Pemphigus spyrothecae
 Pemphigus spyrothecae or the poplar spiral gall aphid is a social insect which exhibits apparent altruistic behaviors. The aphids form galls and act as colony defenders at times sacrificing their own lives to do so. It has been shown that colony defense is more likely in habitats that are difficult to obtain and can hold a large number of individuals. These gall locations are so crucial because plants have a short window in which a gall can be produced.