Nursery web spiders of the family Pisauridae are more diverse than I thought. I had been under the impression that there were only two genera in North America: Pisaurina and Dolomedes. Turns out there is another: Tinus. Thanks to Lynette Schimming at Bugguide.net, I found out that what I thought were immature fishing spiders I had observed in Tucson, Arizona and Mission, Texas were actually adults of Tinus peregrinus.
Whereas most adult fishing spiders and nursery web spiders are quite large (body length 10-28 mm), Tinus peregrinus maxes out at around 10 millimeters body length, males a millimeter shorter still.
This species ranges across the southwest U.S. from southern California to the southern tip of Nevada, and east to Texas and Missouri. It also occurs in northern Mexico. The “type locality,” the site where the first known specimen was collected, is listed as Hot Springs, Arkansas, but it is suspected that this is in error.
Virtually nothing is known of the life history and biology of this animal. Egg sacs in preserved collections are dated late July and early August. I have observed this species under bark on trees near the edges of ponds, and also at the edges of window frames. It would appear that once an individual spider finds a location that suits it, the spider stays put. One specimen I found in the corner of a window had several shed exoskeletons in its web, suggesting it had resided there for some time. No wonder, the web was also full of tiny midges (flies in the family Chironomidae) that had swarmed the lighted building at night.
Like most spiders in the Pisauridae, T. peregrinus appears to prefer the vertical plane, rarely found on the ground.
Sources: Carico, James E. 1976. “The Spider Genus Tinus (Pisauridae),” Psyche 83: 63-78
Kaston, B. J. 1978. How to Know the Spiders (Third Edition). Dubuque, Iowa: Wm. C. Brown Company Publishers. 272 pp.