Spruce-Fir Moss Spider

The spruce-fir moss spider was originally described by researchers based on collections made from a mountain peak in western North Carolina in 1923 and only a few specimens were taken. Little was known about the species until its rediscovery approximately 50 years laterin 1981. Microhexura montivaga is one of only two species belonging to the genus Microhexura in the family Dipluridae. The other species in the genus, M. idahoana, occurs only in the Pacific Northwest. Diplurids belong in the primitive suborder Mygalomorphae, which are often popularly referred to as ``tarantulas''. The genus Microhexura is the northernmost representative of the family Dipluridae and is also one of the smallest of the mygalomorph spiders, with adults measuring only 2.5 to 3.8 millimeters (0.10 to 0.15 inch). Coloration of M. montivaga ranges from light brown to a darker reddish brown, and there are no markings on the abdomen. The carapace is generally yellowish brown. The most reliable field identification characteristics for the spruce-fir moss spider are chelicerae that project forward well beyond the anterior edge of the carapace, a pair of very long posterior spinnerets, and the presence of a second pair of book lungs, which appear as light patches posterior to the genital furrow. The typical habitat of the spruce-fir moss spider is found in damp but well-drained moss (and liverwort) mats growing on rocks or boulders, in well-shaded situations in the mature, high-elevation Fraser fir (Abies fraseri) and red spruce (Picea rubens) forests.

There is no record of prey having been found in the webs of the spruce-fir moss spider nor has the species been observed taking prey in the wild, but the abundant springtails (collembolans) in the moss mats provide the most likely source of food for the spider. Males of the species mature during September and October, and females are known to lay eggs in June. The egg sac is thin- walled and nearly transparent, and it may contain seven to nine eggs. The female remains with the egg sac and, if disturbed, will carry the egg sac with her fangs. Spiderlings emerge in September. The life span of the species is also unknown, but estimated to be 3 years for the species to reach maturity.

From 1989 through 1992, status surveys were conducted for the spruce-fir moss spider and based on the results of these surveys, the spider is presently known to exist at only four locations--three sites in North Carolina and one in Tennessee. Of the four remaining populations, only one appears to be relatively stable. This population is located along the Avery/Caldwell County line in North Carolina. The other two populations in North Carolina are located in Swain County. Both of the Swain County populations are extremely small with only one spruce-fir moss spider having been found at each of these two sites in recent years. The forests at the two Swain County sites are rapidly declining. The Tennessee population is located in Sevier County. This population was considered healthy in 1989 but is currently believed to be declining in numbers and is endangered by habitat loss/alteration. The high-elevation spruce-fir forests throughout much of the species' historic range are being decimated by the balsam wooly adelgid (Adelges piceae)--an exotic insect pest--and possibly by air pollution (acid precipitation) and other factors not yet fully understood. The death and thinning of the forest canopy results in locally drastic changes in microclimate including increased temperatures and decreased moisture leading to desiccation of the moss mats on which the spruce-fir moss spider, and possibly its prey base, depend for survival.

This spider was placed on the federal endangered species list in March, 1995 and is protected under the endangered species act

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