Latrodectus hesperus

Species of spider
Speciesbox
| image = Black Widow making web. jpeg
| image caption = Latrodectus hesperus female
| status system =
| status =
| genus = Latrodectus
| species = hesperus
| authority = Chamberlin & Ivie, 1935 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.

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 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. 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. 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. 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. 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.

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.

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 silk produced by L. hesperus is strongly adhesive. The silk has a fiber at the center covered by some droplets of liquid adhesive protein. (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. 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. 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.