The dobsonfly, a member of the order Megaloptera and the family Corydalidae, is one of the most physically imposing insects found in North America and Asia. Determining how large a dobsonfly gets requires separating the measurement of the main body from the total length, which can be significantly altered by the male’s specialized head structure. The answer is also complicated by the comparison between the short-lived flying adult and its much longer-lived aquatic larval stage.
Adult Size and Dimensions
The body of a typical adult dobsonfly, measured from the head to the tip of the abdomen, usually falls within a range of 2 to 3.5 inches (5 to 9 cm). This measurement excludes the male’s unique mandibles, providing a clear baseline for the insect’s torso size. The large, membranous wings of the dobsonfly can stretch between 4.5 and 7 inches (12 to 18 cm) across when fully extended. This wide wingspan classifies them among the largest non-moth insects in temperate zones. In rare cases, the body of the largest Asian species, Acanthacorydalis fruhstorferi, can reach up to 4.1 inches (10.5 cm), with a wingspan recorded at 8.5 inches (21.6 cm). These dimensions highlight why the order name Megaloptera translates to “large wing,” making the adults conspicuous when they emerge near water sources.
The Role of Sexual Dimorphism
The question of size becomes more complex due to sexual dimorphism, the physical difference between males and females of the same species. Adult male dobsonflies are easily identified by their dramatically elongated, tusk-like mandibles, which are used primarily in mating rituals and competition for females. These mandibles can add a significant length to the overall profile of the insect, sometimes measuring up to 1.6 inches (40 mm) long in the Eastern Dobsonfly (Corydalus cornutus). While the male’s body may be slightly smaller than the female’s, these exaggerated jaws can increase the male’s total length to nearly 5 inches. Despite their intimidating appearance, the male’s long mandibles are too unwieldy to deliver a meaningful bite to a human. Conversely, the female possesses shorter, more robust mandibles capable of inflicting a painful, defensive pinch.
Size of the Larval Stage (Hellgrammites)
Before the large, winged adult emerges, the insect spends several years in its aquatic larval stage, commonly known as the hellgrammite. Hellgrammites are robust, dark-colored predators that inhabit clean, oxygen-rich streams and rivers. These larvae are known for their substantial length, often reaching 3 to 4 inches (75 to 90 mm) before pupating. Hellgrammites possess a segmented body and a pair of strong, biting jaws used for capturing small aquatic prey. They are widely recognized by anglers, who consider them a prime natural bait for fish. The hellgrammite’s length is comparable to or even exceeds the body length of the adult, making the larva a significant presence in the aquatic environment.