Flies belong to the vast insect order known as Diptera, characterized by having only a single pair of functional wings. This order is highly diverse, containing species that range from nearly microscopic to surprisingly large. Identifying the largest fly is not straightforward because “biggest” can be defined by different anatomical measurements. Entomologists must clarify whether they are referring to the longest body, the widest wingspan, or the greatest overall mass.
Defining How Flies Are Measured
Entomologists use specific, standardized metrics to assess the size of flies and resolve debates over record holders. The most common measurement is body length, typically taken from the tip of the head to the end of the abdomen. This metric generally reflects the insect’s overall bulk and weight.
A second common measurement is wingspan, which is the distance from the tip of one wing to the tip of the other when fully extended. Wingspan often determines how imposing a flying insect appears, though a large span does not necessarily mean a heavy body. Mass, or weight, is another factor, but it is often the hardest to measure precisely, especially with live specimens. The largest fly is often considered the one with the greatest combination of length and mass, indicating the most robust build.
The Record Holder for Largest Fly
The species generally recognized as the largest and heaviest true fly is the giant Mydas fly, Gauromydas heros. This impressive insect is a member of the Mydidae family, known for their robust, often wasp-mimicking bodies. The body length of G. heros can reach an extraordinary 70 millimeters (2.8 inches), making it the longest-bodied fly in the order Diptera.
The wingspan of this Neotropical species frequently exceeds 100 millimeters (4 inches), giving it a substantial and powerful appearance in flight. Gauromydas heros is native to parts of South America, including Brazil, Bolivia, and Paraguay, inhabiting areas near leafcutter ant colonies. Its unique life cycle involves the larvae living as predators within the subterranean waste chambers of Atta ant nests, feeding on other immature insects. Adult females are believed to not feed at all, focusing their short adult lives entirely on reproduction, while males sometimes feed on flower nectar.
Other Giant Fly Species
While Gauromydas heros holds the title for overall bulk, other species are noteworthy for specific dimensions. The Japanese crane fly, Holorusia mikado, is often cited as having the largest leg span of any fly species. A specific specimen was measured to have a leg span of 25.8 centimeters (over 10 inches), giving it an enormous reach.
Despite its impressive leg span, the body length of Holorusia mikado is much shorter than the Mydas fly, typically around 48 millimeters, and its wings are comparatively delicate. A different group, the Timber Flies (Pantophthalmidae family), occasionally produces individuals with a body length that rivals the longest Mydas flies. Some specimens can measure up to 78 millimeters long, but they possess a disproportionately smaller wingspan and are heavy-bodied fliers that rarely take to the air.