Description

Adults are relatively large, plain brown to grayish-brown spiders. The forepart of the body (cephalothorax) is often darker in color than the abdomen to varying degrees. Males are smaller and much slenderer bodied than females, 0.31-0.47 inches (8-12 mm) in body length. Females are 0.47- 0.7 inches (12-18 mm) in body length, with a robust, rounded abdomen and broader cephalothorax. When the legs are extended, they give the impression of a much larger spider. Males are distinctive in possessing a pair of unusually elongated appendages (pedipalps) in front of the legs that give the impression of an extra pair of legs when extended. This feature alone distinguishes the males from brown recluse spiders, for which they are often mistaken. Both sexes are typically larger than brown recluses, and females are much more heavily bodied. As with most spiders, eye arrangement is an important technical character for classification to family.

Females and immature spiders build disorganized, tangled webs with a circular tunnel in one corner that leads to a secluded crack or crevice. In fact, the family that includes this species, Filistatidae, goes under the common name “crevice weavers.”

Southern house spider female with web. Joseph LaForest, University of Georgia, Bugwood.org.

Life Cycle

Females and immatures hide in a portion of the web that extends into a sheltered crack or crevice, where they wait for prey to become trapped in the web. The spider then rushes out, bites the prey to immobilize it and drags it into the lair to consume. Females produce round egg sacs that are similar in structure to the silk of the web. Mature males do not build webs, but they actively search for prey and potential mates. In Louisiana development may be continuous year-round both indoors or outdoors during periods of mild weather. Females reportedly live for up to eight years.

Ecological Significance and Pest Status

Southern house spiders are harmless to humans. They are reluctant to bite, and the venom is not medically significant. They may build up populations in unkept areas of houses, outbuildings, warehouses and similar structures in addition to outdoor habitats. The size, slender build, and nondescript brown external appearance of males leads to many misidentifications of this species as the brown recluse (Loxosceles reclusa). These cases can result in unfounded anxiety and unnecessary treatment of structures. The coarse, tangled webs of the females in corners and near cracks in walls and ceilings are diagnostic for the presence of the species, and wandering males can be expected in such circumstances.

Control

The unsightly webs can be safely removed with a broom or vacuum, and harborages and points of entry can be sealed. Sealing structures properly not only prevents re-infestation by spiders but eliminates the prey base that they feed upon. Eliminating the population of females will eventually result in the disappearance of males. However, if the webs and known presence of the spiders are not a problem, consideration should be given to leaving them alone as free pest control.

References

Barrantes, G., and M. J. Ramirez. 2013. Courtship, egg sac construction, and maternal care in Kukulcania hibernalis, with information on the courtship of Misionella mendensis (Araneae, Filistatidae). Arachnology 16: 72-81.

Vetter, R. S. 2009. Arachnids misidentified as brown recluse spiders by medical personnel and other authorities in North America. Toxicon 54: 545-547.