Darkfield and polarised light micrograph of a fruit fly (Drosophila melanogaster) larva. Fruit fly larvae hatch from eggs laid by adult female fruit flies, and undergo a series of moults as they grow and develop into mature adults. The first instar larvae are small and worm-like, and have a simple digestive system with a single tubular intestine. As the larvae grow and moult into subsequent instars, they develop additional segments and specialised organs, including mouth hooks and spiracles for breathing. Fruit fly larvae feed voraciously on decaying fruit and other organic material. They are also an important model organism for studying the genetics of development, as they develop rapidly and are easy to culture in the laboratory. One of the most important discoveries made through studying the larval stage of the fruit fly is the concept of the homeobox genes and the Hox gene complex. These genes are involved in controlling the development of body segments and appendages, and have been found to be highly conserved across a wide range of animal species, including humans.