Virginia Land Snails
Photo(s): Mesodon thyroidus by Bill Frank ©, views of its shell by Larry Watrous ©.
Click photo(s) to enlarge.
Mesodon thyroidus (Say, 1816)
Common name: White-lip Globe
Width: 17-28 mm
Height: 11-18 mm
This snail’s rounded shell is a bit smaller and thinner than the largest Polygyrids, and it has a unique umbilicus. Its reflected lip partly covers this opening, leaving a slit-like gap. It often has a small parietal tooth, but this tooth is sometimes absent, even within entire populations (which we believe have been mistakenly named the spurious Mesodon clausus), so it is a poor character for identification.
M. thyroidus can be patchy in occurrence, found on richer soils at lower elevations along river floodplains, wetlands, and limestone ledges. It is occasionally found in cultivated gardens and in meadows (Hubricht, 1985), and is believed to eat mainly fungi (Wolf & Wolf, 1939). In Virginia this species was found in various oak and maple habitats (Burch, 1956).
In Illinois, overwintering M. thyroidus developed a relatively thin and clear epiphragm, and oriented aperture-up, partially buried in soil (Blinn, 1963). They became active during brief periods of warm weather. Summer activity of this species was in the vicinity of fragmented log mold. Most individuals matured in two years. The growth of immature M. thyroidus was suppressed by adults of the same species in a field cage experiment, apparently through resource competition (Pearce, 1997).
Synonyms for this species include Helix thyroidus, H. thyroides, H. t. var. pulchella, Mesodon leucodon, M. thyroides, Polygyra thyroidus, and P. thyroides.
Mesodon thyroidus is widely distributed in the south, midwestern and eastern United States. It is found in most Virginia counties.
NatureServe Global Rank: G5
NatureServe State Rank: S5
Ken Hotopp, Meegan Winslow 9/2012Range Map