Flies, which belong to the scientific order Diptera, undergo a developmental pathway known as holometabolism. This process involves four distinct life stages, where the early stages look drastically different from the final winged form. Understanding the terminology for these early stages clarifies the biology of this common creature.
The Specific Names for Fly Offspring
The general biological term for the immature stage of an insect undergoing complete metamorphosis is the larva. For a true fly, the soft-bodied, legless larva is most accurately referred to as a maggot. This name applies to the larvae of many fly species, including the common house fly and blow flies.
The term “grub” is sometimes used broadly for insect larvae, but it usually describes the thick, cylindrical larvae of beetles. A maggot is distinct from a grub because it lacks a well-defined head capsule and true legs, typically having a tapered body shape.
The Four Stages of Metamorphosis
Flies develop through a four-stage life cycle called complete metamorphosis. The cycle begins when the female adult fly deposits tiny eggs, often in clusters, on a suitable food source like decaying organic matter. This placement ensures the offspring have immediate access to nourishment upon hatching.
The second stage is the larva, or maggot, which emerges rapidly from the egg, sometimes within 24 hours under warm conditions. The maggot’s purpose is to consume food and grow, shedding its skin multiple times in phases known as instars. Once the larva reaches its full size, it transitions into the third stage, the pupa.
During the pupal stage, the maggot seeks a dry spot and forms a hardened, protective outer shell called the puparium. Inside this casing, the larval tissues are reorganized into the structures of the adult fly. Finally, the adult fly emerges from the puparium, ready to reproduce.
Life and Behavior of the Larval Stage
The fly larva is designed for rapid consumption and growth. Its body is vermiform, or worm-like, lacking the jointed appendages found on other insect larvae. Instead of true legs, the maggot uses its segmented body and internal fluid pressure to move in a crawling motion.
The head end of the maggot is pointed, featuring hook-like mouthparts used to ingest the moist, decaying material it lives in. Maggots are efficient at breaking down organic matter, contributing to their rapid growth from a few millimeters to up to 20 millimeters in just a few days. To breathe while buried, most maggots use a pair of openings called posterior spiracles, located at the blunt end of their body. This allows the maggot to keep its breathing apparatus near the surface while its mouthparts remain submerged and actively feeding.