Spruce-fir moss spider

Spruce-fir moss spider
Conservation status
Endangered (ESA)
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Arachnida
Order:	Araneae
Family:	Dipluridae
Genus:	Microhexura
Species:	M. montivaga
Binomial name
Microhexura montivaga Crosby & Bishop, 1925

The Spruce-fir moss spider, Microhexura montivaga, is an endangered species of spider found at high elevations in the southern Appalachian Mountains. First identified in 1923, they inhabit moss that grows on rocks underneath the forest canopy.

Description

This is one of the smallest mygalomorph spiders, with adults only measuring 3 to 4 mm. The coloration varies from light brown to yellow-brown to a darker reddish brown, with no markings on its abdomen. Their chelicerae project forward, and one pair of spinnerets is very long. They possess a second pair of book lungs, which appear as light patches behind the genital furrow.^[1]

Biology

They construct tube-shaped webs, apparently for shelter, for prey has never been found in them. They probably feed on the springtails that are abundant in the moss mats.^[1] The spiders can take as long as three years to reach maturity, due to the low temperatures and resulting slow metabolism.

Endangered status

The widespread death of Fraser fir trees has destroyed many habitats for the spiders, and they were listed as endangered in 1995. Many Fraser firs have died due to infestation with Adelges piceae, the balsam wooly adelgid, an insect pest introduced from Europe. The resulting thinning of the forest canopy leads to the drying of the moss mats that are essential for the spider's survival, as it requires climates of high and constant humidity.^[1]

Distribution

This spider is known from Fraser fir and red spruce forests on mountain peaks at and above 1,650 m in the Southern Appalachian Mountains of North Carolina and Tennessee. They have been recorded from Clingmans Dome and Mount Collins (both very small populations), Mount Le Conte, Mount Mitchell (probably extirpated), Grandfather Mountain, and Roan Mountain.

The Tennessee population, located in Sevier County, was considered healthy up to 1989, but is now possibly extirpated. On two locations in North Carolina, there was only one spider found each in recent years. Only the population along the Avery/Caldwell County line in North Carolina seems to be relatively stable. This population appears to be restricted to the moss mats on a single rock outcrop and a few surrounding boulders.^[1]

Footnotes

1. ^ ^{a b c d} US Fish & Wildlife Service

References

• US Fish and Wildlife Service: Spruce-fir moss spider
• US Fish and Wildlife Service: Spruce-fir Moss Spider in North Carolina
• Platnick, Norman I. (2009): The world spider catalog, version 9.5. American Museum of Natural History.