Ask any oysterman in Texas about the oyster drill and the response you get might be laced with expletives. Ask an oysterman in Louisiana about oyster drills and they will say the same thing...and then they will tell you how to cook them.
Oyster drills are a species of carnivorous snail against whom oystermen have been waging a war for well over a century on the Gulf Coast. This is because oyster drills love to eat oysters. Specifically, drills love to eat young oysters, called spats. The drill bores a hole through the thin shell of a young oyster and sucks the sweet innards out. A drill can bore through and eat about a spat a day. They move fast, and have a finely tuned sensory system perfectly equipped to find whatever food is available, including mussels, barnacles, detritus, and the aforementioned oyster.
All that aside, the oyster drill is still a snail. And, being a snail, the drill is delightful fare for the table. Happily for those of us who are lucky enough to live near the Gulf Coast, drills are plentiful and easy to find. They are not consistently found, but a solitary drill is rarely encountered. If you see one, chances are you will soon find enough, with a little patience, to provide a fine meal, if nothing else. The first picture shows the results of about 15 minutes' work in a good spot. Look for them in saltier areas of bays, around oyster reefs and on rocky areas. They are usually not found in very sandy areas.
Alas, though snails are eaten throughout the world, on all continents where they are found, very few Americans are these days familiar at all with the humble snail. Even most chefs are at a loss when presented with a live gastropod, which is not at all surprising, considering the only snail most chefs will see comes out of a can. Don't get me wrong- high quality canned snails exist, and they are a joy to eat, but they are still a far cry from the animal in situ. I have been very lucky, and have had many chances to cook, clean, and eat fresh snails- vineyard snails in Paris and Aix, rice field snails in Chiang Mai, Apple snails in Udon, marsh periwinkles, drills, and whelks in Texas and Louisiana. Let us not underestimate any snail.
What follows, with apologies to any who consider it elementary, is a bit of an introduction to the humble oyster drill. Most of the following comments apply to all snails- though our marsh periwinkles and other small snails do not require the same treatment to render them tender- though they certainly don't suffer from it.
First- a drill may not be cooked like a bi-valve. The edible part of the drill is the 'foot', which is used for locomotion and feeding. Hence, the muscle is quite strong, and the meat is consequently quite firm. Not tough, but certainly firm. A bit of further processing is necessary if you're looking for anything with a less crispy texture.
On the other hand, my wife has certainly done them right with just a quick boil in 'laab hoy'.
The edible portion may be extracted in one of two basic ways- raw or cooked. If you are looking for raw meat: one swift blow with a claw hammer will bust the shell. Pull out the whole animal. Pull off the large sac of guts. There will still be another section of gut which is attached to the head. Look for antennae (or small stubs) right at the base of the 'foot'. Slip your nail under the head, and pull toward the 'tail'. With a little practice, this piece is easily removed. The 'operculum' (the 'shell' on the 'foot') may be cut off with a knife. The picture shows whelk meat, but the idea is the same. I might recommend wearing gloves if you shell the drills raw. The drills secrete a chemical which, when exposed to oxygen, turns purple. Though it is completely harmless, it will stain hands for weeks (incidentally, it is a species closely related to drills that was used in the ancient Mediterranean world in the production of a fabulously expensive cloth dye).
Otherwise, you may extract the meat after cooked. Blanch the snails for 10-15 minutes in salted water. When the operculums start falling off, the snails are ready. Let them cool, then pull the meat out with a toothpick. Pull off all the organs just as you would for raw snails.
Now, what does one do with snails? Raw, they may be pounded then fried or grilled; they very good ground and used in chowders or stuffings. At our house, drill fritters with a pungent dipping sauce are a consistent hit. Large drills are just barely big enough to be pounded into very small 'drill steaks'. Blanched meat may be used in soups, braised with garlic (with stunning results), tossed into salads, pickled, preserved, and simply eaten with a good drawn butter and salt. Or just throw the live snails in a curry, cook for about 20 minutes, and pick the meat out of the shells at the table.
There are undoubtedly dozen of ways to cook oyster drills that are even better than what I've mentioned here. Find out some of them for yourself. Enjoy.