The most well known species of the black widow spider is Latrodectus mactans. The latin name means "murderous biting robber." This species occupies most southern areas. Latrodectus variolus is found in extreme parts of southeastern Canada. They live throughout the New England states and parts of Flordia. Latrodectus bishopi is also called a red widow. Brown widows, Latrodectus geometricus, are found in tropical areas. When this spider bites, it is not as severe as the other species of widows. The subspecies Latrodectus mactans tredecimguttatus is also known as a European black widow. Redback spiders, Latrodectus mactans hasselti, are found throughout Australia and some Southeast Asian countries.
When a woman's husband dies, she is called a widow. These spiders receive their common name, "widows" because females sometimes kill their mates.
Latrodectus hesperus is not an endangered species. These spiders can produce large numbers of offspring, and people do not hunt them.
US Federal List: no special status
CITES: no special status
Black widow spiders can be dangerous animals. They have a poisionous venom that is fifteen times as toxic as a rattlesnake. When a spider bites, only a little bit of the venom is injected into the prey. Rattlesnakes are considered more dangerous becuase when they bite, more of the venom is injected into their victim. However, it is important to note that if a large amount of the venom created by the black widow were to get into a human, that person would most likely die. In spite of this, most bites are not fatal. The bite of the black widow is more likely to be painful, and it can cause internal problems. Such side effects include abdominal pain as well as swelling of the muscles in the feet. The more mild symptoms include dry mouth, increased sweating, and swollen eyelids. If a person younger than 16 or older than 60 is bitten, he/she might have to go to the hospital. Most times death from black widow bites results in people between these age ranges because of lung or heart failure. Healthy people who are bitten usually recover in two to five days with the proper care. When a person is first bitten, soap and water works well to clean the area, and one should also apply a cold compress on the bitten area.
Negative Impacts: injures humans (bites or stings, venomous ); household pest
Black widow spiders are not really beneficial to humans except for the fact that they eat insects. Western black widows are often found around human habitations, which makes them a potential predator of pest insects.
Positive Impacts: controls pest population
Western black widows are like most arachnids in that they feed primarily on insects. Because of sticky substances in the silk of a web, black widows are able to catch their prey. The web is made of coarse silk.
The diet of L. hesperus includes beetles, cockroaches, and flies. Black widows kill by means of very small, hollow fangs through which they inject a poisionous venom into their prey. Black widows make small punctures all over the body of their prey, and then proceed to suck out the liquid contents. Because the black widows only take food in the form of liquid, the insect is not fully digested. However, digestive juices of the spider are injected into the insect prey, helping to make more of the prey item edible to the spider. Black widows leave behind the external skeleton of prey insects. These empty shells can be seen near the spider's web. A female black widow may occasionally cannibalize males of the species after mating.
Animal Foods: body fluids; insects; terrestrial non-insect arthropods
Primary Diet: carnivore (Insectivore )
Westerm black widow spiders, Latrodectus hesperus, live in the warmer regions of the United States. This species can be found in all four of the deserts of the American southwest.
Biogeographic Regions: nearctic (Native )
Black widow spiders live under ledges, rocks, plants, and different types of debris. Webs are usually built near to the ground. Webs are sometimes built inside trash cans, piles of trash, as well as under or around houses. When the weather changes from warm to cold, black widows are most likely to find places inside of homes in which to live or spin their webs. in order to prevent black widows from invaiding a home, home owners should remove materials where these animals can hide. If a person happens to find an egg sac, it should be removed with an object other than one's hand.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: desert or dune
Other Habitat Features: urban ; suburban ; agricultural
Males live only a couple of months after reaching maturity. Females can live up to a year after reaching maturity.
Average lifespan
Status: wild: males, 4 months; females, 1.5 years.
Adult female black widow spiders are usually black and shiny. Black widows are most commonly recognized because of the reddish hourglass shape on the underside of the abdomen. Females measure an average of 3.5 cm in length, and typically have a very round abdomen.
Adult males are half the size of females. Their bodies are smaller, but they have longer legs than the females. Males have yellow and red bands and spots dorsally.
Newly hatched black widows are white, but can sometimes be a yellowish-white. As they get older, they slowly turn black. Mature black widows can vary in the amounts of red and white on their bodies.
Average mass: 25 g.
Average length: female, 3.5 cm; males, 1.25 cm.
Other Physical Features: ectothermic ; bilateral symmetry ; poisonous
Sexual Dimorphism: female larger; sexes colored or patterned differently
Black widows are preyed upon by mud-dauber wasps.
Known Predators:
Adult male black widows wander around in search of a female. During this time, males do not bite or feed. First, a male black widow spins a very small web, and then he places a drop of sperm on the web or the silk. He then takes the sperm into special receptacles on the ends of his pedipalps. Afterwards, he searches for a female so that he can place the sperm into the female's genital opening. After the female and male mate in this way, the female lays several bunches of eggs, which contain about 750 eggs. A single bunch of eggs is suspended in a web so that nothing happens to to the eggs before they hatch. A single egg case is about 1 cm in diameter. The egg sac can either be tan or white, and usually has a paper-like texture. Within a given summer, a female may make between 4 and 9 egg sacs. Incubation lasts about 14 days, and the young spiders are cannabalistic. Only one to twelve spiders from an egg sac actually live to be 30 days old.
After males are born, it takes about 70 days for them to mature, and then they die after about a month to two months. In part, this is because females sometimes eat a male after mating takes place. Females, on the other hand, only take about 90 days to mature. Female black widows usually live up to a year and a half.
Average gestation period: 14 days.
Average age at sexual or reproductive maturity (female): 90 days.
Average age at sexual or reproductive maturity (male): 70 days.
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous
Latrodectus hesperus, the western black widow spider or western widow, is a venomous spider species found in western regions of North America. The female's body is 14–16 mm (1/2 in) in length and is black, often with an hourglass-shaped red mark on the lower abdomen. This "hourglass" mark can be yellow, and on rare occasions, white. The male of the species is around half this length and generally a tan color with lighter striping on the abdomen. The population was previously described as a subspecies of Latrodectus mactans and it is closely related to the northern species Latrodectus variolus. The species, as with others of the genus, build irregular or "messy" webs: unlike the spiral webs or the tunnel-shaped webs of other spiders, the strands of a Latrodectus web have no apparent organization.
Female black widows have potent venom containing a neurotoxin active against a range of mammals (see latrodectism). In humans, symptoms of this venom include pain, nausea, goosebumps, and localized sweating. In historical literature, fatalities were reported at anywhere between 0.5% and 12%,[2] but studies within the past several decades have been unable to confirm any fatalities from this or any of the other U.S. species of Latrodectus (e.g. zero fatalities among 23,409 documented Latrodectus bites from 2000 through 2008).[3] The female's consumption of the male after courtship, a cannibalistic and suicidal behavior observed in Latrodectus hasseltii (Australia's redback),[4] is rare in this species. Male western widows may breed several times during their relatively short lifespans.[5] Males are known to show preference for mating with well-fed females over starved ones, taking cues from the females' webs.[6]
Latrodectus hesperus can be found in western regions of North America. In Canada it can be found from British Columbia to Manitoba. They are most commonly found near the Canada-US border, as well as less commonly throughout the grasslands of the Canadian Prairies in Western Canada.[7][8]
The female is stimulated upon contact of a male's web, and vice versa. Male and female L. hesperus produce sexually-specific scents that are combined with their silk; each sex responds by initiating mating when it comes in contact with a web of the opposite sex.[9] On initiating courting, the male L. hesperus will utilize his tarsi to tap the lines of the female's web. The male will continue this tapping gesture with his pedipalps as he actively begins to explore the web. This exploration is intermixed with resting bouts. The male's body spasms, producing a high frequency vibration throughout his abdomen. In many instances, the female will not accept the males sexual display and will scare the male away. In some instances, the females will violently jerk their abdomen, similar to courting male displays, which ultimately leads to a positive reaction from the males and a more successful insemination.[10]
One strategy performed by the male L. hesperus to ensure a successful courtship with the female is to minimize the escape route options for the female within her own web. This is accomplished by the male severing the female's web at various locations that the male believes could provide the female with a course of action to avoid the male. Once the male has successfully made contact with the female's body, he swoons her by gently stroking various parts of her body. The male then creates what is known as the "bridal veil", which is simply silk thrown onto the female.[10]
The time spent on courting varies tremendously and can be as short as ten minutes or as long as two hours. Male's genital bulbs may get injured or partially destroyed in the act of copulation, which leaves him unable to mate again in the future. This may be the reason that many male mates are found dead in the female's web after copulation. Females will often consume these dead males for nutrients to improve her own reproductive success.[10]
Female choosiness can be both evolutionarily advantageous and disadvantageous depending on whether the risk of delaying copulation will inevitably pay off with a better mate, or if it will instead cost the female her whole potential of producing offspring. In fact four percent of female L. hesperus did not acquire mates. The female L. hesperus has the potential to possess more than one mate during their lifespan.[11] This is in part due to the male-bias within the sexually active population of the spider. This sex-bias allows the males to engage in what is known as "scramble competition." Scramble competition means that no male possesses a monopoly over the resource, which in this case is the female spider, yet because there is a finite amount of this resource, those who exploit it faster will come out on top.[12] There are multiple ways in which the female L. hesperus can guarantee her right to choose, one of which is eating the male before copulation. The female receives chemical cues given off by other nearby L. hesperus that indicate the population density, and therefore give them a notion as to whether their choosiness will pay off or fail to do so.[11]
Latrodectus hesperus frequently hangs upside down near center of the web and waits for any insects to enter the web to attack. It bites its victim then wraps it in silk.[13] There are multiple aspects of this spider's web that serve the purpose of capturing prey. The web incorporates hanging gum-footed threads that have liquid glue on them. When prey come into contact with these threads, they get stuck to them, causing the thread to break and the prey to be propelled up by the web to an easy point of access for the spider. The web of L. hesperus also allows for locomotive action by the spider when attacking prey through a sheet of silk.[14] In the months of May through October, there is a significant increase in the amount of prey caught by L. hesperus, presumably because these are the months in which the female produces her egg sacs, and in which the offspring are born and their survival is dependent on their mother's ability to feed them.[15]
Latrodectus hesperus follows prey cues when determining where to settle down. The female L. hesperus is able to detect chemical cues from their prey. As a by-product of this detection, L. hesperus is more likely to build a home in an area that is expressing a high degree of chemical prey cues. This finding may grant us the ability of controlling L. hesperus infestations. By killing off the prey of L. hesperus, there will be a correlated side-effect that pushes L. hesperus to relocate to a location where there are more available prey.[16]
Like other web-building spiders, L. hesperus are polyphagous and feed on prey from eight different arthropod orders. In one study in British Columbia, the orders Coleoptera and Hymenoptera accounted for the majority of the spiders' prey; the majority of prey within Coleoptera were darkling beetles, weevils, and ground beetles, and the most common Hymenoptera were ants, wasps, and bumblebees.[15] The peak activity of hymenopterans in this study was May through September in British Columbia, paralleling a spike in consumption by L. hesperus during these months.[15]
Latrodectus hesperus is an "opportunistic cannibal." There are three circumstances under which L. hesperus may feed on conspecifics: when alternative prey options are scarce; when a spider is starving; in self-defense during antagonistic bouts.[15]
As previously discussed, L. hesperus is an opportunistic cannibal.[15] There of course is variation amongst L. hesperus in terms of how dire a situation must become, or how hungry the spider must be, to resort to cannibalism. Specifically, within siblingships the range of time lapsed before the spider siblings fell victim to cannibalism varied from two days to three weeks. There appears to be a direct relationship between the length of time a L. hesperus will last before falling back on sibling cannibalism and the amount of maternal investment put into their egg sac. In other words, the more investment a mother puts into her egg sac, the longer their offspring will go before engaging in sibling cannibalism as their source of prey and nutrition.[17]
The silk produced by L. hesperus is strongly adhesive.[18] The silk has a fiber at the center covered by some droplets of liquid adhesive protein.[18] When rubbing against one's fingers, it feels like the texture of rubber.[18] The droplets are about twenty times larger than the center fiber's diameter and are visible to the naked eye.[18]
The ultimate strength and other physical properties of L. hesperus silk were found to be similar to the properties of silk from orb-weaving spiders. The ultimate strength for the three kinds of silk measured in the study was about 1000 MPa (145,000 psi). The ultimate strength reported in a previous study for Trichonephila edulis was 1290±160 MPa[19] (188,000 psi). The ultimate strength of mild steel is about 800 MPa (116,000 psi).
Latrodectus hesperus produces three different types of silk: dragline silk, inner egg case silk, and scaffolding silk. Analysis of the amino acid composition of the various silks produced by L. hesperus show that both dragline silk and scaffolding silk are primarily composed of alanine and glycine, in fact neither cysteine nor methionine were detected at all in these silks. In the inner egg case silk, although alanine remained an abundant amino acid, its abundance was less so in this silk than the others.[20]
Latrodectus hesperus' silk contains sexual pheromones which are perceived by the opposite sex upon contact with the web. The males are able to locate the female and begin courting behavior in response to female pheromones. The female curtails her predatory reflexes against the male in response to male pheromones.[10]
L. hesperus produces cobwebs. Cobwebs differ from orb webs, and their architecture can be broken down into three sections. Two sections are utilized to capture prey, the gumfoot threads and the mesh region. The third section provides the structural support for the web and is known as the scaffold threads.[20] The gumfoot lines hang beneath the web, the liquid glue on these lines serves as a sticky substance to trap prey in. The line will break once prey catches on it, creating a tensile force within the web that pulls the line along with the prey up to the spider. L. hesperus seeks refuge in the location from which the web originates and emerges.[14]
Latrodectus hesperus reacts to changes in prey capture by altering its web-spinning behavior. When the spider reaches satiety, it will decrease its energy expenditure on building the features of the web specifically purposed for prey capture. This is evolutionarily advantageous for the spider because it is already satiated. Therefore, it would be a waste of energy to seek out more nutrients. Although there is a decrease in prey-capturing aspects of the web, the overall silk production remains steady or in some cases will increase. L. hesperus also decrease silk investment into webs when preparing for offspring by alternatively increasing silk investment into egg sac production.[14]
The black widow spiders face some predators, like mice, which are omnivorous and larger than the black widow.[18] Juveniles and female adult L. hesperus can eject a chunk of viscid silk toward potential predators.[18] This silk is not toxic, but its mechanical irritation can thwart most predators.[18] However, adult males are unable to produce this defensive silk, presumably because they need to conserve energy for reproduction during their relatively short life span.[18] However, this defensive behavior is very important to females, which are under heavy predation pressure.[18] Black widow spiders spend much time on web construction at night, which is also an active time for ground mice.[18] If the webs are low above ground, it is easy for mice and other predators to attack from below.[18] Since the spider will stay largely stationary at the web hub, such attacks are mostly successful if there is no defensive behavior.[18]
Latrodectus hesperus' bite is similar to that of other Latrodectus species because of their relatedness. The venom is exuded from the spiders' fangs and injected into the enemy. The spiders' prey is paralyzed by the venom, which enables their future digestion. For humans, the venom behaves like a neurotoxin, affecting the neurotransmitter acetylcholine. The female is more of a threat than the male in this species, however her aggressive side only comes out when she is protecting her eggs.[21] Not only are the females fangs larger than the males, but their venomous glands are also more distinct. The effects of their bite can range from a simple irritation to severe autonomic disparities. The venom is composed of proteins, peptides, and proteases. The venom causes an excess release of neurotransmitters which can cause a slew of symptoms. Some of these symptoms include muscle rigidity, perspiration, and nausea. Treatments include painkillers and antivenom if the toxicity is severe enough.[22]
Latrodectus hesperus, the western black widow spider or western widow, is a venomous spider species found in western regions of North America. The female's body is 14–16 mm (1/2 in) in length and is black, often with an hourglass-shaped red mark on the lower abdomen. This "hourglass" mark can be yellow, and on rare occasions, white. The male of the species is around half this length and generally a tan color with lighter striping on the abdomen. The population was previously described as a subspecies of Latrodectus mactans and it is closely related to the northern species Latrodectus variolus. The species, as with others of the genus, build irregular or "messy" webs: unlike the spiral webs or the tunnel-shaped webs of other spiders, the strands of a Latrodectus web have no apparent organization.
Female black widows have potent venom containing a neurotoxin active against a range of mammals (see latrodectism). In humans, symptoms of this venom include pain, nausea, goosebumps, and localized sweating. In historical literature, fatalities were reported at anywhere between 0.5% and 12%, but studies within the past several decades have been unable to confirm any fatalities from this or any of the other U.S. species of Latrodectus (e.g. zero fatalities among 23,409 documented Latrodectus bites from 2000 through 2008). The female's consumption of the male after courtship, a cannibalistic and suicidal behavior observed in Latrodectus hasseltii (Australia's redback), is rare in this species. Male western widows may breed several times during their relatively short lifespans. Males are known to show preference for mating with well-fed females over starved ones, taking cues from the females' webs.