The largest bat colony in the world (yes, THE WORLD) is not far from here. Local garden stores sell bat guano from it (that cave has been "mined" for bat guano since at least the Civil War). Proceeds from the sale go towards bat conservation.
Opening up the bag it smells JUST LIKE a bat cave. (or any other place bats roost... not uncommon to get a whiff of guano walking around old buildings or parking garages round here)
I buy it because it's for a good cause, in addition to being a great source of nitrogen. There is a disease you can get from inhaling fresh guano if you go crawling in a bat cave (some kind of fungus that gets in your lungs), but this stuff is supposed to be safe. Besides, it's not like I want to go sticking my face in the bag.
