Figure 2. Three headwidths plotted against body length of Solenopsis invicta. Headwidth becomes increasingly allometric from the clypeal region to the vertex. The slopes of the regressions are 1.05 (isometric) below the eyes (HW3), 1.14 across the eyes (HW1) and 1.24 above the eyes (HW2). Head shape thus changes as body (and head) size increase, as can be seen in the scale drawings of a small worker head (left) and a large one (right).