Widow spider

Widow spiders
Black Widow spider
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Arachnida Order: Araneae Family: Theridiidae Genus: Latrodectus
Species
Approx. 31, see article

The widow spiders are members of the spider genus Latrodectus, a subset of the family Theridiidae. Latrodectus includes approximately 31 recognized highly poisonous species, with the Black widow spiders (Latrodectus mactans) being the best known members of the group. Envenomation by these spiders can be fatal to children and ill or infirm adults. Ordinarily, the body mass of a healthy adult is sufficient to dilute the venom to less than a fatal concentration.

Spiders of the genus Steatoda (also of the Theridiidae family) are often mistaken for widow spiders, and are known as False Widow Spiders. The false widow spiders are significantly less harmful to humans.

Along with the Latrodectus mactans, the glossy black ones with the famed red hourglass, the gray widow spiders (Latrodectus geometricus), the red widow spiders (Latrodectus bishopi), the northern widows (Latrodectus variolus), and the western widows (Latrodectus hesperus) (Preston-Malfham, 1998) are also found in the United States. But there are widow spiders on every continent of the world except for Antarctica. In some areas in Africa this Genus receives the generic name "button spiders."

In common with other members of the Theridiidae family, the widow spiders construct a cobweb, i.e., an irregular tangle of sticky silken fibers. The black widow spider very frequently hangs upside down near the center of its web and waits there for insects to blunder in and get stuck. Then, before the insect can extricate itself, the spider rushes over to bite it and swathe it in a silken shroud. If the spider feels threatened it will normally let itself down to the ground on a safety line of silk just as fast as it can. As with other web-weavers, these spiders have very poor eyesight and depend mostly on vibrations reaching them through their webs to orient themselves to prey or warn them of larger animals that could injure or kill them. They are not aggressive, and most injuries to humans are due to defensive bites delivered when a spider gets unintentionally squeezed or pinched somehow. It is possible that some bites may result when a spider mistakes a finger thrust into its web for its normal prey, but ordinarily intrusion by any large creature will cause these spiders to flee.

Species

The silk of the Latrodectus genus is larger in diameter than the silk of other spiders, and, as with all spider silk, it is stronger than an equal-sized filament of steel. Because of these excellent characteristics it was in great demand to use in the construction of reticles for rifle sights at least as late as World War I.

The black widow spider, Latrodectus mactans, has a prominent red hourglass figure on the underside of its abdomen. Many of the other widow spiders have red patterns on a glossy black or dark background, which serve as a warning. Some of the more well known species of widow spiders are listed below, together with some of the areas where they are found. This list should not be considered complete.

• Latrodectus atritus, the black katipo, found in New Zealand
• Latrodectus bishopi, the red widow, Florida, USA
• Latrodectus curacaviensis, Americas
• Latrodectus dahli, S Europe, N Africa, SW Asia
• Latrodectus geometricus, the brown widow or grey widow, Africa, USA
• Latrodectus hasselti, the red-back spider, Australia
• Latrodectus hesperus, the Western black widow, western USA
• Latrodectus hystrix, S Europe, N Africa, SW Asia
• Latrodectus katipo, the red katipo, found in New Zealand
• Latrodectus indistinctus, the button spider, S. Africa
• Latrodectus karooensis, S. Africa
• Latrodectus lugubris, Kazakhstan and Central Asia
• Latrodectus mactans, the Southern black widow spider, warm regions of the USA
• Latrodectus pallidus, the white widow, S Europe, N Africa, SW Asia
• Latrodectus renivulvatus, S. Africa
• Latrodectus rhodesiensis, South Africa
• Latrodectus tredecimguttatus, the Mediterranean Black Widow (or European Black Widow), Mediterranean area
• Latrodectus variolus, the Northern black widow, from the extreme southeastern part of Canada and south to northern Florida, with frequency higher in the northern part of this range.

References

• Discovery Books; 2000; Insects and Spiders; St. Remy Media Inc.; New York; 35
• Freeman, Scott; 2003; Biological Science; Prentice-Hall
• Hillyard, Paul; 1994; the Book of Spiders; Random House, Inc.; New York; 47-50
• Hillyard, Paul; 1994b; The Book of the Spider; Avon Books; New York; 22-25
• Martin, Louise; 1988; Black Widow Spiders; Rourke Enterprises, Inc.; 18-20
• Preston-Malfham, Ken; 1998; Spiders; Chartwell Books; Edison; New Jersey; 40.
• "Arthropod," Microsoft® Encarta® Online Encyclopedia 2004

External links

Steatoda:

• http://www.puyallup.wsu.edu/plantclinic/resources/pdf/pls107steatodaspider.pdf
• http://www.zoo.org/educate/fact_sheets/spiders/f_widow.html