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 botanical subfamily names with "-oideae", and zo ...

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

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) "wi ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Corydalidae. The

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

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 strea ...

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

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

of dobsonflies are distributed in the

Americas The Americas, sometimes collectively called America, are a landmass comprising the totality of North America and South America.''Webster's New World College Dictionary'', 2010 by Wiley Publishing, Inc., Cleveland, Ohio. When viewed as a sing ...

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

, and

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

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. Career Comstock w ...

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 ( ) or lepidopterans is an order of winged insects which includes butterflies and moths. About 180,000 species of the Lepidoptera have been described, representing 10% of the total described species of living organisms, making it ...

insects of temperate zones such as the United States and Canada, with a wingspan of up to in some species of '' Corydalus''.Stange, Lionel. "Alderflies and Dobsonflies." Encyclopedia of Entomology. 2nd ed. New York: Springer Publishing, 2008. The Asian '' Acanthacorydalis fruhstorferi'' 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 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. 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 A secondary sex characteristic is a physical characteristic of an organism that is related to or derived from its sex, but not directly part of its reproductive system. In humans, these characteristics typically start to appear during puberty ...

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 or committed romantic, ''de facto'' relationship. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marri ...

. 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 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 is distinguished from closely related

clades In biology, a clade (), also known as a monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach to taxonomy ...

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 ...

(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 (from Ancient Greek ἔντομον (''éntomon''), meaning "insect", and -logy from λόγος (''lógos''), meaning "study") is the branch of zoology that focuses on insects. Those who study entomology are known as entomologists. In ...

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 a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

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 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 Northwest India is a loosely defined administrative divisions of India, region of India. In modern-day, it consists of north-western states of the India, Republic of India. In historical contexts, it refers to the northwestern Indian subcontin ...

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 '' Corydalus'', 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 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 order ...

caddisflies The caddisflies (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 basis ...

, stoneflies, and

chironomid Chironomidae , commonly known as non-biting midges or chironomids , are a family of Nematoceran flies with a global distribution. They are closely related to the families Ceratopogonidae, Simuliidae, and Thaumaleidae. Although many chironomid s ...

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 grou ...

, an indicator additive in natural gas and propane, and may behave as an animal sentinel in the presence of these gases.

Life cycle

The

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

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 clade Holometabola. Immatur ...

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, also known as a reproductive organ, is a part of an organism that is involved in sexual reproduction. Sex organs constitute the primary sex characteristics of an organism. Sex organs are responsible for producing and transporting ...

a large, globular

spermatophore A spermatophore, from Ancient Greek σπέρμα (''spérma''), meaning "seed", and -φόρος (''-phóros''), meaning "bearing", or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especiall ...

about 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 typica ...

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 ...

masses containing on average one thousand grey, cylindrical eggs, each egg about long and 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. The ...

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, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...

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 (; : 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 life cycle, the stages th ...

. 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 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

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

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.

Smallmouth bass The smallmouth bass (''Micropterus dolomieu'') is a species of freshwater fish in the Centrarchidae, sunfish family (biology), family (Centrarchidae) of the order (biology), order Centrarchiformes. It is the type species of its genus ''Micropterus ...

, in particular, are very attracted to hellgrammites as bait, due to the insects' active movement in the water.https://www.nps.gov/neri/learn/nature/hellgrammites.htm

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 Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...

.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 A blacklight, also called a UV-A light, Wood's lamp, or ultraviolet light, is a lamp (fixture), lamp that emits long-wave (UV-A) ultraviolet light and very little visible light. One type of lamp has a violet light filter, filter material, eith ...

and mercury-vapor light traps to capture them.

Gallery

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