September 25, 2015
There is a new citizen science project in town and we need your help to document the snails and slugs that call Los Angeles home. SLIME (Snails and Slugs Living in Metropolitan Environments) kicked off earlier this year, and we are already making some interesting discoveries about life in L.A.'s slow lane.
There are about a dozen common land snails in Los Angeles County. If you’ve hiked within the Palos Verdes peninsula, or up to the Baldwin Hills Scenic overlook you’ve probably seen two of the most common snails in urban Southern California. Like most Angelenos, they thrive in a Mediterranean climate and, in fact, ARE from a Mediterranean climate. The white Italian snail (Theba pisana) and milk snail (Otala lactea), hail from Southern Europe and reproduce abundantly in our neighborhoods, their adopted home. They are often found clustered on the same plant stem, sprinkler, sign, or fence, and in numbers from the dozens to hundreds.
Despite this presence, and close proximity to people in Los Angeles parks and along hiking trails, they are often confused for each other or misidentified as other species. Here's why.
Both are highly variable in color and in pattern. The next time you seen a bunch of them, take a close look. In white Italian snails, shell color can range from white to tan with varying degrees of banding, zigzags, and stripes of variable thickness.
Likewise, the milk snail’s shell can range from almost totally white to heavily banded with brown and tan stripes, which can be solid or stippled. And, to add to the confusion of the casual snail-watcher, these species sometimes overlap in habitat, as in the gardens of the White Point Nature Center in San Pedro.
So how do you tell the difference?
The white Italian snail (Theba pisana) is the smaller of the two species and at maturity is about the size of a dime. As an adult, its umbilicus, or the center of the underside of the shell, is partially covered by the lip of the shell.
The milk snail (Otala lactea) is the larger of the two species and about the size of a quarter at maturity. As an adult its umbilicus and part of the underside of the shell is glossy and brown in color.
Such confusion is not limited to sizable snails you’d find hiking, but makes distinguishing two tiny Los Angeles snails tricky as well. If you look under rocks, among leaf litter, or in the soil of potted plants, you might find two more snail doppelgangers: the orchid snail (Zonitoides arboreus) and the glass snail (Oxychilus sp.). They share the same two-toned gray-colored bodies, and flattened amber-colored shell, but can be distinguished by size and subtle differences in the shell.
When in doubt, which is most of the time even for seasoned snail observers, the best way to photograph a snail for identification is to take images of the shell from three different angles; the top (apical view), the side (apertural view), and the bottom (umbilical view).
So next time you find a snail (or slug for that matter) take pictures and send them into the SLIME project. You can submit them directly to iNaturalist, e-mail them to firstname.lastname@example.org, or tag them #natureinLA on social media. Either way, you will be able to put your new-found snail identification skills to the test, and I might get to help with the tricky taxonomy of terrestrial molluscs.