Cheiracanthium inclusum, alternately known as the black-footed yellow sac spider or the American yellow sac spider (in order to distinguish it from its European cousin C. punctorium), was formerly classified as a true sac spider (of the family Clubionidae), and then placed in the family Miturgidae, but now belongs to family Cheiracanthiidae. It is a rather small pale yellow species that is indigenous to the Americas. It is often found living in the foliage of forests and gardens but also can inhabit human homes. Despite common beliefs of necrosis, Cheiracanthium bites cause only localized swelling. C. inclusum is closely related to Cheiracanthium mildei, an introduced species native to Europe which is similar in appearance and natural history and can also be found in North American homes.

Identification

Like all spiders, C. inclusum has two body segments: a cephalothorax (fused head and thorax) and an abdomen. In females, the body measures between 5 and 9 mm and in males, 4 to 8 mm. The leg span however can be up to with the front pair of legs being longer than the other 3 pairs. Males tend to have a narrower body and a larger leg span than females.

Natural history

Distribution

C. inclusum are native to the New World (North, Central, and South America; and West Indies). This species has also been introduced to Africa and Réunion. They are most often found in trees and shrubs, but may also find shelter in houses and other human-made structures. During the day, they retreat in small silk nests similar to those used for reproduction. A new nest, which may be completely closed, open on one side, or open on both sides, is built every day in under 10 minutes.

C. inclusum are known to disperse easily between trees and shrubs. They do this by excreting a long silk thread that gets carried by the wind and sticks to a nearby structure, forming a scaffold between two structures. Alternatively, the spider may stay attached to the thread and balloon through the air.

References

  • The Nearctic Spider Database
  • Photo
  • Pictures of C. inclusum (free for noncommercial use)
  • U Arkansas – Arthropod Museum Notes by Jeffrey K. Barnes