The small wolf spiders of the genus Pardosa (Lycosidae), commonly called the thin-legged wolf spiders, are distributed throughout the world, mainly in temperate and boreal regions. The genus comprises more than 500 species, which occur in many habitats, from deciduous woodlands to Arctic tundra. Few, however, occur in the type of harsh habitat depicted here: a shoreline of bare, surf-splashed rocks at the edge of the open Atlantic Ocean.
Along this stretch of rocky coast at Ogunquit, Maine, I found many Pardosa specimens earlier this week. The spiders I found were probably of the species Pardosa lapidicina, commonly called the stone spider. The body length of this species is typically no longer than 9 mm. In addition to the dark variety shown above, there is also a pale color morph:
As its scientific and common names indicate, P. lapidicina is a lithophilic species. In northeastern North America, these spiders can often be seen on rocky coasts during the summer and early autumn. They seem to be chiefly diurnal. The spiders that I observed were alternately sheltering in dark crevices and sallying forth to dart across rock surfaces, presumably to hunt for insects that land on the sun-warmed substrates.
I saw these spiders on rocks as near as one meter to the crashing, sloshing waves at the water's edge. In fact, during low tides, P. lapidicina sometimes makes forays into the intertidal zone to hunt for tiny prey animals. Some researchers report that spiders of this species can even survive temporary submersion in seawater during high tides. (See Douglass H. Morse, Distribution, movement, and activity patterns of an intertidal wolf spider Pardosa lapidicina population (Araneae, Lycosidae), Journal of Arachnology, 25(1), 1997, pages 1–10.)
While P. lapidicina often overwinters at the shore, where the spiders retreat deep into crevices or beneath stones, research has found that in late autumn some spiders may migrate to more protective leaf-litter environments in adjacent brushy or forested areas. (See Johanna M. Kraus and Douglass H. Morse, Seasonal habitat shift in an intertidal wolf spider: proximal cues associated with migration and substrate preference, Journal of Arachnology, 33(1), 2005, pages 110–123.)