The spruce-fir moss spider (''Microhexura montivaga'') is an

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...

spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...

found at high elevations in the southern

Appalachian Mountains The Appalachian Mountains, often called the Appalachians, are a mountain range in eastern to northeastern North America. The term "Appalachian" refers to several different regions associated with the mountain range, and its surrounding terrain ...

. First identified in 1923, it inhabits

moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...

that grows on rocks underneath the forest

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an a ...

Description

''M. montivaga'' is one of the smallest

mygalomorph The Mygalomorphae, or mygalomorphs, are an infraorder of spiders, and comprise one of three major groups of living spiders with over 3,000 species, found on all continents except Antarctica. Many members are known as trapdoor spiders due to t ...

spiders, with adults measuring only 3 to 4 mm (about 1/8 inch). The coloration varies from light brown to yellow-brown to a darker reddish brown, with no markings on the abdomen. The

chelicerae The chelicerae () are the arthropod mouthparts, mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated ...

project forward, and one pair of

spinneret A spinneret is a silk-spinning organ of a spider or the larva of an insect. Some adult insects also have spinnerets, such as those borne on the forelegs of Embioptera. Spinnerets are usually on the underside of a spider's opisthosoma, and ar ...

s is very long. It possesses a second pair of book lungs, which appear as light patches behind the genital furrow.

Distribution and habitat

''M. multivaga'' is known from Fraser fir and red spruce forests on mountain peaks at and above in the Southern Appalachian Mountains of

North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...

Virginia Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...

and

Tennessee Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...

. It has been recorded from

Kuwohi Kuwohi (, also known as Clingmans Dome, its former official name) is a mountain in the Great Smoky Mountains of Tennessee and North Carolina in the Southeastern United States. At an topographical summit, elevation of , it is the highest mountai ...

and Mount Collins (both very small populations), Mount Le Conte,

Mount Mitchell Mount Mitchell (''Attakulla'' in Cherokee) is the highest peak of the Appalachian Mountains and the highest peak in mainland North America east of the Mississippi River. It is located near Burnsville in Yancey County, North Carolina in the B ...

(where probably

extirpated Local extinction, also extirpation, is the termination of a species (or other taxon) in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinctions. Local extinctions mark a chan ...

Grandfather Mountain Grandfather Mountain is a mountain, a non-profit attraction, and a North Carolina List of North Carolina state parks, state park near Linville, North Carolina. At 5,946 feet (1,812 m), it is the highest peak on the eastern escarpment of the Blu ...

, 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. The Fraser fir and

red spruce ''Picea rubens'', commonly known as red spruce, is a species of spruce native to eastern North America, ranging from eastern Quebec and Nova Scotia, west to the Adirondack Mountains and south through New England along the Appalachians to wester ...

, which are

Ice Age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...

relics, dominate the forests that grow on these summits. On the damp, cold forest floor, bryophytes like

mosses Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta ('' sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and ho ...

and

liverworts Liverworts are a group of non-vascular plant, non-vascular embryophyte, land plants forming the division Marchantiophyta (). They may also be referred to as hepatics. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in wh ...

are widespread, and the threatened spruce-fir moss spider lives in

bryophyte Bryophytes () are a group of embryophyte, land plants (embryophytes), sometimes treated as a taxonomic Division (taxonomy), division referred to as Bryophyta ''Sensu#Common qualifiers, sensu lato'', that contains three groups of non-vascular pla ...

matting that form on rocks and have a very specific combination of moisture and thickness. 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. These spiders have survived in temperatures that range between -17.8 °C or 0 °F and 19.8 °C or 67.6 °F within mountainous regions of the Southern Appalachians.

Biology

''M. montivaga'' constructs tube-shaped webs, apparently for shelter, as prey has never been found in them. It probably feeds on

springtail Springtails (class Collembola) form the largest of the three lineages of modern Hexapoda, hexapods that are no longer considered insects. Although the three lineages are sometimes grouped together in a class called Entognatha because they have in ...

s that are abundant in moss mats. Scientists know that spiders play a significant role in controlling insect populations as top predators and that the extinction of one species could ripple impact on other spider species and ecosystems. The spruce-fir moss spider, which likely consumes mites and springtails, is the

top predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...

in its

microhabitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

. ''M. montivaga'' can take as long as three years to reach maturity, due to low temperatures and resulting slow

metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

Endangered status

The widespread death of

Fraser fir The Fraser fir (''Abies fraseri''), sometimes spelled Frasier fir, is an endangered species of fir native to the Appalachian Mountains of the southeastern United States. They are endemic to only seven montane regions in the Appalachian Mountains ...

trees has destroyed many habitats for ''M. montivaga'', and the spider species was listed as endangered in 1995. Many Fraser firs have died due to infestation with ''

Adelges piceae The balsam woolly adelgid (''Adelges piceae'') is small wingless insect that infests and kills firs. In their native Europe they are a minor parasite on silver fir and Sicilian fir, but they have become a threat especially to balsam fir and ...

'', the balsam woolly adelgid, an

insect pest Economic entomology is a field of entomology, which involves the study of insects that benefit or harm humans, domestic animals, and crops. Insects that pose disadvantages are considered pests. Some species can cause indirect damage by spreading di ...

introduced from

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

NatureServe NatureServe, Inc. is a non-profit organization based in Arlington County, Virginia, United States, US, that provides proprietary wildlife conservation-related data, tools, and services to private and government clients, partner organizations, and ...

considers the species "''Imperiled''".

Description

Distribution and habitat

Biology

Endangered status

References

External links

Further reading