A simplified life cycle of hemlock woolly adelgid. (Adelges tsugae). The species follows an unusual life cycle in eastern North America, in which it reproduces through parthenogenesis—i.e., reproduction without fertilization, in which females produce offspring that are (roughly) clones of herself—and proceeds through two generations in a year’s time. The spring generation produces some winged females that cannot produce, while the rest remain wingless adults that do lay eggs (as is the case for all of the winter generation). A single tree with a heavy infestation can have millions of adelgids on it. (Image credit: N.P. Havill and V. D’Amico, published in Limbu et al 2018, Journal of Integrated Pest Management)