Dobsonfly
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Chloronia |
Dobsonfly is the common name for any of the insects comprising the subfamily Corydalinae of the megalopteran family Corydalidae, characterized by complete metamorphosis, four large wings having many veins, soft bodies, and many of the adults being noteworthy for their large size with males of some species having extremely elongated mandibles. The Eastern dobsonfly (Corydalus cornutus) can reach 12.5 centimeters (five inches) in length and wingspread, and the males can have mandibles of 2.5 centimeters (one inch) or more. The predatory larvae of dobsonflies have strong, biting mouthparts and are known as hellgrammites.
The dobsonflies include some of the largest and most impressive of living insects, with some having disproportionately long mandibles and others having a bizarre-looking, flattened protuberance behind each eye. As such dobsonflies add to the wonder of nature for humans, while the adults and larvae also play key roles in aquatic and terrestrial food chains. Hellgrammites, which are an important component of the benthic macroinvertebrate fauna of rivers and streams, are well-known to fisherman and aquatic biologists given their large size, endurance as bait, and rather ferocious nature (Contreras-Ramos 1997a).
Overview and description
Dobsonflies belong to the Megaloptera order of insects. This order includes two families, Sialidae (alderflies) and Corydalidae (dobsonflies and fishflies). The order is entire aquatic in the sense that all (or nearly all) megalopteran species undergo at least one aquatic stage (Contreras-Ramos 1997a). The hind wings of adults of this order include a section closest to the anus that is enlarged and folds like a Japanese fan. The larvae are elongate, with well-developed chewing mouthparts (Contreras-Ramos 1997a). Members of the more nocturnal Corydalidae tend to be large (forewing longer than 15 millimeters and wingspan up to 180 millimeters), pale yellow to brown to spotted black, and have ocelli (simple light-sensing eyes), while members of the more diurnal Sialidae tend to be small (forewing 15 millimeters or less), dark brown to gray and black, and lack ocelli (Contreras-Ramos 1997a). Megaloptera undergo the most rudimentary form of complete metamorphosis among the insects. There are fewer differences between the larval and adult forms of Megaloptera than in any other order of holometabolous insects.
The family to which the dobsonflies belong, Corydalidae, comprises two extant subfamilies, Corydalinae (dobsonflies) and Chauliodine (fishflies). Adults of Corydalinae are distinguished by an approximately square head with the regions of postocular (behind the eye) ridge, plane, and spine; a region of the upper throat covered with microsetose setation (many short bristles); and well-developed ninth gonostyli (which are appendages of the genital segment) (Contreras-Ramos 1997b). Their wingspans measure between 45 millimeters and 180 millimeters (Contreras-Ramos 1997b). The dobsonfly larvae can be distinguished on the basis of the lateral abdominal filaments on segments 1-8, with the last abdominal segment with a pair of filaments and separated into two, clawed prolegs, and ventral gill tufts on abdominal segments 1-7 (Contreras-Ramos 1997b).
Both male and female dobsonflies can reach substantial lengths, up to 12.5 centimeters (five inches) measured from the tips of their pincers to the tips of their four wings, which, when not in use, are folded along the length of their walkingstick-like bodies. Their wingspans can be twice as long as their body length, and the wings themselves are densely lined with intersecting veins. Additionally, dobsonflies have segmented antennae similar to ants and wasps.
Though both male and female dobsonflies have sharp mandibles, those of an adult male dobsonfly are actually so big—up to one inch (25 mm)—that they typically are unable to harm humans, as they have such poor leverage that they are incapable of breaking the skin. They are used exclusively during mating, where males show them off and grasp the females during copulation. Female dobsonflies, however, retain the short, powerful pincers they had as larvae, so they can inflict painful bites, which can draw blood. Nonwithstanding the males' inability to inflict harm, when threatened, both sexes will raise their heads and spread their jaws menacingly. They are not poisonous, but possess an irritating, foul-smelling anal spray as a last-ditch defense.
Dobsonflies have been found in North America, Central America, South America, Africa, Asia, and Australia. It has been estimated that there are about 100 named species of Corydalinae (New and Theischinger 1993), with about half found in the New World. These species typically are placed into nine genera (Contreras-Ramos 1997b). The most well-known of the numerous species is Corydalus cornutus, the eastern dobsonfly. This is a long, dark-colored insect found in North and Central America.
Life cycle
As insects that undergo complete metamorphosis, also called holometabolism, dobsonflies exhibit a larval form that is markedly different from the adult form. Insects that undergo holometabolism pass through a larval stage, then enter a non-feeding, outwardly inactive state as a pupa, and finally emerge as an adult (the dobsonfly imago).
Dobsonflies spend most of their life in the larval stage. Dobsonfly larvae are called hellgrammites, and are familiar to anglers who like to use the chunky larvae as bait. Hellgrammites live under rocks at the bottoms of lakes, streams, and rivers, and prey on other insect larvae.
After a few years of living and growing underwater, the larvae crawl out onto land and pupate under a rock or log near their aquatic habitat. They spend several days as prepupae, then molt and become larvae that are exarate (with free appendages, not stuck to the body) and decticous (with fully articulated mandibles that are used for emergence from the pupal enclosure), and are capable of defensive bite (Contreras-Ramos 1997a). Members of Corydalidae tend to stay in the enclosure for 8 to 24 days before emerging as adults (Contreras-Ramos 1997a).
Upon emerging, adults live for only a week or so, and do not feed, although they may drink water or sweet solutions (Contreras-Ramos 1997a). Corydalus cornutus adults have been recorded to live an average of eight days (Contreras-Ramos 1997a). While not generally believed to eat during their adult stage, some captive female specimens have been observed with their heads burrowed into blackberries.
Adults can generally be found from late spring into the middle of summer, preferring to remain near bodies of water, particularly the ones where they grew up. Once they emerge as adults they mate, females deposit their eggs near the water (often on overhanging vegetation), and both males and females soon die. They are primarily nocturnal, and like most aquatic insects, are commonly attracted to bright lights.
Taxonomy
The Megaloptera order was formerly considered part of a group called Neuroptera that also included lacewings and snakeflies, but these latter two are now generally considered to be separate orders and Neuroptera is considered to comprise only the lacewings and relatives that were formerly called Planipennia. The former members of Neuroptera are nonetheless very closely related to each other and together they comprise the newly-named group Neuropterida. This is either placed at the superorder rank along with the Endopterygota with the two becoming an unranked clade, or Neuropterida is simply included as a part of the superorder Endopterygota.
The Megaloptera include two families, Sialidae (alderflies) and Corydalidae (dobsonflies and fishflies), and in turn, the Corydalidae comprises two extant subfamilies, Corydalinae (dobsonflies) and Chauliodine (fishflies).
The following are the eight genera of dobsonflies commonly recognized, with their distribution and numbers of known species (Contreras-Ramos 1997a):
- Megaloptera
- Sialidae (alderflies)
- Corydalidae
- Chauliodine (fishflies)
- Corydalinae (dobsonflies)
- Chloroniella. South Africa (one species)
- Protohermes. Northwest India to Indonesia, Japan, and China (ca. 42 species)
- Neurhermes. Northwest India to Indonesia and China (eight species)
- Acanthacorydalis. Northeastern India to China and Vietnam (ca. seven species)
- Neuromus. Northwest India to Indonesia and China (four species)
- Neoneuromus. Northwest India to China and West Malaysia (ca. eight species)
- Platyneuromus. Mexico to Panama (three species)
- Chloronia. Southeastern Brazil to Mexico (15 species)
- Corydalus. Southeastern Brazil and northern Argentina to southern Canada (30 species)
The New World dobsonflies are Platyneuromus, Chloronia, and Corydalus, and are considered to comprise a monophyletic group (Contreras-Ramos 1997b).
ReferencesISBN links support NWE through referral fees
- Contreras-Ramos, A. 1997a. Megaloptera. Alderflies, dobsonflies, fishflies Tree of Life web project, version 14 (October 1997).
- Contreras-Ramos, A. 1997b. Corydalinae. Dobsonflies, hellgrammites Tree of Life web project, version 15 (November 1997).
- Integrated Taxonomic Information System (ITIS). 2004. Corydalinae ITIS Taxonomic Serial No.: 666125. Retrieved May 24, 2008.
- New, T. R., and G. Theischinger. 1993. Megaloptera (alderflies, dobsonflies). Handbuch der Zoologie, Volume IV, Part 33. Berlin: Walter de Gruyter. ISBN 3110135663.
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