Aphids, also called plant lice or aphis, are small (up to ¼ inch), soft-bodied insects that infest most garden plants. Some aphids spend their entire life on one type of plant; others infest several different plant species. Aphids have a complicated life history because they produce an additional form besides male and female aphids. Aphids that hatch from overwintering eggs are wingless females, called stem mothers. They give live birth without fertilization by a male. Many generations of only females may be produced throughout the summer. Some of these aphids develop wings so they can fly to less densely populated plants, or to another species of plant. In the fall, female aphids give birth to males and females that mate and produce the fertilized eggs that survive the winter. In warm climates there may be continuous production of living young, with no development of sexual males and females. Large numbers of aphids may cause little damage to a plant; or just a few aphids on a plant may cause severe distortion and stunting. Certain aphids are also vectors of plant diseases (see Vectors of Plant Diseases).