Which is the first rodenticide developed?

Red squill is the first rodenticide developed.
Red squill, a rodenticide derived from the bulbs of a lilylike subtropical plant, is slower-acting and less toxic to animals other than rodents because it is removed from the stomach by vomiting a reflex that is absent in rodents.
The powdered bulbs of a Mediterranean plant, red squill, have been widely used as a rat poison, since the toxic action of red squill is relatively specific to rats.