Microhexura montivaga
ORDER
Araneae
FAMILY
Dipluridae
TAXONOMY
Microhexura montivaga Crosby and Bishop, 1925, Mount Mitchell, North Carolina, United States.
OTHER COMMON NAMES
None known.
PHYSICAL CHARACTERISTICS
One of smallest spiders, with adults of length 0.10–0.15 in (0.25–0.38 cm). Ranges in color from light brown to darker reddish brown. No markings on abdomen. Carapace is mostly a yellowish brown. Chelicerae are projected forward beyond anterior edge of carapace. Possesses pair of extremely long posterior spinnerets. Second pair of book lungs, which appear as light areas, is posterior to genital furrow.
DISTRIBUTION
Found only at the highest mountain peaks, at and above 5,400 ft (1,645 m) in elevation, in the southern Appalachian Mountains of western North Carolina and eastern Tennessee (Untied States). Recorded from Mount Mitchell, Yancey County, North Carolina; Grandfather Mountain, Watauga, Avery, and Caldwell Counties, North Carolina; Mount Collins, Swain County, North Carolina; Clingmans Dome, Swain County, North Carolina; Roan Mountain, Avery and Mitchell Counties, North Carolina, and Carter County, Tennessee; Mount Buckley, Sevier County, Tennessee; and Mount LeConte, Sevier County, Tennessee. Experts believe that the Mount Mitchell population has been killed off.
Ongoing surveys show that reproducing populations still survive on Grandfather Mountain in North Carolina, but are restricted to small areas of microhabitat. Both the Mount Collins and Clingmans Dome populations, if still present, are extremely small. On Roan Mountain, scattered occurrences have been found at small rock outcrop sites. At Mount Buckley, population is restricted to scattered areas of microhabitat on separate rock outcrop sites within an area of 0.5 acres (0.2 ha) in size. At Mount LeConte, research indicates that the healthiest of the surviving populations occur in four small, separate areas of rock outcrop sites.
HABITAT
Inhabit damp but well-drained moss and liverwort mats that grow on completely shaded rocks or boulders in mature, high-elevation coniferous (red spruce and Fraser fir) forests. Cannot tolerate extremes of moisture, and excessive gain or loss of moisture within body. The mats cannot be too dry (it is very sensitive to desiccation) or too wet (large drops of water can also pose a threat to it). As a result, it builds tube-shaped webs in interface between mat and rock surface (although sometimes extends into interior of mat) to control amount of moisture within surroundings. Tubes are thin-walled and typically broad and flattened with short side branches.
BEHAVIOR
Little information is known on its behavior.
FEEDING ECOLOGY AND DIET
Little information has been collected on feeding habits. No record of prey having been found in webs, nor has it been observed taking prey in the wild, but abundant springtails (tiny, wingless insects) in moss mats provide most likely source of food.
REPRODUCTIVE BIOLOGY
Little is known about its breeding habits, lifecycle, or life span.
CONSERVATION STATUS
Not listed by the IUCN. It is considered Endangered in its entire range by the U. S. Fish and Wildlife Service. It was listed as Endangered under the U. S. Endangered Species Act in February 1995, after research showed that its population size and distribution was limited to only four sites, with only one stable site left. Its populations are believed to be diminishing because of rapid decline of damp, high-elevation old-growth forest habitats (especially the Fraser fir); decline brought about by infestation of exotic insect (balsam wooly adelgid) that has been killing off fir and spruce trees, air pollution brought about by acid rain, and past land use.
SIGNIFICANCE TO HUMANS
Not known to be commercially valuable; however, because of its rarity, it is believed that collectors may seek it out.
