Susan J. Hewitt Curator

I am a serious amateur or semi-professional malacologist, originally from Britain. I live in Manhattan, in NYC. I have had 47 scientific papers published so far. I am interested in both marine and non-marine Mollusca, the ones that have shells, and the ones without shells. :) I joined iNaturalist in September 2014. My forté is identifying mollusks, but I do also have a little general natural history knowledge. I am currently learning to ID the spontaneous vegetation of NYC, and I am attempting to record the overall biodiversity of Randall's Island/Wards Island in Manhattan. Some people call me the snail lady or the shell lady.

In June 2015, I went on a 3-week marine expedition to the Dutch Caribbean island of Sint Eustatius (I am still writing up the results!), and two weeks before the expedition started, I was away for a month in Nevis, another small island south of there. In 2016, I was on Nevis for the month of May; in Southern California for three weeks in September; and on Sanibel in SW Florida for two weeks in mid December. In 2017, I enjoyed, or will enjoy, three similar trips.

I have learned to identify: the non-marine (and marine) mollusks of the British Isles (especially East Anglia); the marine mollusks of the West Coast of North America (especially San Diego); and the marine mollusks of the East Coast of the USA (especially NY State); the Gulf of Mexico (especially Sanibel, Lee County, Florida); and the Caribbean Sea (Nevis, St. Kitts, St. Eustatius, and Montserrat).

I taught a college seminar at Yale on mollusks. I worked for two years at the Louis Agassiz Museum of Comparative Zoology, at Harvard, in the mollusk department. I volunteered many years at the American Museum of Natural History, in the malacology section of Invertebrate Zoology, and in the invertebrate section of Paleontology. I am now a Volunteer Emeritus at AMNH.

I have given material to numerous museums in the US and the UK. I did a great deal of fieldwork mapping the distribution of the land and freshwater mollusks of the British Isles, for the two published Atlases edited by Michael P. Kerney.

On Wikipedia, I started editing in 2007, under the screen name Invertzoo, and I was extremely active on there for several years. In 2011, my face and words were used online in a world-wide fundraising Wikipedia banner, and as a result of that, I was interviewed in print, online, and in the broadcast media.

Currently I am trying to recognize and identify the native non-marine mollusks of the US, a huge task. I already understand most of New York City's non-marine species, the majority of which are introduced from Europe.

NOTE: I don't know the native non-marine mollusks of other areas in the world, such as, for example, New Zealand. However, I can probably recognize most of the European species that have been accidentally introduced there, and to so many other places all over the world.

ANOTHER NOTE: I changed my screen name here to my real name on September 23, 2016. Previously my screen name on here was "Invertzoo" -- I still use that name on Wikipedia.


I enjoy trying to identify mollusk species from the faunal zones that I know well, however, ID-ing mollusks from photos is often very difficult indeed, so I wrote these guidelines:


*** SCALE OBJECT -- In one photo please include a scale object (e.g. your fingertip or finger(s), a pen or pencil, a coin, or ideally, a small ruler). Without this, it can be hard for anyone else to guess the real size of the creature, which strongly affects the possible ID. If you pose a shell on your hand, the scale is automatically built-in:

*** SHELLED MOLLUSKS -- if the animal is alive, look around the immediate area and see if you can find an empty (full-grown) shell that is as fresh as possible. Using an empty shell (and sometimes even using a live animal), it is often not difficult to shoot three views from different angles (dorsal, ventral and lateral), including showing details of the aperture or the interior of the shell if it's a bivalve. Failing this, don't be shy to pick up the creature and turn it around this way and that for photographing. When you are done, put it back where it was, or nearby in a damp and safe place, with the aperture down.


*** With empty gastropod shells as well as live snails, please shoot more than one view, ideally three: dorsal, ventral, and lateral. At least photograph both the dorsal surface and a clear view of the aperture. If you can't find an empty shell, most live snails will retract if you prod them, and then you can get a shot showing the shape of the aperture, the nature of the operculum (in species that have one) and the color of the lip of the shell, where present.


*** Land snails:

If you find a group of snails that look more or less the same, always pick out whichever snail in the group has a relatively large shell where the edge of the aperture is sturdy and reinforced. That means it's an adult.

Juveniles can be almost as big as an adult, but the lip of their shell is very soft and still growing. We need to see a fully adult shell its a reinforced lip in order to see the characteristics that give rise to a reliable ID.

Even a dead empty adult shell is good for ID-ing the species, especially if the empty shell is fairly fresh still and not too bleached out.

Check these examples for the right ways to photograph a land snail shell:

*** Land slugs. One shot from above is often not enough to ID a slug. We usually need at least one additional close shot from the side. If possible, photograph the right side of the slug, which will show the position of the respiratory pore, and the markings around it. A scale object is almost always necessary.

Sometimes we need to see the shape of the tip of the tail of the slug, from the side. We also may need to be able to see the color and markings on the foot fringe, where the foot meets the substrate. The color of the sole of the foot of the slug is also often helpful to know (is it orange? white? longitudinally banded?) so please gently turn the slug over. The qualities of the body mucus (orange? colorless? milky when irritated? thick and sticky?) are also often helpful to know.

If a slug is contracted (or if a land snail is retracted) just pour a little water from your water bottle over it and wait a minute; it will become active and extended.


*** Bivalves, whole or single valves? Please shoot the exterior square-on, NOT at an angle, and for empty valves, please shoot the interior too, square-on and in enough detail that we can see the hinge line. If the bivalve is very generic-looking, a lateral shot is also a good idea because it shows the three-dimensional shape of the shell.

*** Limpets? If possible, find an individual where the shell is is good condition (not eroded) with the sculpture intact. If you have an empty shell, photograph the outside, inside and a side shot. Remember that limpets can be very variable, so an image of just one individual in a population may sometimes not be enough to ID the species.

*** Chitons? Try to get some close shots of an individual where the shell valves are not too eroded or encrusted. We need to see the sculpture of the plates and the kind of girdle the chiton has.

*** Sea hares and sea slugs? Try as much as possible to photograph these while they are in water; out of the water their shape tends to collapse into a blob.



Land snails and slugs can leave behind them four kinds of tracks, trails or signs:

1. Shiny silvery dried mucus trails where they have moved along, often at night.

2. Grazing trails are left usually by slugs, but also by snails, on surfaces where they have fed on microscopic algae. These surfaces include tree bark as well as smooth human-made surfaces such as plastic, the glass of greenhouses, etc, as long as there are microscopic algae growing there.

3. Where land snails have rested for a while and then moved on, they often leave a small pile of poop behind.

4. Where snails have waited out dry weather ("estivation") waiting for the next rain shower or a watering event, they often leave behind flimsy broken remnants of an "epiphragm" -- a thin dried mucus layer that covers the aperture of the snail's shell. A snail secretes an epiphragm to prevent it from losing too much moisture while it remains motionless and withdrawn in to the shell during the dry period.

P.S. Do wash your hands before you eat lunch after handling land snails and land slugs; some carry parasites that can spread to humans.

P.P.S. Marine shells that are damaged and beach-worn may sometimes be impossible to ID to species, as may some other shells, and even some live animals.

P.P.P.S. There are approximately 100,000 species of mollusk worldwide, not counting the as yet unnamed species. No single person can identify more than a few thousand mollusks to species from memory.

Note: Even though I try to be conscientious, I do inevitably get some IDs wrong, especially because on iNaturalist I am always learning something new, and pushing the boundaries of what I understand, or what I think I understand. Please always feel free to put in a new ID, or to quiz me about an old one if you think it might be incorrect. Live and learn! :)

View all

Member of the iNaturalist Network   |   Powered by iNaturalist open source software