Sprucing Up with the Spruce-Fir Moss Spider
The spruce-fir moss spider (Microhexura montivaga) is an incredibly unique species of tarantula endemic to a handful of peaks in the southern Appalachian mountains in the United States. Within this small range, they are found only within spruce and fir forests at elevations above 1,650 m (5,410 ft). M. montivaga relies on the dense carpets of mosses and liverworts that thrive in this environment; these areas are known as sky-islands due to their height and specialized ecosystems.
One of the most interesting traits of the spruce-fir moss spider is that is the world's smallest species of tarantula. Adults measure only 2.5 to 3.8 millimeters (0.10 to 0.15 inch (in) in length, and are medium to dark brown all over. The hair characteristic of tarantulas is minimal, restricted mainly to the abdomen, and the species carries no other distinctive markings.
M. montivaga spends its entire life among the moss patches on the forest floor or low boulders. There, it spins tube-shaped webs for shelter and sheltering their eggs. Rather than using these webs to catch prey, however, the spruce-fir moss spider actively hunts mites and springtails within its home moss patch. Few known predators of this species have been recorded, but likely candidates include pseudoscorpions, centipedes, and other spiders.
Little is known about the reproductive habits of the spruce-fir moss. Females generally lay 7-9 eggs in a single sack in June, and guard it until the spiderlings emerge throughout September. During this time, if predators threaten the nest or the mother is disturbed, she may pick up and move her eggs to a new patch of moss. After hatching, the young spiders take 3-5 years to mature.
Conservation status: The IUCN has yet to evaluate this species; however, it is considered Endangered by the United States Fish and Wildlife Service. Its primary threat is habitat loss due to an invasive pest that damages spruce and fir trees.
Photos
Dr. Marshal Hedin
Kefyn Catley
Gary Peeples