In the animal category, the bear wins in terms of the land animal with the best sense of smell—mainly because its brain is a third of the size of ours, yet the part devoted to smell is five times larger. Bears also have large noses with special interior folds that carry thousands of smell receptors. The giant male silk moths (Bombyx mori) are thought to have the best sense of smell in the insect world. Their antennae are covered with about 65,000 tiny bristles, most of which are chemoreceptors. And the winner in the fish category is the shark—a fish that has two-thirds of its brain dedicated to smell—allowing it to detect a drop of blood from more than a mile away.
In the insect world, the giant male silk moth is believed to have the most acute sense of smell.