BIG AND SCARY
The formidable insect pictured in the last word in the July 18 issue of NewScientist is a male dobsonfly from the genus Corydalus (Order Megaloptera, Family Corydalidae). There are 5 species in this genus residing in Costa Rica: C. clauseni, C. flavicornis, C. luteus, C. magnus, and C. peruvianus. From the picture provided and the indicated size, the specimen is likely Corydalus luteus.
Both male and female dobsonflies can reach lengths up to five inches (12.5 cm). Although the mandibles of males appear intimidating, they are actually harmless to humans. Their mandibles are used exclusively during mating, where males show them off and grasp the females during copulation. Female dobsonflies, however, have short powerful pincers and can inflict painful bites, which can draw blood.
Dobsonflies spend most of their life in the larval stage, during which they are called hellgrammites, and are familiar to anglers who like to use the large larvae as bait. Hellgrammites live under rocks at the bottoms of lakes, streams and rivers, and prey on other insect larvae with the short sharp pincers on their heads, with which they can also inflict painful bites on humans. Hellgrammites can reach to 2" to 3" in length, with gills along the sides of their segmented bodies that allow them to breathe underwater. After a few years of living and growing underwater, the larvae crawl out onto land and pupate. They stay in their cocoons over the winter and emerge only to mate. Upon emerging, they live for only seven days.
Adults can generally be found from late spring into the middle of summer, preferring to remain near the aquatic areas where they grew up. Once they emerge as adults they mate, deposit their eggs on overhanging vegetation near the water and die. They are primarily nocturnal, and like most aquatic insects, are commonly attracted to bright lights. I collected my first specimen at the light of a gas station restroom in Potomac, Maryland.
