These are two-clawed hunting spiders that are commonly found on the ground or on vegetation. They make flattened, tubular retreats in rolled leaves, under stones, and in leaf litter.

Yellow sac spiders, yellow house spiders, Cheiracanthium mildei, C. inclusum Males are about 6 mm long and females are about 9 mm long. The body of C. inclusum is light yellow, while the body of C. mildei is light green to yellowish white. The median strip on the abdomen is slightly darker than the remainder of the abdomen. Front legs are longer than the hind legs. Chelicerae are brown. The egg-sac is white and papery, and it is usually attached to the underside of objects. Females remain with the eggs until hatching. Juveniles overwinter and molt to adults in the spring; mating occurs in June and July. Natural habitats include leaf litter and around objects on the ground. In the urban environment, these spiders enter houses around doors and windows, heating ducts, and plumbing. They are most common indoors in fall and spring. Inside houses they are found on walls and in corners close to the ceiling; they drop from ceilings on silk threads. Most reports of yellow sac spiders indoors involve Cheiracanthium mildei, which was introduced into North American from Europe (and is distributed in Europe and the Middle East), and C. inclusum, which is native to North America. These two species are very similar in appearance and are generally known as sac spiders, but C. inclusum has also been called the running spider.

European yellow sac spider, Cheiracanthium punctorium

Females are about 12 mm long. The cephalothorax is light brown to brown, while the legs are light brown. The abdomen is yellowish green and pale brown; there is a median brown stripe bordered by yellowish green. In the urban environmenthabitats include webs on walls, and in corners ofrooms. This species is a common and medically important house spider in Europe. The bite of males and females produces symptoms such as intense local pain, itching, vomiting, enlargement of lymph nodes, and fever. This species occurs in Europe, primarily in the Mediterranean region; it is not known to occur in the UK. A closely related species, C. japonicum, occurs in Japan and is commonly found indoors.

Trachelas tranquillus Males are 5-6 mm long and females are 7-10 mm long. The chelicerae and carapace are reddish brown and the cuticle has tiny punctures. The abdomen is pale yellow to light gray, slightly darker anteriorly and medially. Legs 1 and 2 are larger and darker than the other two pairs. Natural habitats include webs in rolled tree leaves; they invade buildings in the fall. It has been reported to bite people, and for mild to serious reactions to occur. This species occurs throughout the USA.

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