The nervous system of insects is complex, including a number of ganglia and a ventral, double nerve cord. Yet ganglia also use sensory output. A grasshopper with one wing removed can correct for this loss and maintain flight, using sensory input from its brain. Sense organs are complex and acute. In addition to ocelli and compound eyes, some insects are quite sensitive to sounds, and their chemoreceptive abilities are astounding.
Insects are dioecious and fertilization is internal in most.
The manner in which growth is accomplished is an especially important characteristic of insects. In some, hatching eggs produce miniature adults, which to grow must shed their exoskeleton in a process called ecdyisis. These larval forms usually live in different habitats, eat different foods, and assume a body form completely different from that of their parents. The larva feeds and grows, molting its skin periodically. At some point larval growth is completed, the larva stops feeding and builds a case or cocoon around itself.