Western black widow spider, Western widow
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.
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DiurnalDiurnal animals are active during the daytime, with a period of sleeping or other inactivity at night. The timing of activity by an animal depends ...
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CarnivoreA carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of a...
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InsectivoresAn insectivore is a carnivorous plant or animal that eats insects. An alternative term is entomophage, which also refers to the human practice of e...
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TerrestrialTerrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, snails), as compared with aquatic animals, which liv...
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OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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FossorialA fossorial animal is one adapted to digging which lives primarily but not solely, underground. Some examples are badgers, naked mole-rats, clams, ...
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Not a migrantAnimals that do not make seasonal movements and stay in their native home ranges all year round are called not migrants or residents.
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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.
The black widow spiders face some predators, like mice, which are omnivorous and larger than the black widow. Juveniles and female adult L. hesperus can eject a chunk of viscid silk toward potential predators. This silk is not toxic, but its mechanical irritation can thwart most predators. 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. However, this defensive behavior is very important to females, which are under heavy predation pressure. Black widow spiders spend much time on web construction at night, which is also an active time for ground mice. If the webs are low above ground, it is easy for mice and other predators to attack from below. Since the spider will stay largely stationary at the web hub, such attacks are mostly successful if there is no defensive behavior.
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. 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.
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. 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.
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.
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. 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.
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.
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.
