Forests are rich grounds for hunters. Some of the greatest riches from hunting, however, lie underground, if you know where and how to look.

Truffle hunting is a hidden world in more ways than one. Across Europe there is no great secret to the types of forests where these edible fungi might occur naturally. But this is only the beginning of the search. The most successful truffle hunters have an intimate understanding of soils, trees and the landscapes which favour truffle growth. They also have a well-trained dog.

I recently went on a truffle hunt in north east Italy with Enrico and Ape (pronounced ‘appy’), his truffle dog. We left early in the morning. Ape sensed she was going on a hunting trip as Enrico walked across the garden to release her from the wire compound. She bounded towards the car and the open boot. One leap and she was in her cage, ready to sniff out truffles.

Ape is a Brittany spaniel, a breed normally associated with bird hunting. She has been trained by Enrico to sniff out the odours associated with the best truffle species. Enrico keeps a close eye on where she goes, and, after a successful discovery, gives her a reward of biscuits. Sometimes her hunting instincts kick in and she’s sharply reminded by Enrico to ignore distracting smells and concentrate on truffles.

Enrico drives past the first potential truffle site, a nearby village to where he lives. “There is a truffle hunter who lives here and the rule is that we do not invade other people’s collecting areas.� Truffle collectors carefully guard their hard-won knowledge of good places to hunt. Some areas are well known. It is difficult to conceal a parked car on narrow country roads. Enrico tells me that some of the older collectors are opening up about their favourite sites, aware that priceless local knowledge might be lost.

Truffle dogs are valuable, reflecting the riches the hunter might reap. You can buy dogs already trained, with one website quoting $12,500 in the USA (where truffles are also hunted), but in north east Italy €1000 is a more reasonable price. As with so much of the truffle business, it is not clear how many dogs are traded. I suspect most people train their own.

As to the fabled riches that lie underground, 2015 has been a hugely disappointing year. Prolonged drought early in the year stymied the growth of primordia, the young fungus-roots on which the truffles will eventually mature a few months later. I was surprised to learn that in this region several truffle species are produced throughout the year, though the highest quality white truffles, the most valuable of all, occur later in the year.

Prices vary hugely, depending on season, species and who you sell to. In north east Italy, white truffles might cost €1000 – 2800 per kg for the final consumer, more for the exceptional, outsize specimens that catch the newspaper headlines. Black truffles are the next most valuable species, around €600 per kg, also retail. Hunters receive about half the retail price. Enrico stresses these are only guideline figures, masked by the informal trade in truffles and the dominance of a few major buyers. I ask Enrico to estimate the total value of the truffle market across Italy in a year. “Around €50 million,� he reckons, “the amount the hunters receive. The added value is much higher, about €200 million.�

Truffle collectors have to sit an exam each year, with 60 multiple choice questions aimed at testing their knowledge of how to collect (no rakes) and so safeguard future harvests. Collectors must know about land rights and respect other forest users. Enrico always carries his license, though he’s never had to show it to the forest rangers. There are over 70 000 official truffle collectors in Italy. The exam and license system might suggest a close regulation of the truffle trade, but much remains unknown about how it operates.

The truffle business in Italy is self-organizing and self-sustaining, and by all accounts it works well. Yet a lack of transparency creates doubts about the fairness of transactions and weak data undermines confidence in the the sustainability of collecting from the wild. Enrico was contacted several times during my short stay by fellow truffle hunters. Mobile phones help to share useful information and swap experiences for mutual benefit. But networks of hunters tend to be local while buyers operate on a larger scale, and some information is too valuable to an individual hunter to share with others.

Researchers need to respect local knowledge and handle their natural curiosity with care. Not all information needs to be shared, and knowledge may at times be most valuable when it is kept in the minds of those who possess it.

There are few obvious weaknesses in the current system of light regulation and the strong code of conduct amongst professional hunters. Making local knowledge public would undermine the existing trade. Yet there are other ways in which research can support the truffle business. Greater openness on trade, for example, would provide clearer evidence of sustainable yields, and give the truffle hunters a stronger position in getting the best prices for their underground riches.