Two years ago, I came upon these two dudes on a highway in the middle of nowhere. They were selling these giant mushrooms which they'd collected in the bush:
The mushrooms grow only on termite mounds and appear a few days after good rain showers and cloudy, misty weather. I've been told, but unable to substantiate as fact, that the spores are distributed through the dung of cattle, whereafter they're transported into the mounds and nurtured by the termites.
It is also said that they only grow on the northern side of the mounds, i.e. away from direct sunlight.
When buying Omahova it is best to get them before they open-up like the ones in the pics. When they're open they go soggy very quickly and are prone to worm infestations.
The last pic is to illustrate how big the termite mounds can be, though some of them get a lot bigger.
I'm not usually very fond of mushrooms, but I'd kill for these. When prepared by someone who knows how to, they're divine. One method is to cut the stems as steaks and poach in buttered, fried onions, ... mmmm