Dobsonflies are a

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

s, Corydalinae, part of the

Megaloptera Megaloptera is an order of insects. It contains the alderflies, dobsonflies and fishflies, and there are about 300 known species. The order's name comes from Ancient Greek, from ''mega-'' (μέγα-) "large" + ''pteryx'' (πτέρυξ) "wing ...

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Corydalidae The family Corydalidae contains the megalopterous insects known as dobsonflies and fishflies. Making up about one dozen genera,See references in Haaramo (2008) they occur primarily throughout the Northern Hemisphere, both temperate and tropical, ...

. The

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e (commonly called hellgrammites) are aquatic, living in

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a stream ...

s, and the adults are often found along streams as well. The nine

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

of dobsonflies are distributed in the

Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with th ...

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

, and

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

Etymology

The origin of the word "dobsonfly" is unclear.

John Henry Comstock John Henry Comstock (February 24, 1849 – March 20, 1931) was an eminent researcher in entomology and arachnology and a leading educator. His work provided the basis for classification of butterflies, moths, and scale insects. Early life and ...

used the term in reference to these insects in his 1897 book ''Insect Life'', but did not explain it. He also mentioned that anglers used the word "hellgrammite" for the aquatic larvae they used as bait, but the origin of this term is also unknown.

Description

Adult dobsonflies are some of the largest non-

Lepidopteran Lepidoptera ( ) is an order of insects that includes butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 percent of the total described specie ...

insects of

temperate zones In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

such as the United States and Canada, with a wingspan of up to in some species of ''

Corydalus ''Corydalus'' is a genus of large flying insects in the Corydalidae family, commonly known as dobsonflies. They are endemic to North, Central and South America and there are about 35 known species. Members of the genus have wing lengths of up t ...

''.Stange, Lionel. "Alderflies and Dobsonflies." Encyclopedia of Entomology. 2nd ed. New York: Springer Publishing, 2008. The Asian ''

Acanthacorydalis fruhstorferi ''Acanthacorydalis fruhstorferi'' is a species of dobsonfly native to Vietnam and China. It holds the title of largest aquatic insect by wingspan according to the Guinness Book of World Records at 21.6 cm. The title formerly belonged to the Brazi ...

'' can have a wingspan of up to , making it the largest dobsonfly and the largest aquatic insect in the world by this measurement. The

wings A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expresse ...

vary from a grayish to translucent shade, depending on the species, and the anal region of the hindwing is wide and folded at rest. Despite the large wings, adults are weak, fluttery fliers. The body is soft and coloration varies from yellow to dark shades of brown. The body typically does not surpass in length, although the largest Asian ''Acanthacorydalis'' may reach . Adult males of many—but not all—species are easily recognized by their long, curving

mandibles In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

. Examples of species with large-mandibled males include the genera ''Acanthacorydalis'', ''Corydalus'' and ''Platyneuromus'', while in ''Neoneuromus'', ''Nevromus'', ''Neurhermes'' and ''Protohermes'' the sexes are similar. In ''Corydalus cornutus'', a particularly long-mandibled species, these can reach up to in length and are used in competition for females.Simonsen, T. J., Dombroskie, J. J., and D. D. Lawrie (2008). Behavioral Observations on the Dobsonfly, ''Corydalus cornutus'' (Megaloptera: Corydalidae) with Photographic Evidence of the Use of the Elongate Mandibles in the Male. American Entomologist 64 167-169. It is possible that the mandibles may have been selected as

secondary sex characteristics Secondary sex characteristics are features that appear during puberty in humans, and at sexual maturity in other animals. These characteristics are particularly evident in the sexually dimorphic phenotypic traits that distinguish the sexes of a sp ...

used by females to evaluate males during

courtship Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private m ...

. Males cannot use these mandibles to bite because they are too long; on the other hand, females have short, heavily sclerotized mandibles which enable them to deliver powerful bites when threatened. Males of many species will also produce "nuptial gifts" in the form of packages of nutrient-rich

spermatophores A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...

that are eaten by the female partner after mating. This has been shown to be correlated to mandible size; in species where the males have large mandibles the "nuptial gift" is small or absent, while it is large in species where males lack the exaggerated mandibles. Two genera, ''Chloroniella'' and ''Chloronia'', are unusual in that the males lack large mandibles and do not produce "nuptial gifts". The antennae of males are also noticeably elongated, even longer than the mandibles.

Corydalinae Dobsonflies are a subfamily of insects, Corydalinae, part of the Megalopteran family Corydalidae. The larvae (commonly called hellgrammites) are aquatic, living in streams, and the adults are often found along streams as well. The nine genera o ...

is distinguished from closely related

clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, t ...

by the following

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

(with exceptions in a few species): quadrate head with a postocular spine, ridge, and plane, non-pectinate antennae, four crossveins between the radius and the radial sector, and distinctive male terminalia with a well developed ninth gonostylus. In regards to the larvae,

entomologist Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as arach ...

wrote in his 1897 book Insect Life,Comstock, John Henry (1897). Insect Life. Cornell University Library. Online. "In spite of its disagreeable appearance it is in some respects very interesting to students of Nature study." The larvae, commonly called hellgrammites, are perhaps better known than the adults due to their more readily findable nature. They are unusual in that although they are generally aquatic, taking in dissolved

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

through abdominal lateral filaments and tracheal gills, they also have spiracles that allow them to take in air directly when above water.Contreras-Ramos, Atilano. Corydalus. Tree of Life Web Project. November 15, 1997. Larvae of dobsonflies differ from those of their sister clade, the alderflies, in that they bear eight pairs of lateral processes as well as anal

prolegs A proleg is a small, fleshy, stub structure found on the ventral surface of the abdomen of most larval forms of insects of the order Lepidoptera, though they can also be found on other larval insects such as sawflies and a few other types of ins ...

with a pair of terminal hooks used to hold themselves to substrate, and also in that they lack a terminal filament.Borror, Donald; Triplehorn, Charles; and Norman Johnson. An Introduction to the Study of Insects. 6th ed. New York: Harcourt Brace College Publishers, 1989. 358-363. At the end of the abdomen is a pair of claw-like structures. Body color is black or dark brown.

Systematics

There are about sixty species of dobsonflies. Contreras-Ramos Contreras-Ramos, Atilano (1998). Systematics of the dobsonfly genus ''Corydalus'' Latreille (Megaloptera: Corydalidae). Thomas Say Monographs, Entomological Society of America. Lanham, MD. 360pp. suggests nine

within Corydalinae, divided into four lineages. Working from "most basal" to "most derived" lineages, there are: * The Protohermes lineage, containing the genera '' Neurhermes'' and '' Protohermes'', distributed from Northwest India to Indonesia, China, and Japan. * The Chloroniella lineage, containing the monotypic genus '' Chloroniella'', found only in South Africa. * The Nevromus lineage, containing the genera '' Acanthacorydalis'', '' Nevromus'', and '' Neoneuromus'', distributed from Northwest India to Southeast Asia. * The Corydalus lineage, containing the genera '' Platyneuromus'', '' Chloronia'', and ''

'', distributed from southern Canada down to northern Argentina and south-east Brazil.

Diet and behavior

The larvae of dobsonflies live along the rocky bottoms of streams. Chiefly active during the night, they ambush prey in the middle of

riffles A riffle is a shallow landform in a flowing channel. Colloquially, it is a shallow place in a river where water flows quickly past rocks. However, in geology a riffle has specific characteristics. Topographic, sedimentary and hydraulic indica ...

which supply plenty of oxygen and stir up prey.Hayashi, Fumio (1989). Radio Tracking and Activity Monitoring of the Dobsonfly Larva, ''Protohermes grandis'' (Megaloptera: Corydalidae). Oecologia 78 468-472. They are generalist predators; dissections have revealed that they primarily eat aquatic immatures of

mayflies Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the orde ...

caddisflies The caddisflies, or order Trichoptera, are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the b ...

stoneflies Plecoptera is an order of insects, commonly known as stoneflies. Some 3,500 species are described worldwide, with new species still being discovered. Stoneflies are found worldwide, except Antarctica. Stoneflies are believed to be one of the mo ...

, and

chironomid The Chironomidae (informally known as chironomids, nonbiting midges, or lake flies) comprise a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae. Many species ...

midges.Hayashi, Fumio (1988). Prey selection by the dobsonfly larva, ''Protohermes grandis'' (Megaloptera: Corydalidae). Freshwater Biology 20 19-29. Although the larvae spend most of their lives under rocks below water, locals along Virginia and Pennsylvania rivers have reported emergences, known as "hellgrammite crawlings," during thunderstorms.Hall, Donald. Eastern Dobsonfly. Featured Creatures. University of Florida. April 2013. The adults are also nocturnal, and are seldom seen as they hide under leaves in the

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an a ...

during the daytime. However, they do sometimes form aggregations under bridges or other structures along streams. Since the adults live only about a week, they are not known to eat anything, although they have been reported to drink sweet solution in captivity. The dobsonfly may be attracted by

mercaptan In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...

, an indicator additive in natural gas and propane, and may behave as an

animal sentinel Sentinel species are organisms, often animals, used to detect risks to humans by providing advance warning of a danger. The terms primarily apply in the context of environmental hazards rather than those from other sources. Some animals can act ...

in the presence of these gases.

Life cycle

The

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

from larva to adult in dobsonflies is one of the simplest of the

holometabolous Holometabolism, also called complete metamorphosis, is a form of insect development which includes four life stages: egg, larva, pupa, and imago (or adult). Holometabolism is a synapomorphic trait of all insects in the superorder Endopterygot ...

orders, yet the life cycle begins with an intriguing ritualized

courtship display A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), ...

(most of the following comes from Simonsen et al. 2008 and all pertains to Corydalus; other courtship rituals remain unknown). Males compete with each other for females, aggressively fluttering the wings and trying to place their long mandibles underneath the body of the opponent in order to flip him into the air. Afterwards, the male approaches a female from the side and touches her with his antennae. At first the female reacts somewhat aggressively, moving the head from side to side with mandibles wide apart. However, she then allows the male to come closer and place his mandibles over her wings in a perpendicular position, a position he holds until the female signals reception to mating. At least in '' Protohermes'', during copulation the male attaches to the female's

genitalia A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...

a large, globular

spermatophore A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...

about 4 mm long and wide. The spermatophore consists of two parts: a large gelatinous mass, and a smaller seminal duct containing the sperm. After copulation, the female proceeds to spread her legs wide apart, curl the abdomen under the chest, and eat the gelatinous part of the spermatophore.Hayashi, Fumio (1992). Large spermatophore production and consumption in dobsonflies ''Protohermes''. Japanese Journal of Entomology 60 59-66.

Oviposition The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...

occurs along rocky walls of streams at night, from May to September in ''Corydalus''.Mangan, Brian (1992). Oviposition of the Dobsonfly (''Corydalus cornutus'', Megaloptera) on a Large River. American Midland Naturalist 127 348-354. The females deposit coin-size

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

masses containing on average one thousand grey, cylindrical eggs, each egg about 1.5 mm long and 0.5 mm wide. This mass is covered by a layer of a chalky, white substance, which probably protects the eggs from

desiccation Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. ...

and overheating. Females tend to deposit egg masses at relatively few sites, resulting in grouped egg masses. One to two weeks after oviposition, the eggs hatch and the first

instar An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...

larvae either fall directly into the stream or if not, immediately search for water. There the larvae live for up to five years, going through 10-12 instar molts. When they have finally reached maturity, the larvae leave the water and find a rock, log, or anthropogenic debris, typically close to the stream but sometimes up to 40 m away. There they construct a chamber for pupation and spend several days to several weeks as prepupae before shedding the exoskeleton and spending about a week to two weeks as

pupae A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...

. The pupae are yellow-orange with dark spots on the dorsum of the abdomen, covered in minute setae, and exarate (i.e. the developing appendages and mouthparts are attached only at their proximal ends). Although the males have a small tubercle on the

prothoracic The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites (exoskeletal plates) are the pronotum (dorsal), the prosternum (ventral), and the propleuron (lateral) on ea ...

sternum and a slightly wider head than the females, the mandibles are not as noticeably divergent as in the adults.Mangan, Brian (1994). Pupation Ecology of the Dobsonfly ''Corydalus cornutus'' (Corydalidae: Megaloptera) along a Large River. Journal of Freshwater Ecology 9 57-62. Finally, the pupae emerge from the chamber, leaving behind the larval and pupal skins.

Uses

Hellgrammites are popular among anglers as bait due to their large size, endurance, and ferocious temperament.Contreras-Ramos, A. Corydalinae. Tree of Life Web Project. November 15, 1997. John Henry Comstock suggested securing a net or wire screen to the rocky bottom of a creek and disturbing the rocks just upstream of the screen as a method to catch the larvae. They often run for relatively high prices at bait shops, leading to over-exploitation in some areas and regulation of sale in certain states. Some anglers instead use lures in the shape of hellgrammites.Turpin, T
Dobsonflies Look Vicious.
Purdue Agriculture News Columns. Purdue Extension. August 8, 2013. Although not to the same extent as the larvae of mayflies and caddisflies, hellgrammites are intolerant of polluted waters and may have potential to be used as indicators of water quality.Gullan, P. J., and P. S. Cranston. The Insects: An Outline of Entomology. Hoboken, NJ: Wiley Blackwell, 2004. 260. As the adults are strongly attracted to lights, entomologists and collectors often use black light and mercury-vapor light traps to capture them.

Gallery

File: Protohermes grandis.jpg, '' Protohermes grandis'' File:Corydalus cornutus MHNT.jpg, ''

Corydalus cornutus The eastern dobsonfly, ''Corydalus cornutus'', is a large insect in the Corydalidae family. It is found in eastern North America in regions with fast-flowing streams where its aquatic larvae develop. These are known as hellgrammites and are amon ...

'' File:NevromusAustroindicus4.jpg, '' Nevromus austroindicus'' Image:Dobsonfly Corydalus cornutus larvae.jpg, ''

'' hellgrammite

References

External links

Aquatic Critters. Missouri Botanical Garden.
Genus ''Corydalus''
Tree of Life Web Project. 1997.

Featured Creatures. UF/ IFAS {{Taxonbar, from=Q2790845 Aquatic insects Corydalidae