Yellow Sac Spiders
Order: Aranae
Family: Clubionidae
Scientific Name: Cheiracanthium
The 200 species of Clubionids found in North America are commonly referred to as the two-clawed hunting spiders. Members of the genus Cheiracanthium are called sac spiders. Cheiracanthium mildei (L. Koch) and C. inclusum (Hentz) are the two spiders referred to as yellow sac spiders, or yellow or tan house spiders, depending on locale.
They
have been associated with numerous cases of human arachnidism (spider
bites).
These spiders are suspected of being responsible for most indoor
arachnidism; in the United States, however, neither severe trauma nor
deaths have been reported.
Their venom is cytotoxic, mainly affecting tissues at the site
of the bite.
Identification
The common characteristic of this group of spiders is that each tarsus (tip of the leg) has two claws. In addition, C. mildei is light green to yellow white in color. There is a dark strip on the anterior portion of the upper-midline of the abdomen. The female body is 8-10 mm (1/3 inch) long, whereas the male body is approximately 6 mm (1/4 inch) long.
Eight eyes similar in size are arranged in two rows across the front of the cephalothorax (head and thorax). The chelicerae (jaws) are brown, as are the tips of the palpi. The legs appear very smooth because the hairs and spines are very short and inconspicuous. The front legs are longer than the rear legs.
Males
can be distinguished from females by their longer legs, enlarged and modified
palpi and more slender abdomen.
The egg sac is a white paper-like disk which is usually attached
in a protected area, such as under a stone.
Life Cycle and Habits
The indoor population of this spider increases significantly in the fall when the weather turns cool and outdoor food sources decline. They use cracks around utilities, windows and doors to gain entry.
Spiders can be found inhabiting wall voids or silken retreats (sacs) constructed in the upper corners of rooms. They rest in these protected areas during the day, and at night aggressively hunt prey. Sac spiders often roam ceilings and walls seeking prey. However, if they fall to the floor, they rapidly seek a protected area. They often prey upon overwintering arthropods in wall voids or other less capable spiders.
Control
Preventive treatment begins by sealing all entry points into the structure and eliminating pests that may serve as a food source. Trim branches, vines, and other shrubbery so they do not contact the structure. Apply insecticides such as wettable powder or microencapsulated formulations around the foundation and potential entry points to help in prevention.
Corrective
action begins with vacuuming up egg sacs, spiders, and their silken retreats.
This reduces potential yellow sac spider problems.
Consider using residual insecticides in these harborage areas.
(Courtesy of the National Pest Control Association.)