Shark’s-fin soup may be a stereotypical indulgent food for some middle-class Thais, but many of the people where I live have never even heard of it.
Het khon (เห็ดโคน), Termitomyces fuliginosus, a cone-shaped termite mushroom, is the most coveted food in our region of rural Central Thailand. When it sprouts many villagers abandon their normal work and, getting up early, head for the hills to gather this mushroom. Those adept at guessing where the mushroom grows can make a week’s wages in a single day this way. The price paid here is $10 per kilogram, but $20 or more may be paid in Bangkok. Most of the villagers don’t sell the mushrooms, however. The prefer to consume this delicious nutritious food themselves. (There are many ways to serve it: with vegetables, in a curry, pickled, etc. A large restaurant on the Asia Highway, halfway between Bangkok and Chiang Mai, specializes in this mushroom.)
The mushroom sprouts only on a few days per year, however, and must be picked within a day or two. Villagers watch the weather carefully, and know from experience when the mushroom can be found.
AFAIK, the mushroom cannot be cultivated. Or, rather, it is never cultivated by people – it exists only when it is cultivated, but it is cultivated by termites. (If you Google “macrotermitinae termitomyces” you’ll find references to the world’s largest mushrooms, but that isn’t the same species as we eat here.)