Why don the monarchs die or get sick when they eat the milkweed during the caterpillar stage?
Monarchs have evolved to be able to tolerate the toxins in the milkweed. However, several studies have shown that milkweed species that have very high levels of toxins are harmful to the monarchs, and that they do best on species with moderate amounts of toxin. Dr. Karen Oberhauser University of Minnesota Department of Ecology 1987 Upper Buford Circle St.
