Carychium nannodes
File thorn

Key Characteristics

The file thorn is a land snail characterized by a minute (to .06 inches long), elongate, smooth, translucent white shell with 4-5 whorls. The body is whitish with the head featuring a snout-like protuberance and eyes located at the base of stout tentacles.

Status and Rank

  • State Status: SC
  • State Rank: SNR
  • Global Rank: G5


County NameNumber of OccurrencesYear Last Observed
Distribution map for Carychium nannodes

Updated 5/15/2018. Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.


The file thorn prefers the mesic wooded areas of carbonate cliffs and floodplains (Nekola 2009).

Natural Community Types


For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.

Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.


An Ontario file thorn population suffered serious negative impacts after extensive recreational rock climbing altered its limestone cliff habitat (McMillan et al. 2003). Protecting sections of such habitat  from recreational overuse will benefit this and many other vulnerable plant and invertebrate species that depend upon the unique ecosystem of carbonate cliffs. Other factors that may contribute to the loss of file thorn habitat include quarrying and road construction (Nekola 2009). Further research into the distribution and specific site preferences of this species are needed before effective management can be implemented.

Active Period

Breeding from first week of May to fourth week of June

Survey Methods

As visual detection of this species is difficult, specimens are collected by litter sampling in suitable habitat. Samples are thoroughly heat-dried, soaked in water for a number of hours to separate the various components, and finally passed through a series of sieves. The shells are then able to be hand-picked from the remaining sample material (Nekola 2003).

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at [Accessed Sep 23, 2018]


Survey References

Technical References

Facebook link