The immature stages of many aquatic insects are able to remain active throughout the year. Most of these insects are equipped with special body fluids that act as antifreeze and prevent the insects from being harmed by the freezing temperatures. Galls are a common sight on many plants, including weeds, shrubs and trees. The insects and mites are the most common causes of plant galls. Insects responsible for gall formation include gall wasps, gall flies and midges, aphids, caterpillars, beetles and thrips.
Many insects live inside of developing galls.
These galls usually consist of two distinct layers - an outer protective layer and an inner nutritive layer. Through the process of evolutionary trial and error gall insects now feed at the proper rate so that they do not kill all of the developing plant tissue. Thus the gall insect benefits by obtaining reliable food and shelter, while the plant is neither harmed or benefited. There are many types of plant galls and each insect produces a totally unique, characteristically-shaped gall. The variable physical appearance of the many galls is due to the type of insect causing the gall and the part of the plant affected.