Where Did Rat Poison Come From?

Rats and certain other vermin are difficult to kill with poisons because their feeding habits reflect their place as scavengers. They will eat a small bit of something and wait, and if they don't get sick, they continue. A good rat poison must be tasteless and odorless in lethal concentrations, and have a delayed effect.
There are several types of rodenticides available. The traditional products are called anticoagulant rodenticides and are discussed here. If one intends to use a rodenticide we encourage you to choose this type over others as there is a readily available antidote for the anti-coagulant rodenticides. Other rodenticides are more toxic and no antidote is available.
In 1921, ranchers were dismayed at the sudden onset of lossage in their herds due to a strange condition: the animals bled to death. Small cuts failed to heal. The roughage cows eat will scratch their digestive systems, but unlike the normal case where such scratches are minor and readily heal, these scratches failed to heal and the animals died from internal hemorrhaging. What seemed odd was that the animals were being fed hay from fields that appeared not dissimilar from that of previous years. No sudden invasive plants of a poisonous nature had been found.
A researcher by the name of Karl Paul Link, working under the aegis of the Wisconsin Alumni Research Fund (WARF), did a careful analysis of the ensilage from ranches that suffered losses and those that did not. He discovered that a chemical, dicoumorin, found in the ensilage of sweetclover hay from those ranches suffering the losses, was a powerful anticoagulant. Dicoumarin is the result of a substance called coumarin, which is the chemical which gives new-mown hay its characteristic smell, being subjected to the heat and mold in a silo, and forming a double molecule. The year of the serious losses had been an unusually warm one after the ensilage was created.
And it is with this checmical that the modern day Rat Poisons are derieved from. They are lethal enough to kill off an entire colony of rats!
Single feed baits are chemicals sufficiently dangerous that the first dose is sufficient to kill.