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Latrodectus hesperus
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Latrodectus hesperus
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 red, yellow, and on rare occasions, white. The male of the species is around half this length, and generally a beige 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 (α-latrotoxin) active against a range of organisms. In humans, symptoms of this venom include pain, nausea, vomiting, 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 any of the 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, 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.
Latrodectus hesperus can be found in the South-western regions of Canada, from British Columbia to Manitoba, along the Pacific Coast and throughout Texas, Oklahoma and Kansas in the U.S., and in Mexico. They are commonly found near the Canada-US border, as well as less commonly throughout the grasslands of the Canadian Prairies in Western Canada.
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 its tarsi to tap the threads of the female's web. The male will continue this tapping gesture with its pedipalps as it actively begins to explore the web. This exploration is intermixed with resting bouts. The male's body spasms, producing a high frequency vibration throughout its abdomen. In many instances, the female will not accept the male's 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 is to minimize the female's escape route options within its own web. This is accomplished by the male severing the female's web at various locations that it 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, it swoons the female by gently stroking various parts of its 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. A male's pedipalps may get injured or partially destroyed in the act of copulation, which leaves it 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 can consume these dead males for nutrients to improve their own reproductive success.
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 its whole potential of producing offspring. The female L. hesperus has the potential to possess more than one mate during their lifespan. 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, because there is a finite amount of this resource; those who exploit it faster will come out on top. There are multiple ways in which the female L. hesperus can guarantee its right to choose, one of which is eating the male before copulation. However as mentioned, this is an extremely rare behaviour in L. hesperus. 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 not.
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Latrodectus hesperus
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 red, yellow, and on rare occasions, white. The male of the species is around half this length, and generally a beige 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 (α-latrotoxin) active against a range of organisms. In humans, symptoms of this venom include pain, nausea, vomiting, 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 any of the 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, 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.
Latrodectus hesperus can be found in the South-western regions of Canada, from British Columbia to Manitoba, along the Pacific Coast and throughout Texas, Oklahoma and Kansas in the U.S., and in Mexico. They are commonly found near the Canada-US border, as well as less commonly throughout the grasslands of the Canadian Prairies in Western Canada.
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 its tarsi to tap the threads of the female's web. The male will continue this tapping gesture with its pedipalps as it actively begins to explore the web. This exploration is intermixed with resting bouts. The male's body spasms, producing a high frequency vibration throughout its abdomen. In many instances, the female will not accept the male's 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 is to minimize the female's escape route options within its own web. This is accomplished by the male severing the female's web at various locations that it 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, it swoons the female by gently stroking various parts of its 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. A male's pedipalps may get injured or partially destroyed in the act of copulation, which leaves it 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 can consume these dead males for nutrients to improve their own reproductive success.
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 its whole potential of producing offspring. The female L. hesperus has the potential to possess more than one mate during their lifespan. 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, because there is a finite amount of this resource; those who exploit it faster will come out on top. There are multiple ways in which the female L. hesperus can guarantee its right to choose, one of which is eating the male before copulation. However as mentioned, this is an extremely rare behaviour in L. hesperus. 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 not.
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