Spruce-fir Moss Spider

The spider

An adult spruce-fir moss spider measures two and a half to just under four millimetres, which by the Fish and Wildlife Service’s 1995 listing rule makes it one of the smallest of the mygalomorph spiders. It is light brown to reddish brown, without markings on the abdomen, and has a pair of very long spinnerets at the rear. The rule gave its genus two species, the other in the Pacific Northwest. It lives in mats of moss and liverwort on rocks and boulders in the shade of mature Fraser fir and red spruce, and every mat where it had been found when the rule was written lay under fir. The mats have to be damp and well drained at once. The spider dries out easily, and a large drop of water can harm it.

Mountaintops

Crosby and Bishop described the species in 1925 from spiders collected on a western North Carolina peak in 1923, and Frederick Coyle and William Shear found it again some fifty years later. The recovery plan of 1998 names Mount Mitchell as the type locality and says the population there is believed extirpated. The Service’s species page now gives a range of fewer than twenty-five mountaintops in six areas: Roan Mountain, Grandfather Mountain, the Black Mountains, the Plott Balsams and the Great Smoky Mountains, with one more area in Virginia. The 1998 plan counted Grandfather and Mount LeConte as the surviving populations and the Collins and Clingmans Dome sites as uncertain.

The canopy

The danger is overhead. When the fir canopy dies, more light and less moisture reach the forest floor and the moss mats dry, and the Service’s rule laid the death of the fir to the balsam woolly adelgid, with air pollution, old logging and burning, winter injury and storms as contributors. The Service’s species page adds climate change. Hurricane Helene took an estimated ten to twenty percent of the red spruce canopy on the Roan in September 2024, by the Forest Service’s first assessment as the Southern Appalachian Highlands Conservancy reported it, and the Conservancy named the spider among the species of long-term concern. On Mount Mitchell in May 2023, by the Service’s account, thirty-eight people planted red spruce along the old railroad grade at Camp Alice, and the spider was one of the species the planting was meant to serve.