Guide

Look closerInsects

Which way a snail shell coils

April to November

Hold an empty land-snail shell with its tip up and the opening facing you. In the northeastern states the opening is almost always on the right, though small pond snails of the Physa family are the exception and coil to the left.

Why this time of year

Scraping the leaf litter aside at the base of a tree, a stump or a stone wall turns up both small and large land snails and their shells.

How to notice it

  1. Look for empty shells in leaf litter, at the foot of a stone wall, or under a loose slab of bark, and brush the litter aside gently with a finger.
  2. Pick up one shell, point the tip up and turn the opening toward you. Note whether the opening is on your right or your left.
  3. Check a few more land-snail shells from the same spot. Expect every one to have the opening on the right. A left-opening shell picked up at a pond edge is likely a Physa pond snail, which coils that way as a rule.
  4. Put each shell back where you found it. Many of the snails here are very small, so a hand lens helps.

Try this with kids: Tip pointing up, opening facing you: is the hole on your right hand or your left? Did you find any left ones?

Word to know: “Dextral” means the opening sits on the right when the shell is held tip-up and facing you; sinistral means it sits on the left.

Safety

  • Wash hands after handling shells and litter.
  • Put shells back; live snails and fresh shells should be left alone.

Sources

  • pmc.ncbi.nlm.nih.govPeer-reviewed paper on chirality in terrestrial pulmonates: 'In North America (north of Mexico), 99.4% of the 689 species are dextral and 0.6% are sinistral'; names the 4 sinistral NA land species (Gastrocopta perversa; Pupilla nefas, P. sinistra, P. syngenes); Clausiliidae not represented in North America. Species counts, not individual shells.
  • prod.lsa.umich.eduGetz, Chichester and Burch 2017, Malacological Review: key to northeastern US and SE Canada land snails (about 75 native, 20 introduced species); scraping litter at tree bases, stumps and stone walls exposes small and large species; most northeastern snails are very small. No left-coiling species described.
  • sci.muni.czNekola and Coles 2010, Amer. Malac. Bull.: keys to the 65 pupillid species east of the Rockies do not include any of the 4 sinistral NA land species.
  • hbs.bishopmuseum.orgBishop Museum Occasional Papers 2019: Clausiliidae (left-coiling door snails) notably absent from North America.
  • animaldiversity.orgU Michigan Animal Diversity Web: freshwater Physidae are sinistral (left-handed).
  • theconversation.comAngus Davison (U Nottingham): lefty shells in garden snails usually come from a developmental accident, not inheritance.
  • shellmuseum.orgBailey-Matthews National Shell Museum: most coil right-handed; with the tip pointing up the opening is on the right side.

Checked against these sources on October 6, 2026.

In the guide for April, May, June, July, August, September, October, November

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