Dobsonfly
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| Male Eastern Dobsonfly (Corydalus cornutus) Male Eastern Dobsonfly (Corydalus cornutus)
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Chloronia |
Dobsonfly is the common name for any of the soft-bodied, holometabolous insects comprising the subfamily Corydalinae of the megalopteran family Corydalidae, characterized by four large, many-veined wings, with many adults noteworthy for their large size and males of some species conspicuous for extremely elongated mandibles. The Eastern dobsonfly (Corydalus cornutus) can reach 12.5 centimeters (five inches) in length and wingpread, and the males have mandibles of 2.5 centimeters (1 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 with bizarre looking postocular flanges (Contreras-Ramos 1997b). As such dobsonflies add to the wonder of nature for humans, while the adults and larva 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 biologist 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). Adults of this order exhibit an enlarged and fan-folded anal area of their hind wings, and 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, 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, contains two extant subfamilies, Corydalinae (dobsonflies) and Chauliodine (fishflies). Adults of Corydalinae are distinguished by a subquadrate head with postocular ridge, postocular plane, and postocular spine; a microsetose gular setation (region); and a well developed ninth gonostyll (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 1 inch (25 mm)—that they typically are unable to harm humans, as 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, dobsonfly larvae differ markedly from the adults. Insects that undergo holometabolism pass through a larval stage, then enter a non-feeding, outwardly inactive state as a pupa, and finally emerge as adults (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 was 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, deposit their eggs near the water (often on overhanging vegetation), then die. They are primarily nocturnal, and like most aquatic insects, are commonly attracted to bright lights.
Taxonomy
The Megaloptera order were formerly considered part of a group then called Neuroptera, together with lacewings and snakeflies, but these are now generally considered to be separate orders, with Neuroptera referring to the lacewings and relatives (which were formerly called Planipennia). The former Neuroptera—particularly the lacewing group—are nonetheless very closely related to each other, and the new name for this group is Neuropterida. This is either placed at superorder rank, with the Endopterygota, of which they are part, becoming an unranked clade above it, or the Endopterygota are maintained as a superorder, with an unranked Neuropterida being a part of them.
The Megaloptera include two families, Sialidae (alderflies) and Corydalidae (dobsonflies and fishflies), and in turn, the Corydalidae contains 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 (1 species)
- Protohermes. Northwest India to Indonesia, Japan, and China (ca. 42 species)
- Neurhermes. Northwest India to Indonesia and China (8 species)
- Acanthacorydalis. Northeastern India to China and Vietnam (ca. 7 species)
- Neuromus. Northwest India to Indonesia and China (4 species)
- Neoneuromus. Northwesst India to China and West Malaysia (ca. 8 species)
- Platyneuromus. Mexico to Panama (3 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). Retrieved May 24, 2008.
- Contreras-Ramos, A. 1997b. Corydalinae. Dobsonflies, hellgrammites. Tree of Life web project, version 15 (November 1997). Retrieved May 24, 2008.
- 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.
External links
- AgriLife extension, Texas A&M: Dobsonfly. Retrieved May 24, 2008.
- Tree of Life: Corydalus. Retrieved May 24, 2008.
- Dobson Fly page at "What's That Bug". Retrieved May 24, 2008.
- Hellgrammite page at "What's That Bug". Retrieved May 24, 2008.
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