Question: what do birds and squirrels have in common? Answer: birdseed. Both birds and squirrels love the stuff, and routinely battle for rights to the backyard feeder. But it's not an equal fight; most squirrels are bigger than the average neighborhood bird. So, chances are a local cadre of squirrels is going to hog all the seed.
Unless, that is, you buy your birdseed from a company called Squirrel Free Incorporated. Squirrel Free's founder, Dr. Joseph Dunn, developed the idea for squirrel-safe birdseed while doing research on cancer. Among the many chemicals under study was capsaicin, the substance that creates a "hot" sensation when you eat a chili pepper.
Studies showed that mammals, including squirrels, have receptors on the tongue and in the mouth that react to chili peppers by sending heat and pain signals to the brain. Although there's no lasting damage, the sensation makes it seem as though the mouth is on fire.
Birds lack the receptors that make chewing chili peppers such an eye-watering experience--they can eat peppers all day and never feel a thing. This is good for the plant--the birds spread its seeds far and wide. Putting two and two together, Dunn laced birdseed with chili pepper to create a seed that squirrels can't swallow. He even received patents for his invention called "Treated Bird Seed Preferentially Palatable to Birds but Unpalatable to Animals having Capsaicin Sensitive Receptors." Catchy, no?
No matter what it's called, squirrels around the world are learning one thing fast: chili pepper seed is strictly for the birds.