"Fiddlehead fern" is a bit of a misnomer. Several species of ferns have edible fiddleheads. The word "fiddlehead" (sometimes "fiddleneck") refers to the distinctive look of an unfurled frond, which can resemble the scroll of a violin. Most commonly the term "fiddlehead fern" refers to an ostrich fern, matteuccia struthiopteris, as these ferns yield some of the tastiest and most edible fiddleheads.
Search in cool, wet areas that have acidic soil, don't get a lot of sunlight, and are not prone to frosts.
Look for the general structure of an ostrich fern. As the name suggests, the sterile fronds of this plant somewhat resemble the neck of an ostrich, curling at the top like an ostrich's head. More generally, they slope gently outward from a narrow base. These fronds, which are deciduous, can reach a height of 4 to 6 feet and a width of 2 to 3 feet. The fertile fronds are brown and much shorter; they survive the winter but die the next year. They are feathery in their appearance.
Look for a smooth stem with a horseshoe shape reminiscent of a celery stalk. If you look very closely, you can see fine white hairs on the stem. The smooth stem is one of the more distinctive features of an ostrich fern.
Look for fiddleheads that are roughly 1 inch in diameter and are covered by a brown, papery layer of scales. The covering is also distinctive; many similar ferns have casing that is hairy, tough or difficult to remove.
Don't take all the fiddleheads--take just one or two per cluster. Leave the rest to grow up. The younger the fiddlehead is, the better it is to eat. Once the papery layer of scales has fallen off, leaving a beautiful, feathery coil behind, the fiddlehead is starting to get too old to eat--it will become tougher and more bitter. If you're not sure that you're dealing with an ostrich fern, take a sample to a botanist or wait to inspect the fern when it is mature, and then return the following spring to harvest the fiddleheads.
Eat only the fiddleheads. The rest of the fern is poisonous. Eat only cooked fiddleheads, never raw ones, and only from positively identified fern species that you know to be edible.