 It is thought the beetle, which as an adult feeds on the foliage of the plant, and its early instars, which eat the roots,  derive a measure of protection from predators by incorporating toxins from the plant into their bodies, thereby becoming distasteful, much as the monarch butterfly and its larvae do.They feed by opening veins in the milkweed plant, decreasing the beetles' exposure to latex-like sap.When startled, the beetles make a shrill noise.