We investigated the effects of insect herbivory on the common milkweed (Asclepias incarnata), 78 root stocks were potted in 4L pots in a greenhouse. At the height of 61 to 76 cm, the plants were divided into three different treatment groups of the control (well watered), moderate drought, and severe drought groups with26 individuals per treatment. Two weeks after the treatments were implemented, 13 plants from each group were defoliated by monarch caterpillars (Danaus plexippus). Photosynthesis, height, leaf area, caterpillar weight and time of flowering will be measured. We hypothesized the drought stressed groups would be better able to tolerate defoliation due to the increased allocation of energy towards defense, while the control group allocated more for reproduction.