Holometabolism, also called complete metamorphosis, is a form of insect development which includes four life stages: egg, larva, pupa, and imago (or adult). Holometabolism is a synapomorphic trait of all insects in the superorder Endopterygota. Immature stages of holometabolous insects are very different from the mature stage. In some species the holometabolous life cycle prevents larvae from competing with adults because they inhabit different ecological niches. The morphology and behavior of each stage are adapted for different activities. For example, larval traits maximize feeding, growth, and development, while adult traits enable dispersal, mating, and egg laying. Some species of holometabolous insects protect and feed their offspring. Other insect developmental strategies include ametabolism and hemimetabolism. Developmental stages There are four general developmental stages, each with its own morphology and function. Egg The first stage of the insect life cycle is the egg, or embryo, for all developmental strategies. The egg begins as a single cell which divides and develops into the larval form before hatching. Some insects reproduce by parthenogenesis or may be haplodiploid, and produce viable eggs without fertilization. The egg stage in most insects is very short, only a few days. However, insects may hibernate, or undergo diapause in the egg stage to avoid extreme conditions, in which case this stage can last several months. The eggs of some types of insects, such as tsetse flies, or aphids (which are hemimetabolous), hatch before they are laid. Larva The second stage of the holometabolous life cycle is the larva (plural: larvae). Many adult insects lay their eggs directly onto a food source so the larvae may begin eating as soon as they hatch. Larvae never possess wings or wing buds, and have simple rather than compound eyes. In most species, the larval stage is mobile and worm-like in form. Larvae can be classified by their body type: Elateriform: wireworm-like, as in the beetle family Elateridae. Eruciform: caterpillar-like, as in the Lepidoptera and Symphyta. Some that lack legs, such as the larvae of Nematoceran flies such as mosquitoes, are called apodous eruciform. Scarabaeiform: grub-like, with a head-capsule, as in the beetle family Scarabaeidae. Vermiform: maggot-like, as in most species of Brachyceran flies. Campodeiform: similar to members of the genus Campodea, elongated, more or less straight, flattened, and active, with functional legs. The larval stage is variously adapted to gaining and accumulating the materials and energy necessary for growth and metamorphosis. Most