Ampulex compressa larvae develop through three instars. The number of instars of A. compressa were determined by taking representative larva from different time intervals and plotting the product of the length and width of the head capsule (area) against age of the larva. The data plots as three distinct groups, indicative of three instars (green - first instar, orange - second instar, blue - third instar. Horizontal bars represent average area of the head capsule in each instar and vertical error bars are standard deviation. Each mean head capsule size is significantly different from the others, as indicated by the Kruskal-Wallis test (p < 0.0001).