Fiddleheads are ferns and they tend to grow around march-lands or along river banks. New Brunswick, Canada has an abundance of them during the month of May and into June.  Its lobster season in some parts of New Brunswick and fiddleheads love lobster!  Its the perfect example of where the terroir meets the merroir!  New Brunswick has many gastronomic experiences like this.
The locals pick them like crazy to pickle or freeze to savour over time.  But they are best eaten fresh, cleaned, steamed, and with a little butter and vinegar.  The taste lands somewhere between asparagus and broccoli.  But the other plus is, Fiddleheads make a great Cocktail garnish too!  
FYI: my logo is the image of a Fiddlehead :)