Spruce Fir Moss Spider, Microhexura montivaga

The Spruce Fir Moss Spider (Microhexura montivaga) is an endangered species of spider that can be found at high elevations in the southern Appalachian Mountains. Initially identified in 1923, they inhabit moss that grows on rocks under the forest canopy.

It is one of the smallest mygalomorph spiders, with the adults only measuring 3 to 4 millimeters. The coloration varies from light brown to yellow-brown to a darker reddish brown color, with no markings on its abdomen. Their chelicerae project forwards and one pair of spinnerets are rather long. They possess a second pair of book lungs, which appear as light patches behind the genital furrow.

These spiders construct tube-shaped webs, apparently for the purpose of shelter, for prey has never been found in them. They most likely feed on the springtails that are abundant in the moss mats. The spiders can spend as long as three years reaching maturity because of the low temperatures and resulting in a slow metabolism.

The widespread death of Fraser fir trees has demolished many habitats for these spiders, resulting in their enlistment as endangered in 1955.

It is known from Fraser fir and red spruce forests on mountain peaks at and above 1,650 meters in the Southern Appalachian Mountains in North Carolina and Tennessee. They have also been recorded from Clingmans Dome and Mount Collins, Mount Le Conte, Mount Mitchell, Grandfather Mountain and Roan Mountain.

Image Caption: Spruce-fir moss spider, Microhexura montivaga. Credit: SheepNotGoats/Wikipedia