It’s not easy for insects to survive Iowa winters. Some literally can’t - they freeze to death or migrate away to warmer climates. But many insects have adapted to cold temperatures by entering diapause, which is like hibernation. Diapause is a developmental arrest to survive adverse seasons where individuals stop metabolic activity.
Most diapausing insects stop feeding and moving around. They are susceptible to freezing, starving and dehydration during the winter. Diapause is specific to a certain life stage for insects. For example, European corn borer overwinter as 5th instars, bean leaf beetle overwinter as adults, and soybean aphid overwinter as eggs. In preparation for diapause, insects collect energy reserves and move to protected sites (e.g., in the soil, under leaf litter or inside plants). Some species aggregate together, such as multicolored Asian lady beetles. Aggregation in the winter happens for many reasons, but usually masses form as a result of chemical communication within the species.
Insects can employ two survival strategies for cold temperatures: freeze avoidance or freeze tolerance. Freeze-avoidant insects keep their bodily fluids liquid and freeze tolerant insects can handle the formation of internal ice. Insects in Iowa generally avoid freezing because the winter lasts for a long time. Some freeze-avoidant species acclimate for winter by creating cryoprotectants, or antifreeze proteins, in their body (usually 20-30% of fresh body weight!).