Vertigo modesta (Cross Vertigo)




Vertigo modesta is a terrestrial snail that is found over a very large region.  Vertigo modesta been found to range from Maine to California and south to New Mexico, Arizona, and Texas in the United States, and reaching from Ontario to British Columbia in Canada (Lee, 2007).  This species has even been found throughout Europe, present in Britain and Andorra as well as Norway, Finland, Sweden, Switzerland, Bavaria, and Iceland (Forsyth, 2002).

The environment is characterized by a couple of key components.  It is important that the environment contain adequate moisture, a rich food supply, shelter for the animal, as well as a source for calcium; these being important for all land snails.  Moisture is important for the snail, not only enabling the physiological processes that are necessary for life but also enabling locomotion, as the mucus produced for movement is composed mostly of water.  The availability of shelter is extremely important for all land snails as it provides protection for the snail from extreme weather conditions as well as from predators  (which includes a vast array of birds, small mammals, reptiles, amphibians, and even other snails and slugs).  A calcium source is crucial for the snail as, the calcium is necessary for the snail to maintain its shell.   Because of this, habitats can often be found in areas of abundant limestone, or areas with a high concentration of calcium carbonate in the soil.  Snails can still occupy a habitat lacking this calcium-rich soil as long as the surrounding vegetation can provide sufficient amounts of calcium (Lee, 2007).

Vertigo modesta specifically, tolerates a generally cooler climate in comparison to other land snails.  When this species was found in Britain, it was found in a very severe climate and it is thought that the species may be restricted to only those rigorous environments (Marriot, 2000).  There have been populations found in Northeastern Wisconsin where the species lived under very large, glacially deposited boulders that would insulate the snails against the warmth of summer, and allowing ice to persist much longer than usual, lasting through June (Nekola, 2003).  There has also been a subspecies; Vertigo modesta parietalis that has been closely observed in Michigan.  This subspecies lives at the base of a basalt cliff on open talus slopes.  In this area cool air can seep in and keep the habitat cool and moist, perfect for this species.  The soil in this area is organic-rich and many ferns also occupy the area.  This same subspecies found in Minnesota once again inhabits the talus slopes, but here shares the area with lichens and moss and is canopied by mature trees consisting of eastern white pine (Pinus strobus), white spruce (Picea glauca), and northern white-cedar (Thuja occidentalis) (Lee, 2007).  Another subspecies, Vertigo modesta arctica, was found in the high altitude, mountainous region of Andorra.  At this site all of the Vertigo modesta arctica were found on a small area of unshaded and exposed slope that was herb-rich and had an abundance of small streams that provide plenty of calcium carbonate (Holyoak, 2004).