|Latrodectus hesperus female|
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.) Symptoms are pain, nausea, goosebumps, and localized sweating. Fatalities have been reported at between 0.5% and 12%. 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 less commonly throughout prairies regions of the Canadian Prairies in Western Canada.
Female stimulates by contact with male webs Male and female Latrodectus hesperus produce sexually specific scents which are combined with their silk; each sex responds by initiating mating when it comes in contact with a web of the opposite sex.
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.
Latrodectus hesperus has a few parasites or predators known to affect them; parasites include wasps in the family Scelionidae and flies in the family Acroceridae, and flies in the genus Pseudogaurax, while the most common predator is the wasp Chalybion californicum.
Interactions with humans
Latrodectus hesperus often live in human dwellings, usually in cluttered dark areas. It has poor eyesight, and detects danger by silk vibration.
Only female spiders have fangs long enough to pierce the skin, and so cause a bite to be harmful and require medical treatment.
L. hesperus is one of the most commonly studied spider species when investigating spider silk. This is due to several factors, including the prevalence of black widows in nature, the relative ease of caring for black widows compared to other spiders, the quality of black widow silk, and the large amount of gene sequencing research that has been done on black widows.
Like other spider silk proteins, L. hesperus silk exhibits unusually high mechanical strength, extensibility, and toughness. 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 that had been tested in other studies. The ultimate strength for the three kinds of silk measured in the study was about 1000 MPa. The ultimate strength reported in a previous study for Nephila edulis was 1290±160 MPa (The ultimate strength of mild steel is about 800 MPa, while Kevlar® is about 3.62 GPa). However, as steel and Kevlar® are not very elastic and spider silk is extremely elastic, the silk is able to absorb 3-10 times as much energy as Kevlar®; this is why spider silk is reported to be the toughest material on the planet.
The exceptional properties of spider silk arise from the protein sequence and structure of the silk, which in black widows’ dragline silk is a blend of at least two distinct proteins: MaSp1 (Major Ampullate Spidroin 1) and MaSp2 (Major Ampullate Spidroin 2). These proteins have been (and will continue to be) the subject of a large amount of protein sequencing research, as their immense size (200-350 Kg/mol, or about 10x larger than the largest commercial polymers) makes them hard to study with typical techniques like nuclear magnetic resonance spectroscopy and molecular dynamics modeling.   In MaSp1, the majority of the protein is a hydrophobic strand consisting of a polyalanine motif alternating with a glycine-rich GGX motif, where X is usually alanine, glutamine, or tyrosine. In MaSp2, the polyalanine motif is preserved, but the glycine block is changed from GGX to a proline-rich GGX1GPX2, where X1 is often alanine or glutamic acid and X2 is glycine or alanine. The polyalanine motifs are able to stack into β-sheets, yielding crystallites in the silk that provide strength in a mechanism reminiscent of precipitate strengthening in metals, while the glycine- and proline-rich motifs form amorphous regions that give the silk its elasticity. In both MaSp1 and MaSp2, the termini of the protein sequences form hydrophilic α-helix-rich regions that are able to dimerize with other termini, entangling multiple proteins together. The specific effect of this dimerization process, as well as how silk proteins pack together and assemble into fibers, is a current area of research at many universities and private companies. In 2018, researchers at Northwestern University and San Diego State University found that the spider's silk fibers originate as nanoscale hierarchical assemblies of spidroin micellar nanoparticles in the silk glands prior to spinning. Understanding the process of converting responsive micelle structures into mechanically superior fibers has applications in improving high-strength textiles manufacturing for military and athletic uses and in developing stronger building materials.
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