Spruce-fir moss spider
Encyclopedia
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
.
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.
, apparently for shelter, for prey has never been found in them. They probably feed on the springtail
s that are abundant in the moss mats. The spiders can take as long as three years to reach maturity, due to the low temperatures and resulting slow metabolism
.
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.
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.
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
of spider
Spider
Spiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
found at high elevations in the southern Appalachian Mountains
Appalachian Mountains
The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...
. First identified in 1923, they inhabit moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
that grows on rocks underneath the forest canopy
Canopy (forest)
In biology, the canopy is the aboveground portion of a plant community or crop, formed by plant crowns.For forests, canopy also refers to the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms .Sometimes the term canopy is used to refer to the extent...
.
Description
This is one of the smallest mygalomorphMygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...
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
Chelicerae
The chelicerae are mouthparts of the Chelicerata, an arthropod subphylum that includes arachnids, Merostomata , and Pycnogonida . Chelicerae are pointed appendages which are used to grasp food, and are found in place of the chewing mandibles most other arthropods have...
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.
Biology
They construct tube-shaped websSpider web
A spider web, spiderweb, spider's web or cobweb is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets....
, apparently for shelter, for prey has never been found in them. They probably feed on the springtail
Springtail
Springtails form the largest of the three lineages of modern hexapods that are no longer considered insects...
s that are abundant in the moss mats. The spiders can take as long as three years to reach maturity, due to the low temperatures and resulting slow metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
.
Endangered status
The widespread death of Fraser firFraser Fir
Abies fraseri is a species of fir native to the mountains of the eastern United States. It is closely related to Abies balsamea , of which it has occasionally been treated as a subspecies or a variety Abies fraseri (Fraser fir) is a species of fir native to the mountains of the eastern United...
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
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
from Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. 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.
Distribution
This spider is known from Fraser fir and red spruce forestsSouthern Appalachian spruce-fir forest
The Southern Appalachian spruce-fir forest is a type of montane coniferous forest that grows in the highest elevations in the southern Appalachian Mountains of the eastern United States...
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
Clingmans Dome
Clingmans Dome is a mountain in the Great Smoky Mountains of Tennessee and North Carolina, in the southeastern United States. At an elevation of , it is the highest mountain in the Smokies, the highest point in the state of Tennessee, and the highest point along the Appalachian Trail...
and Mount Collins
Mount Collins
Mount Collins is a mountain in the Great Smoky Mountains, located in the Southeastern United States. It has an elevation of above sea level. Located along the Appalachian Trail between Clingmans Dome and Newfound Gap, the mountain is a popular destination for thru-hikers. A backcountry shelter...
(both very small populations), Mount Le Conte, Mount Mitchell
Mount Mitchell (North Carolina)
Mount Mitchell is the highest peak of the Appalachian Mountains and the highest peak in the eastern United States. It was the highest point in any state of the United States until Texas joined the union in 1845. The nearest higher point east of the Rocky Mountains is Harney Peak in the Black Hills...
(probably extirpated), Grandfather Mountain
Grandfather Mountain
Grandfather Mountain is a mountain, a non-profit attraction, and a North Carolina state parknear Linville, North Carolina. At 5,946 feet , it is the highest peak on the eastern escarpment of the Blue Ridge Mountains, one of the major chains of the Appalachian Mountains. The Blue Ridge Parkway...
, and Roan Mountain
Roan Mountain (Roan Highlands)
Roan Mountain is the highpoint of the Roan-Unaka Range of the Southern Appalachian Mountains, located in the Southeastern United States. The mountain is clad in a dense stand of Southern Appalachian spruce-fir forest, and includes the world's largest natural rhododendron garden, and the longest...
.
The Tennessee population, located in Sevier County
Sevier County, Tennessee
Sevier County is a county of the state of Tennessee, United States. Its population was 71,170 at the 2000 United States Census. It is included in the Sevierville, Tennessee, Micropolitan Statistical Area, which is included in the Knoxville-Sevierville-La Follette, TN Combined Statistical Area. The...
, was considered healthy up to 1989, but is now possibly extirpated. On two locations in North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
, 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.