Common Name: Spider - Black widow
Latin Name: Latrodectus
Common Family Name: Comb-footed spiders
Latin Family Name: Theridiidae
Other Names: Brown widow
Origin: Five species of these native spiders occur in North America, being found in all states and in southern Canada. Other species may be found worldwide.
Biology: The black widow spiders are the most dangerous spiders with respect to human health in the U.S. They are one of the few spiders capable of biting humans that inject a neurotoxin, and the effect of the bite can be serious and potentially fatal. Only females bite humans, but both males and females construct webs to capture other prey, primarily flying insects. Males also enter a female’s web for mating, and if the female is not receptive the male may be eaten. The life span of black widow females averages around 180 days as an adult, taking about 3 months to reach maturity. Males mature in about 70 days and live only about 30 days after that. The female may produce up to 9 egg sacs with about 350 eggs per sac on average. She will be most aggressive and defensive of her webbing while she is guarding these eggs, as well as being more hungry following egg production. The new spiderlings emerge from the sac and remain near it for a day or two, but then they undergo “ballooning” to disperse, creating long silk strands that are carried away by the wind. Black widows are generally reclusive spiders that create their webs in areas of inactivity. The web is made of extremely strong silk that is very sticky, and it has a very haphazard appearance without the symmetry of some other spiders.
Identification: Females are the most recognized spider in North America, with their shiny black body, long thin legs, large oval abdomen, and red “hourglass” pattern on the underside of the abdomen. This hourglass pattern may not always be there. Males also have the same pattern, but it is white, and their body color is mottled brown and white. Immature spiders begin very light colored and progress to the adult color in stages as they pass through their instars, gradually becoming more black if they are females. The female tends to hang upside down in her web due to the weight of the abdomen. Eggs sacs of black widows are about ½ inch in diameter and are smooth surfaced. The eyes of comb-footed spiders are typically a total of eight eyes arranged in two rows of four eyes, one row above the other and with the outside eyes so close together that they touch each other.
Characteristics Important in Control: Elimination of unnecessary debris in storage or on the exterior will reduce harborage sites, including lumber or firewood piles, boards or other materials on the ground, and yard debris. Materials stored in garages or other interior storage areas can be kept off the floor and in a condition that allows access to the areas behind them. The individual spider inside may be eliminated by vacuuming, and the webbing then removed with a sweep. For chemical control the pyrethroid insecticides are excellent, giving quick knockdown and kill and a lengthy residual.
Common Name: Spider - Violin spider
Latin Name: Loxosceles
Common Family Name: Brown spiders
Latin Family Name: Loxoscelidae
Other Names: Brown recluse spider, fiddleback spider
Origin: There are 11 species of Loxosceles that are native to the United States, and at least one imported species that is found in the southwest. The Brown Recluse, L. reclusa, has the widest range, from a small area of western Florida to Texas and north to Iowa. It has been found sporadically as a transient in other states. The other 10 native species are found in the southwest from Texas to California.
Biology: The Brown Recluse, Loxosceles reclusa, has a reputation that far exceeds reality. It is a hunting spider that uses it web only for lining its retreat and for covering its eggs. It is very capable of biting humans, and the venom is a cyto-toxic venom which causes tissue death at the site of the bite, possibly leading to a large, infected, and lingering wound. However, experts believe that most skin infections blamed on this spider’s bite are actually bacterial infections, particularly in states with very high reported bites but very low confirmed presence of the spider. The Brown Recluse lives commonly in structures, hiding with clothing, behind furnishings, or in attics and wall voids. Young spiders take about one year to mature and the adults live about one year more. They prefer to remain in areas of low activity and are not aggressive, biting only when provoked to do so by becoming trapped and threatened with harm.
Identification: These are light to dark brown spiders with very long legs and short hairs covering the legs and body segments. On the top of the cephalothorax there usually will be a darker pattern that strongly resembles a violin, giving this genus its common names of “violin” or “fiddleback”. However, many other spiders also have this vague pattern, and positive identification cannot be made based only on this character. The eyes of Loxosceles are very distinctive for the genus. There are 6 eyes arranged as 3 pairs in an arc across the front of the cephalothorax. No other spiders have this eye arrangement, and it can be seen easily with low magnification.
Characteristics Important in Control: General cleanup of unnecessary debris outside will reduce harborage sites, and cleanup of clutter in garages or storage areas will reduce the numbers of spiders living on the interior. If invading spiders become a problem they can be prevented with an application of a residual pyrethroid insecticide around the building exterior and in likely pathways along walls on the inside. The use of glue traps can confirm the presence of the spiders, placed in attics or along wall-floor junctions. Dust formulations can be injected into walls or other voids the spiders may inhabit. Since structures can be re-infested from surrounding areas the habitat of this spider should be pushed as far away from the structure as possible. Heavy vegetation cover on the ground should be kept away from the structure, and all debris and materials on the soil that do not have to be there should be eliminated. Trees and shrubs that grow near the structure should be physically separated by pruning, and all cracks or other openings to the structure that can be repaired should be permanently sealed.
Common Name: Spider - Hobo spider
Latin Name: Tegenaria agrestis
Common Family Name: Funnel web spiders
Latin Family Name: Agelenidae
Other Names: Aggressive house spider, funnel weavers, domestic house spider
Origin: At least 7 species of spiders in the genus Tegenaria occur in North America, with only T. chiricahuae a native, and occurring in Arizona and New Mexico. The other six species are believed to be European in origin, with T. domestica found throughout the U.S. and T. agrestis found in the Pacific Northwest states. The family contains many other genera and over 400 species of spiders.
Biology: The most notorious species in this group is T. agrestis, variously called the Aggressive House Spider or Hobo Spider, and it is known to bite with little provocation. Like many spiders it has venom which is cyto-toxic, and tissue death at the site of the bite, leading to a lingering open wound, is very possible. It is a very common spider in structures in the Pacific Northwest, and is the most likely cause of serious spider bites there. Species of Tegenaria usually live about two years, and with T. agrestis the first year is spent developing to the adult stage, the second summer is for mating and egg production, and the adults die shortly after this. The family name is derived from the prey capture habit of these spiders, which create wide mat of webbing with a funnel-like hole in it, and the spider waits within this funnel for prey to stumble onto the web mat. The spider then rushes out, subdues the prey, and drags it back into the funnel for feeding. The funnel-web mats may be on vegetation or near the soil, or possibly within structures in undisturbed areas.
Identification: Since Tegenaria appears to be the most important group of spiders in this family the description will be for them. These are fairly large spiders, with adult bodies about ¾ inch long and with very long, hairy legs. There are several longitudinal dark stripes on the top of the cephalothorax and the top of the abdomen exhibits a distinct “herring-bone” pattern of darker, zig-zag lines. There are eight eyes in Tegenaria, arranged in two rows across the front of the “face” area, and with the posterior row strongly curved to the back, and the outer pairs of eyes nearly touching.
Characteristics Important in Control: Since these spiders pose a definite human health threat they do need to be controlled when found living in structures. Habitat modification, to remove all possible harborage sites, is a vital component of control of this group. Exterior vegetation should be trimmed well away from the structure, grassy areas kept mowed, and piles of lumber or firewood maintained properly and well away from the building. Any unnecessary objects on the soil need to be removed. On the interior cleanup of clutter is important, along with physical removal of webbing. Exclusion techniques need to be employed to close any potential gaps or holes the spiders may use to enter the building. Chemical applications include the use of a dust insecticide within cracks and voids that may harbor the spiders, as well as an application of a residual pyrethroid insecticide around the exterior and to likely spider areas inside.
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