. It takes an average of 336 days to go from egg to an adult spider (range 266 to 444 days).

Venom

With the brown recluse spider, the male and female are capable of biting and injecting a necrotic poison into the victim. Reaction to the bite depends on a number of factors, including skin thickness at the point of the bite, amount of venom injected, individual sensitivity, and time from the last bite to the present bite.

The bite itself is apparently not painful to most victims, since the victims often report they were not aware of when the bite occurred. The symptoms associated with the bite can vary from person to person, and the following description may not fit every case of brown recluse bite.

The first symptoms occur 2 to 6 hours after the bite. These symptoms are an itching and swelling and redness at the puncture site. A small whitish area will encompass the reddened area. A small pimple-like structure will form soon after, followed by a blister. As the envenomation process progresses, the wound site becomes bluish or purplish due to a restricted blood flow and/or a destruction of red blood cells. At some point in the process, a black scab- similar to a burned area may form; this falls off in about 2 weeks to reveal an ulcerated wound. Healing is slow, and it may take 6 to 8 weeks or longer for the wound to heal.

The sooner treatment is begun the better; however, there is not total agreement on the treatment regimen. Past treatments have included antibiotics and corticosteriods to treat infection and relieve inflammation, and surgical removal of damaged tissue. In some cases, dapsone has been used to treat these lesions. Whatever the case, persons with bites or suspected bites should be under the care of a physician.

Black Widow (Latrodectus mactans)

Description

There are five spiders in the “widow” group. Two are restricted to southern Florida, and one is found in the western parts of the United States and Canada. The one most often referred to as “the black widow spider” is the species L. mactans found in the Southern states. The last widow spider is the “northern widow” found across the northern United States and into New England.

The female of the black widow is the one most often seen. It is a characteristic shiny black color with a red hourglass mark on the underside of the abdomen. Occasionally, there are red dots or hash marks on the upper side of the abdomen as well. The body, excluding legs, is 7/16 of an inch long (11 mm) and 5/16 of an inch (7.9 mm) to 3/8 of an inch (9.5 mm) wide. With a distinct globular shape, the abdomen is larger than the cephlothorax. The first and fourth pairs of legs are long and slender, which adds to the overall perception of size. Black widow males (not reported to have caused any venomous bites) are considerably smaller than the female black widow, and its abdomen is more elongate rather than the globular shape of the female.

Habitat

This spider is found almost exclusively in outside habitats. It can be found in the crawl spaces of houses, in water meter boxes, under rocks, in stumps or logs, around refuse piles, in brick piles, and in stacks of firewood. If spiders use buildings, they tend to be old abandoned barns, houses, sheds, or the little-used sections of garages or basements. Spider populations, in general, will fluctuate with high and low years; however, with the black widow, high populations in a given area are rare. The controlling factor may be disease, predators, lack of suitable habitat, and/or competition, along with some degree of cannibalism among the spiders.

The web is an indistinct mesh of webbing in which the spider hangs with head pointed down. In this case, the web is used to snare prey that ventures into the area. If the web is built in a somewhat open area, the spider might be under a nearby dirt clod, rock, or piece of debris during the day, since they will avoid light. The black widow returns to the web at night and waits for an insect or other arthropod to become stuck in the web.

Biology

The black widow has three growth stages—egg, immature (spiderling) with 7 to 9 stages, and the adult spider. The spider spends the winter as a late-stage immature or an adult in a protected site. In the spring the spiders become active, and the males seek out and mate with mature females. Soon after mating, females start producing egg sacs and will produce three to six during the spring and early summer. Each sac will contain an average of 255 eggs. These females probably die by the end of summer or early fall. Young spiders will disperse from the nest site by ballooning, which is accomplished by crawling up grass blades, stems, or other upright objects on windy days and extruding strands of silk from their silk glands. As the wind catches these strands, the young spiders are lifted into the air and deposited at some distant point. Once in this area, they seek out a suitable site for web construction.

Venom

The bite of this spider, as with the brown recluse, often goes unnoticed. The chelicera are only about one millimeter in length, and they may have trouble breaking the skin at some points on the body. The amount of venom injected, the age of the victim, and the elapse time from the last bite until the present bite are some factors that determine the severity of symptoms experienced by the victim. Shortly after the bite (30 to 45 minutes), the skin around the puncture site might become red with a central white or blanched area. A close examination might reveal the two puncture points. The venom is neurotoxin (acts on the nervous system) and, as the envenomation process progresses, pain increases and a contraction or cramping might be noted in the thighs, lumbar region, abdomen, or chest area. This muscle cramping or rigidity is particularly severe in the abdominal muscles. Muscle cramps will make walking difficult in some patients, and a slurring of speech is often noted.

Black-widow-bite treatments might include the use of an antivenin given intramuscularly for 1 or 2 days, plus pain management using calcium gluconate. If two doses of calcium fail to relieve pain, morphine sulfate may be used. These treatments must be prescribed by a physician. Warm baths may help relieve muscle spasms.

Controls

for the Black Widow and Brown Recluse

Management practices for these spiders vary, depending on the infested site and the numbers of spiders that might exist within or around the site. For example, black widows seldom, if ever, occur within occupied dwellings to the same degree as the recluse. In this case, recluse management practices would be more extensive due to the greater number of spiders that might exist in the home. Conversely one spider, black widow or brown recluse, seen around brick or other refuse piles would not necessarily need the same attention.

Outdoor Controls

Habitat management in outdoor areas is the primary control practice you should follow. This includes any practice that eliminates sites used for protection, web building, or hunting. It includes the removal of excess bricks, racks of old firewood, sheets of tin or lumber stacked on the ground, dense plant growth, or similar habitat. When cleaning these areas, wear gloves to protect hands against any accidental contact with the black widow or recluse. Be cautious when removing water meter covers, or opening outside electrical boxes, since the dark nature of these areas is ideal black widow habitat.

Storage Buildings

Various buildings might be used for temporary storage and are rarely entered, except to retrieve or store an item. Take care when working around or entering these areas. When items such as tents, out-of-season clothing, sleeping bags, shoes, or tarpaulins are removed, carefully inspect items before use. To prevent spider problems in these areas, place items for storage in tightly sealed boxes or other containers, elevate items from the floor, remove unwanted items, and periodically clean by sweeping or vacuuming. After cleaning, insecticides can be applied to cracks and crevices around and in the building.

Homes

The brown recluse is the major venomous spider known to occur within homes, and controls can be difficult. Insects, such as cockroaches, follow a fairly predictable pattern of movement within the building, and it’s easy to take advantage of this when applying an insecticide. The brown recluse, however, moves erratically within the home and it is not practical nor advisable to treat every surface over which the spider might crawl. Finally, control is complicated by the secretive behavior of the spider. It tends to seek out dark, undisturbed areas, and it might be difficult to identify all such sites. Spider control can be accomplished by hiring a professional pest control service or as a do-it-yourself project. Whichever choice is made, the first step is to make a thorough inspection of the structure.

Inspection

The inspection helps define the areas that might harbor spiders. Inspection should include all rooms, closets, cabinets, under furniture, behind furniture, behind picture frames, and the attic. During the summer, attic temperatures can approach 150 °F; however, spiders have been found in home attics. The spiders probably forage for food during the cooler parts of the night and early morning. As the temperatures increase, they possibly seek shelter in boxes, under insulation, or in other protected sites. During the inspection process, look for live spiders, cast skins, egg cases, or webbing. Some of this might be hard to identify as related to the brown recluse, but it can be important. If areas (attics or closets) are not accessible due to stored items, it is advisable to sort through and discard unwanted items in order to make inspections and any eventual treatments easier.

Another component of the inspection process is the use of sticky traps. These are small box- or tent-shaped structures open on both ends with an inside sticky surface. They can be placed at various locations within a room and checked periodically for spiders.

Professional Pest Control Service

These organizations have trained personnel and special equipment (sprayers, dusters, aerosol generators) to administer different applications for pest control. They also have the added advantage of being able to use insecticide formulations (Table 1) that are not available to the general public. These formulations are dusts (D), wettable powders (WP), drying agents (DA,) such as silica gel, and micro-encapsulated (MEC) materials. Some limited evidence indicates that WP and MEC formulations may give better spider control than other formulations, i.e., emulsifiable concentrates. Resmethrin, as an aerosol, can also be used by the professional services. Aerosols are released as small particles and are useful in treating attics, wall voids, or crawl spaces. Aerosols will not penetrate into boxes or insulation but will give good short-term control of exposed spiders.

Homeowner Treatment

This is an option if you feel comfortable in this role, and it is cheaper; however, there are a limited number of product formulations available for home use. Products available for home use may be categorized as residual treatments or short-residual treatments.

Residual Treatments

These insecticides are formulated as ready-to-use sprays (RTUs—do not have to mix with water) or aerosols (A), and they give control for a period of weeks, depending on the treated site. Materials available as RTU sprays or A’s are deltamethrin 0.02 percent (Hi-Yield Kill-A-Bug II, RTU), bifenthrin 0.05 percent (Ortho Home Defense Indoor and Outdoor Insect Killer, and Raid Home Insect Killer, RTU’s), as well as a number of RTU’s that contain the active ingredient permethrin. Carefully check the ingredient statement for this active ingredient and make sure the product that is purchased has an indoor-use statement on the label. A number of active ingredients are available in the A formulation. Examples are cyfluthrin 0.1 percent, piperonyl butoxide 0.5 percent, tetramethrin 0.5 percent (Raid Max Roach & Ant Killer III), and permethrin 0.20 percent (Raid Ant & Roach Killer).

Short-Residual Treatments

Products in this category last for less than a day to several days. These materials are available as controlled aerosols or total release aerosols (TRA), often referred to as foggers. The best results with the controlled aerosols are obtained by directing the spray at or into those areas favored by the spider. The TRAs are convenient to use and work well in confined spaces; however, they kill only those spiders in the open at the time of the treatment and give little if any residual control. Ingredients found in these products are allethrin, pyrethrin, pyrethrin plus pipernyl butoxide, tetramethrin, resemethrin, and phenothrin. Some of the total-release aerosols contain permethrin, which will increase the residual effectiveness of this product. If a TRA is used to treat attics during the summer months the treatment should be made in the early morning. When using TRAs, be sure to follow label information relative to pilot lights and electrical motors.

Whether controls are initiated by a professional service or homeowner, the best results will be obtained by placing the product into those areas attractive to the recluse. These areas include cracks and crevices that might lead into wall voids, backs of closets or cabinets, behind and under furniture, in storerooms, and any other little-used area of the structure. Controls are further enhanced by a thorough cleaning and reorganization of storage areas and the discarding of any unwanted items.

If spider control is a do-it-yourself project, read and follow all application, safety, and disposal information on the label of the product or products of choice.

Photography: Black widow and wolf spider photographs from Ross Hutchins Photographic Collection, Mississippi State University; photograph of brown recluse bite on leg courtesy of Jerome Goddard and the Mississippi Department of Health. Spider bite in early stage of necrosis, reprinted from Goddard's Physicians Guide for Arthropods of Medical Importance. 1993. CRC Press, Inc., Boca Raton, FL, courtesy of Dr. Tom Brooks.

By Dr. James H. Jarratt, Extension Entomologist, and Dr. Jerome Goddard, Medical Entomologist, Mississippi Department of Health.

Publication 2154
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Joe H. McGilberry, Director

(rev-1M-6-03)

Copyright by Mississippi State University. All rights reserved.

This document may be copied and distributed for nonprofit educational purposes provided that credit is given to the Mississippi State University Extension Service.