A couple weeks ago, Enterprise Farm sent us a bag of fiddleheads (which we've enjoyed before). Anna popped one in her mouth while putting the rest of the vegetables away, and then found the note in the bottom of the box:
***Fiddleheads should always be cooked thoroughly before eating.*** Fiddleheads contain a somewhat mysterious toxin that when eaten raw can cause symptoms similar to food poisoning. After a good washing, the greens should always be cooked in boiling water for 15 minutes or steamed for 10 to 12 minutes until tender.She spat out the partially masticated vegetable, and then helpfully highlighted "toxin," "food poisoning," and "should always be cooked" in the note, which Jack and I found when we decided to eat the fiddleheads a few days later.
We were torn. Fifteen minutes of boiling is not the kind of treatment we would subject any nice tender green vegetable (asparagus, green beans, Brussels sprouts) to, much less our once-a-year fiddlehead treat.
On the other hand. Killing your housemates. Also not our favorite.
To the Internet!
It seems that most of the concerns about eating raw (or lightly cooked) ostrich fern fiddleheads stem from a couple sets of food poisoning cases in 1994. (Oh, actually, here's a more recent case from Alaska.) Because the cause of the food poisoning-like symptoms were not determined, but it is suspected to be a toxin in the ferns that is destroyed or inactivated by heat, we now have these long-cooking requirements. (There may also be some confusion with another type of fern, bracken fern, which does contain carcinogens.)
We split the difference, and steamed our fiddleheads for 6 minutes. Then we mixed them with some homemade hollandaise and fettucine, yum. So, while I can't actually recommend that you not follow well-meaning and Canadian-government-endorsed guidelines, I can add the anecdata that we are still alive and kicking.
(I later asked some fledgling farmers/urban homesteaders for advice, and they also suggested cooking times in the five-minute range.)