The Hessian fly (Mayetiola destructor) lays its eggs in the grooves on the upper side of a wheat plant leaf (A). Larvae move toward the base of the plant and feed on the stem (B). The pupal stage (C) is often called the “flax seed stage,” due to the puparium’s resemblance to a flax seed. (Image originally published in Schmid et al 2018, Journal of Integrated Pest Management)