Archive for the ‘iNSCENtS’ Category
ï»¿Scientific name: Latrodectus hesperus
Country: United States
Continent: North America
Diet: Insects: insectivore, also small reptiles, small mammals
Food & feeding: Carnivore
Habitats: Urban, temperate forest & woodland, temperate grassland
Conservation status: Not threatened
Relatives: Red-back spider
Species: United States: Red widow, Latrodectus bishopi; Brown widow, L. geometricus; Western black widow, L. hesperus; Southern black widow, L. mactans, and Northern black widow, L. variolus
Size:Adult females have a body length (cephalothorax and abdomen combined) of approximately 1/2 inch (~1.25 cm) and a total leg span of approximately 1-1/2 inches (~4 cm) (Figure 2). However, there is much variation in female size, particularly gravid (egg-carrying) females. The abdomen of a gravid female can be greater than 1/2 inch (~1.25 cm) in diameter.
Males are much smaller, often having a body length less than 1/4 inch (< 0.75 cm) and a leg span of approximately 1/2 inch (~1.25 cm).
The black widow spider gets its name from the popular belief that the females eat the males after mating. In fact, this is a phenomenon which rarely occurs in nature. The males’ venom sacs cease to develop at an early age, as they do not feed during adulthood and instead spend their time searching for mates. The females, on the other hand, are one of the most venomous spiders, although their bites are not usually fatal for humans because they inject only a small amount of venom. Females are easily recognised by their shiny black body with a red hourglass marking on the underside of the abdomen. Their bodies are about 8-10 mm long. The males are half the size of the females, with smaller bodies and longer legs. They usually have markings on their backs, as do the immature stages.
Like all spiders, the widow spiders have two main body parts, the cephalothorax and abdomen. The cephalothorax bears the head and legs. The abdomen is much larger than the cephalothorax. The spinnerets, or silk and web making appendages, are attached to the rear end of the abdomen. On widow spiders, the spinnerets look like a cluster of small cones.
The web of widow spiders is not the orderly, geometric web of the orb weavers and many other spiders, but a tangled mass or cobweb. The widow spider typically lives in a small retreat in one portion of the cobweb and detects vibrations from insects that get trapped in the web.
There are five different species of widow spider found in the United States: the red widow (L. bishopi), the brown widow (L. geometricus), the Western widow (L. hesperus), the Southern widow (L. mactans), and the Northern widow (L. variolus). The Western widow is found mainly west of the Mississippi. The red and brown widows are found mainly in Florida, but the brown widow has been found as far west as Texas. In Virginia, the Northern and Southern black widows are the species typically found.
Females of the Western, Southern, and Northern widows look like the classic black widow spider . The body is shiny black and the underside of the abdomen has orange-red marking(s) on it. The Western and Southern widows usually have the distinctive red hourglass on the underside of the abdomen although it is important to note that the hourglass is sometimes separated into two triangular parts. The Northern widow almost always lacks a complete hourglass and instead has two red bars on the underside of the abdomen and red bars on the top of the abdomen. Many female widows will also have an orange-red spot immediately above the spinnerets on the top of the abdomen .
The Red widow female has a reddish colored cephalothorax and a dark reddish brown to black abdomen. The underside of the abdomen may bear the red hourglass or there may just be a non-distinctive red mark. The top of the abdomen is spotted with orange and yellow.
The Brown widow female varies in color from light brown to dark grey and the hourglass on the underside of the abdomen typically is more orange than red. Lighter colored females may have whitish spots along the upper sides of the abdomen, similar to the marking of immature widow spiders.
Male widows may be either completely black or maintain some of the immature coloration. They do not possess the hourglass type marking of the larger females. However, males usually have some red marking located on the top or underside of the abdomen.
The coloration of the juvenile widow spider typically is quite different from the adult. The abdomen is grayish to black with white stripes running across it and spotted with yellow and orange
Widow spiders generally do not infest homes but prefer dark, close quarters outdoors such as woodpiles or crevices under rocks. Indoors they are found in quiet locations such as basements, crawl spaces, and attics typically nesting in narrow gaps between the wall and a stored box or other object. The habit of building their webs between stationary objects and the wall of a structure sometimes allows widow spiders to become a significant pest of warehouses and similar storage facilities.
Black widows are found on the underside to ledges, rocks, plants and debris, including dustbins and outside toilets! They use silk to weave tangled-looking webs, usually near the ground or in dark places. The tips of their legs are non-stick, which prevents them from becoming trapped in their own webs.
The female widow spider lays her eggs in a spherical or tear-drop shaped silk sac (Figure 1) approximately 1/2 inch (~1.25 cm) in diameter. Each egg sac contains between 200 and 400 eggs (more are possible). A single female can produce between four and nine egg sacs in a single summer. The female guards the egg sac and moves it from one location to another within her web to maintain a consistent temperature and humidity. The widow spiderlings hatch approximately eight to ten days after they are laid. The new spiderlings undergo a single molt within the sac and emerge from the egg sac after two to four weeks. The young spiders disperse by ballooning on air currents with a strand of silk. It takes seven additional molts for the young spiderlings to reach sexual maturity. Depending upon geographic location and time of year, the young that survive can reach sexual maturity in as little as three to four months but this is dependent upon suitable temperature and humidity and the availability of prey. Typically, there is only one generation of widow spiders per year. The young overwinter as subadults and become sexually mature in the spring. Mating and egg laying begin shortly after sexual maturity in the late spring.
Type of Damage:
Cobwebs are a nuisance but widow spiders do not damage property. However, like any spider, widow spiders may cause fear and nervousness in people who come into contact with them.
The chief danger from widow spiders lies in their venom. Widow spider venom is one of the few medically significant venoms possessed by a spider in North America. Widow spiders, although not aggressive, do occasionally bite humans. Bites occur most often when someone accidentally presses the spider into his or her flesh by handling something on which the spider has attached its web. This is where the widow spiderâ€™s habit of nesting in woodpiles or in between boxes and crates in garages and warehouses becomes significant. Additionally, adult females guarding egg sacs may also bite if their web is disturbed although they will usually flee. In general, widow spiders are a very timid group of spiders that will only bite when threatened.
Black widow spider toxin contains chemicals that harm the nervous systems of their prey. This means that a quick bite will paralyse prey much larger than the spider, allowing the spider to continue its meal without risk of a further struggle. The spider also injects other chemicals (called enzymes) into its prey that turn the flesh into a soup that the spider can suck up through its tubular mouthparts.
The bite from the widow spider causes a set of symptoms in the bite victim known collectively as latrodectism. Latrodectism is caused by the neurotoxic venom injected by the widow. The initial bite is often painless and goes unnoticed; at worst it will feel like a pinprick. The toxin then travels through the nervous system. The first significant symptom is a dull, numbing ache in the region of the actual bite. This ache may progress to painful muscle cramps in the large muscle masses of the body, particularly the abdomen. Additional symptoms may include sweating, nausea, a rise in blood pressure, leg cramps, muscle tremors, loss of muscle tone, heartbeat irregularities, and vomiting. Symptoms and pain begin between 15 and 60 minutes after the bite and generally peak within one to three hours. Symptoms are usually completely dissipated within 12 to 24 hours. In extremely rare cases (< 1%), death may occur. Very young children and elderly adults are the most susceptible to the widow venom and, therefore, the most likely to experience severe symptoms.
If you suspect that you or one of your children have been bitten by a widow spider, seek medical attention immediately and, if possible, bring the spider with you to the medical center for positive identification.
Family & friends:
Black widows are solitary. They will readily eat other spiders entering their webs – other black widows included!
Keeping in touch:
Generally black widows do not keep in touch. Males must contact a female to mate – and he must approach carefully to avoid being eaten. He vibrates her web in a certain manner that she recognises, allowing him to approach her without risk.
After mating in the spring, the female goes on to lay several egg sacs during the summer months, each containing up to 100-300 eggs. The egg case is about 1.5 mm in diameter and suspended in the web. It is white to tan in colour and has a paper-like texture. Eggs take three weeks to mature at which point up to 100 young may hatch. These are then incubated for 14 to 30 days, after which only one to 12 will survive, due to cannibalism. The females mature in about 90 days and live about three years. By contrast males live only a month or two.
While not at risk of extinction, most people try to kill these spiders on sight due to their dangerous reputation. However, this is often an over reaction as the females will only bite if accidentally handled. For the most part they are shy, retiring little creatures, useful for eating other insect pests. The red widow spider (L. bishopi), a close relative to the black widow, is very rare.
Widow spiders are not the problem they used to be.Historically, outhouses were the primary locations where humans would experience the dreaded widow spider bite. Attracted to the dark, warm area with numerous flying insects, the widow spiders would often nest in the gap beneath the toilet seat. This situation proved particularly dangerous for men!
Female widows donâ€™t deserve their reputation :
The name â€œwidow spidersâ€ came from the belief that the female usually killed and ate the male after mating. It is now known, however, that this practice of â€œhusband killingâ€ was an artifact of the conditions under which observations were made. In early behavioral studies, the male widow spiders were kept in small containers with the females and they could not leave after mating. The usual result was that at some point, the female would mistake the male for prey and he would be eaten. Subsequent studies, both in the laboratory and the field, have shown the female eating the male rarely occurs so long as he is able to leave her web after mating. Interestingly, there is one spider in the same group as the American widow spiders, the Australian redback spider (Latrodectus hasselti), where the female actually begins eating the male as part of the mating ritual. However, this is a unique example among the spiders.
Dangerous but not necessarily deadly:
Although it is true that human deaths have occurred from widow spider bites, it is important to note that modern fatalities from widow bites occur in less than 1 percent of all people bitten. The chances of dying are so low that one researcher compared the chances of dying from a widow spider bite to your chances of being struck by lightning.
- Breene, Robert, 1997. Widow Spiders of North America, American Tarantula Society Publications.
- Drees, B.M. Jackman, J, 1999. Southern Black Widow Spider, Texas A&M University Extension System in association with Texas Cooperative Extension program.
- Edwards, G.B., 2002. Venomous Spiders: Venomous Spiders in Florida, Florida Department of Agriculture and Consumer Services.
- Faith M., 1997. The Black Widow, Alabama Cooperative Extension System, Bulletin ANR-1039.
- Lacey, Mark. 1997. Spiders, Chapter 19, pp 883-909 in A. Mallis and D. Moreland [ed], Handbook of Pest Control 8th edition, Mallis Handbook & Technical Training Company.