While out on our winter walks we will often come across plants with galls. You may see these growths on the stems and tips of plants. They are often in the shape of round balls or irregular masses. These are galls, they are tumor-like growths that are formed by the feeding of insect larvae. They are produced by a chemical reaction between the insect that lays the eggs, and the chemicals of the plant itself. This causes the growing tissues of the plant to swell around the eggs. The cell growth is accelerated by secretions from the larvae. The gall provides food, shelter from extreme weather, and protection from predators, mainly birds, squirrels, and mice. There are more than 1500 species of insects that produce galls. Most of the insects are wasps, aphids, midges, and flies. Each insect species has a specific plant that it will lay its eggs on and thus form a gall. Some galls are harmful to the plant while others can be so numerous as to distort and sometimes cover the plant almost entirely. One gall, the willow pine cone gall, is found growing at the tips of willow shrubs. A small gnat (Rhabdophaga strobiloides) lays its eggs at the growing tip of the branch. The gall is shaped by many overlapping and tightly formed leaves, resembling a pine cone. It is host to a whole community of living organisms, interacting as a food web, overwintering, feeding, and breeding. In one study 23 galls were collected. 564 insects were reared from them. 6 wasp parasites, 384 meadow grasshopper eggs, and 169 other guest gnats were also found. Quite an impressive number in only 23 galls. Only 15 galls had the original larva of the gnat. Two other commonly found galls are the Goldenrod Ball Gall or Elliptical Gall. We come across these quite frequently. The first is caused by a tiny fly and the second by the larva of a particular moth. Next time you see galls when you are out and about, try to imagine the number of insects that my be residing inside them. Everyone needs a home in winter!