The female silk worm moth (Bombyx mori) makes the pheromone bombykol in a special organ in her abdomen. When she is prepared to mate she releases this to attract males. A male silk worm moth has two long antennas that are very sensitive to the odor of the female. One single molecule is enough to cause a reaction in the sensory cells on the male's antenna. In this way he can locate the female. Even at a distance of 10 kilometers, he can still smell her!