Eastern mud snails are super smellers.
If the nose knows, these marine gastropods might be out of luck. Fortunately for these schnoz-less sensations, the tentacles tell all. As their main chemoreceptor structure, mud snail tentacles serve as olfactory organs that provide many felicitous functions.
The top of the head tentacles must be keenly attuned to their environment. Finding food through prey detection, avoiding predators, following their friends and coming together in breeding aggregations are all accomplished with help from these and other internal sensing structures.
What mud snails smell, or actually detect, are pheromones or chemical signals that they (and others) emit. Eastern mud snails, also called mud dogwhelks, perform their sensory skills in Island waters.
Find these slight sliders in tidepools, marshes, ponds and other shallow marine areas where they crawl and coexist. Small and harmless, mud snails can be easily collected and observed. While they are an oft-seen snail, it was a mass of miniature egg cases that led to this conversation of a curious creature’s sensory style.
On a pond beach last week, I came across that unusual collection of egg cases. Hundreds of petit gem-like cases covered fingerlike weedy-looking strands, and though vaguely familiar, it took some research and outreach to match the animal to its baby-carrying container.
Shelley Edmundson, PhD and executive director of the Martha’s Vineyard Fisherman’s Preservation Trust, confirmed my initial identification of eggs of Ilyanassa obsoleta, the aforementioned mud snail, and shared some interesting observations of these egg cases. She noted that she sees them a lot on large whelk shells she studied, and in whelk traps.
There is a compelling reason that she finds them there, one that ties the creatures together, and provides yet another important function of those pheromone-detecting tentacles.
When mud snails are on the prowl for procreation, they come together through chemical connections. Up to thousands of snails detect each other’s pheromones and form breeding aggregations. Sexes are separate, so there are male and female mud snails out there looking for love. Attracted by the pheromones all are putting out, this gathering facilitates them finding each other.
Mating occurs and fertilization happens internally. The female then produces up to 150 fertilized eggs in rubbery capsules that need a hard substrate for attachment.
Pheromones are not only for finding love, but also for finding a place to settle their young. Researchers have noted and documented mud snail attraction to the pheromones of other marine species, specifically oysters, whelks and parchment worms. Snails follow the chemical signals of those creatures too.
The mud snails are not confused or looking for a cross-species love affair; they simply need a substrate on which to attach their eggs. One that is elevated off of the sea floor where sedimentation could smother developing embryos. This explains Shelley’s observations of the cases on whelk shells and my observation of the eggs on what I now believe were parchment worm casings.
The egg cases will hatch planktonic (free-floating) larvae, called veligers, which will eventually settle and develop into the small, gray motile mud snails that are a more familiar form (to us, at least).
While this all may sound like a wild animal adventure that we may never truly understand, it is gastropod logic that makes nearly perfect scents to the mud snails.
Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown, and author of Martha’s Vineyard: A Field Guide to Island Nature and The Nature of Martha’s Vineyard.
This article appears in May 29, 2026.