Gracie’s Private Reserve Diatomaceous earth (DE) is the remains of microscopic one-celled plants (phytoplankton) called diatoms that lived in the oceans and lakes that once covered the western part of the US and other parts of the world. These deposits are mined from underwater beds or from ancient dried lake bottoms thousands of years old. DE is used in myriad ways for the control and elimination of pests. It can be used as a food supplement to eliminate worms and parasites. It contains trace minerals including: calcium, magnesium, sodium, potassium, copper, zinc, iron, phosphorous, and selenium. It can also be used externally to rid your pets and home of insects including fleas!