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North Dakota's

Federally Listed Endangered, Threatened, and Candidate Species – 1995


Callused Vertigo (Vertigo arthuri)

GIF -- species photo gif--species map

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Status: Former Candidate (Note: As of February 28, 1996, this species is no longer listed as a Candidate species. However, it remains a species of management concern.)

Historical Status:
Arthur Krause collected the first two callused vertigos from river drift on the Little Missouri River near Medora, North Dakota. Originally identified as Vertigo bollesiana Var. arthuri until 1882 when Van Martens renamed the species Vertigo arthuri. The callused vertigo has never been extremely abundant, but localized populations have existed. The species dispersal is restricted because of its physical nature and narrow geographic distribution which is enclosed by the south border of the Northern Province in the eastern U.S. and the endemic Rocky Mountain Province in the west.

Present Status:
Populations of the callused vertigo exist in the Black Hills of South Dakota and Bear Lodge Mountains of Wyoming. The callused vertigo has also been collected sparingly in North Dakota and Minnesota, and in other areas of South Dakota and Wyoming.

Habitat:
The callused vertigo is found in moist, undisturbed forested areas. Callused vertigo prefers habitat comprised of diverse flora with a varied understory and deep litter, positioned on shaded north-facing slopes, normally at the base or extending slightly onto the adjacent floodplain. The callused vertigo is generally found on limestone or schist substrate. The species occurs most frequently in sites with high mollusc diversity.

Life History:
Little information is known about the callused vertigo's specific reproductive process and daily and seasonal movements, but it's believed to be similar to related vertigo species. The callused vertigo's feeding habits are cryptic, it feeds on the surfaces of half-decayed leaves.

Aid to identification:
The callused vertigo has a dark orange/brown shell. The shell is cylindric in form with 4 3/4 moderately convex whorls. The callused vertigo has an average length of 1/2 inch, and a diameter of 1/3 inch. The outer lip is very heavily calloused. A small aperture (opening in shell) is somewhat pear shaped.

Reasons for decline:
The callused vertigo is highly sensitive to habitat disturbances and pollution levels. The activities of logging, intensive grazing, and trampling of habitat have been particularly harmful to the species habitat. These activities decrease floral diversity, open the canopy, and increase isolation.

Comments:
The callused vertigo is a land snail.

References:
How to Know the Eastern Land Snails, by J. B. Burch, 1962. Published by WM. C. Brown Company Publishers, Dubuque, Iowa. Land Snail Survey of the Black Hills National Forest, South Dakota and Wyoming. by T.J. Frest and E.J. Johannes, 1993. Final report to the U.S. Forest Service, Black Hills National Forest, and the U.S. Fish and Wildlife Service, South Dakota State Office.


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