Megaloptera

(invertebrate zoology) A suborder included in the order Neuroptera by some authorities.

(Dobsonflies, fishflies, and alderflies)

Class: Insecta

Order: Megaloptera

Number of families: 2

Evolution and systematics

The oldest known fossils of Megaloptera date from the Permian. The Megaloptera are often considered to be the most primitive group of endopterygote (with internal development of wings as imaginal discs in the larvae) insects. The order Raphidioptera constitutes their sister group, and together with Neuroptera they form the monophyletic group of the Neuropterida. Megaloptera includes only two families, Corydalidae and Sialidae (alderflies). Corydalidae, in turn, comprises two subfamilies, Corydalinae (dobsonflies and hellgrammites) and Chauliodinae (fishflies), which are considered families by some authors.

Physical characteristics

Adult alderflies range from 0.4 to 0.6 in (10–15 mm), and dobsonflies range from 1.6 to 2.4 in (40–60 mm); larvae reach a maximum length of 1 in (25 mm) and 1.2–2.6 in (30–65 mm), respectively. Adults are soft-bodied insects, black, brown, or yellowish orange to dark green in color. They possess filiform, moniliform, or pectinate antennae and large compound eyes, and they either have (Corydalidae) or lack (Sialidae) ocelli. They have two pairs of membranous wings with a complex nervelike pattern of veins, although longitudinal veins are not branched near the wing margin. The hind wings are broader at the base than the front wings, and this enlarged anal area is kept folded like a fan at rest. Larvae are elongated, flattened, and prognathous, with chewing mouth-parts. They have seven or eight lateral pairs of abdominal gills. In sialids the abdomen ends in a median unsegmented filament, whereas in corydalids it terminates in a pair of anal prolegs. Pupae have free appendages that are not fastened to the body and are not enclosed in a cocoon.

Distribution

They occur in the New World, South Africa, Madagascar, and Asian and Australian regions and are most diverse in temperate regions, with fewer species in the tropics.

Habitat

Larvae are aquatic, inhabiting both lentic (still water) and lotic (moving water) environments, including streams, spring seeps, rivers, lakes, ponds, swamps, and even temporarily dry streambeds. They burrow into soft substrate or in crevices or hide under stones or bark. Eggs, pupae, and adults are terrestrial. Eggs can be found in masses on leaves, branches, rocks, and bridges overhanging the aquatic habitat. Pupae are found in the shoreline soil and litter adjacent to the larval habitat, and adults are found in the same general area where larvae live.

Behavior

Adults seldom are seen in large numbers because they are short-lived and secretive. Sialids are active during the warm midday hours, engage infrequently in brief flights, and can be found resting near their larval habitats with the wings held rooflike over the abdomen. Most corydalids have nocturnal habits and are attracted to light, although there are some diurnal species. Their flight is slow and irregular, but some may fly considerable distances. At rest they keep the wings flat over the abdomen.

Feeding ecology and diet

Larvae are entirely predaceous, feeding nonselectively on a wide variety of small aquatic invertebrates, such as insect larvae, crustaceans, mollusks, and annelids. Adults apparently do not feed.

Reproductive biology

Communication between sexes before mating is known to occur in some sialids and corydalids. Corydalus species show sexual dimorphism; males have very long mandibles with which they duel with each other and prod the female. Copulation takes place in vegetation near the water. Females deposit masses of one to five layers of 200 to 3,000 eggs on objects overhanging the water, in locations protected from insolation during the hottest part of the day. After opening the egg with an egg burster, the larvae drop to the water after hatching, where they undergo 10 to 12 molts. Fully grown larvae leave the water and pupate in an unlined chamber in the soil or litter. Adults usually emerge from late spring to midsummer. Life cycles range from one to five years.

Conservation status

About 300 species of megalopterans have been described, none of which is listed by the IUCN. Some species with restricted distributions in small rivers and streams probably are sensitive to deforestation, pollution, and eutrophication (involving depletion of oxygen that is normally taken from the water by aquatic larvae) and could be potential candidates for conservation programs.

Significance to humans

Larvae are important predators in aquatic food chains. Some species are economically important as trout food, and their larvae are used as fish bait (i.e., Archichauliodes diversus from New Zealand). In the Japanese tradition, dried larvae of some dobsonflies are believed to be a remedy for emotional problems in children.

Species accounts

Resources

Brigham, W. U. "Megaloptera." In Aquatic Insects and Oligochaetes of North and South Carolina, edited by A. R. Brigham, W. U. Brigham, and A. Gnilka. Mahomet, IL: Midwest Aquatic Enterprises, 1982.

Chandler, H. P. "Megaloptera." In Aquatic Insects of California, edited by R. L. Usinger. Berkeley: University of California Press, 1956.

Contreras-Ramos, A. Systematics of the Dobsonfly Genus Corydalus Latreille (Megaloptera: Corydalidae). Thomas Say Monographs. Lanham, MD: Entomological Society of America, 1998.

Evans, E. D., and H. H. Neunzig. "Megaloptera and Aquatic Neuroptera." In An Introduction to Aquatic Insects of North America, edited by R. W. Merritt and K. W. Cummins. 3rd. edition. Dubuque, IA: Kendall/Hunt Publishing Company, 1996.

Henry, C. S., N. D. Penny, and P. A. Adams. "The Neuropteroid Orders of Central America (Neuroptera and Megaloptera)." In Insects of Panama and Mesoamerica, edited by D. Quintero and A. Aiello. Oxford: Oxford University Press, 1992.

Penny, N. D. "Neuroptera." In Aquatic Biota of Tropical South America. Part 1, Arthropoda, edited by S. B. Hurlbert, G. Rodríguez, and N. Dias dos Santos. San Diego: San Diego State University, 1981. ——. "Neuroptera." In Aquatic Biota of Mexico, Central America and the West Indies, edited by S. B. Hurlbert and A. Villalobos-Figueroa. San Diego: San Diego State University, 1982.

Contreras-Ramos, A. "Mating Behavior of Platyneuromus (Megaloptera: Corydalidae), with Life History Notes on Dobsonflies from Mexico and Costa Rica." Entomological News 110 (1999): 125–135.

Davis, K. C. "Sialididae of North and South America." New York State Museum Bulletin 68 (1903): 442–486, 499.

Stewart, K. W., G. P. Friday, and R. E. Rhame. "Food Habits of Hellgrammite Larvae, Corydalus cornutus (Megaloptera: Corydalidae), in the Brazos River, Texas." Annals of the Entomological Society of America 66 (1973): 959–963.

[Article by: Natalia von Ellenrieder, PhD]

The noun has one meaning:

Meaning #1: in some classifications considered a separate order: alderflies; dobsonflies; snake flies
  Synonym: suborder Megaloptera

Megaloptera Fossil range: Permian–Recent PreЄ Є O S D C P T J K Pg N
Alderfly of the genus Sialis
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Hexapoda
Class:	Insecta
Subclass:	Pterygota
Infraclass:	Neoptera
Superorder:	Endopterygota or Neuropterida (see text)
Order:	Megaloptera
Families
Corydalidae Sialidae and see text

Megaloptera is an order of insects. It contains the alderflies, dobsonflies and fishflies, and there are about 300 known species.

The Megaloptera 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^[1]. 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. Within the endopterygotes, the closest living relatives of the neuropteridan clade are the beetles.

The order's name comes from Ancient Greek - from mega- (μέγα-) "large" + pteryx (πτέρυξ) "wing" -, in reference to the large, clumsy wings of these insects. Megaloptera are relatively unknown insects across much of their range, due to the adults' short lives, the aquatic larvae's tolerance to pollution which is often rather high (so they are not often encountered by swimmers etc), and the generally crepuscular or nocturnal habits. However, in the Americas the dobsonflies are rather well-known, as their males have tusk-like mandibles. These, while formidable in appearance, are relatively harmless to humans, as well as all other organisms; much like a peacock's feathers they serve no purpose other than to impress females, and in addition to hold them during mating. Hellgrammites, which are dobsonfly larvae, are often used for angling bait in North America.

Contents 1 Anatomy and life cycle 2 Evolution 3 Footnotes 4 References

Anatomy and life cycle

Adult Megalopterans closely resemble the lacewings, except for the presence of a pleated region on their hind wings, helping them to fold over the abdomen. They have strong mandibles and mouthparts apparently adapted for chewing, although many species do not eat as adults. They have large compound eyes, and, in some species, also have ocelli. The wings are large and subequal.^[2]

The female lays thousands of eggs in a single mass, placing them on vegetation overhanging water. 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, and their aquatic larvae dwell in fresh water, around which the adults also live. The larvae are carnivorous, possessing strong jaws that they use to capture other aquatic insects. They have large heads and elongated bodies. The abdomen bears a number of fine tactile filaments, which, in some species, may include gills. The final segment of the abdomen bears either a pair of prolegs, or a single, tail-like appendage.^[2]

The larvae grow slowly, taking several years to reach the last larval stage. When they reach maturity, the larvae crawl out onto land to pupate in damp soil or under logs. Unusually, the pupa is fully motile, with large mandibles that it can use to defend itself against predators. The short-lived adults emerge from the pupa to mate - many species never feed as adults, living only a few days or hours.^[2]

Evolution

Apart from the two living families, there are a few prehistoric taxa in the Megaloptera, only known from fossils. Some of these occupy a more basal position:^[3]

• Genus Corydasialis (sometimes considered monotypic family Corydasialidae^[4])
• Family Parasialidae (probably paraphyletic)
• Family Euchauliodidae

Footnotes

1. ^ Also called "Neuropteroidea", though the ending "-oidea" is normally used for superfamilies. See references in Haaramo (2008).
2. ^ ^{a b c} Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed.. Oxford University Press. pp. 441–443. ISBN 0-19-510033-6. 
3. ^ See references in Haaramo (2008)
4. ^ Engel & Grimaldi (2007)

References

Wikimedia Commons has media related to: Megaloptera

• Grimaldi, David & Engel, Michael S. (2005): Evolution of the Insects. Cambridge University Press. ISBN 0-521-82149-5
• Engel, Michael S. & Grimaldi, David A. (2007): The neuropterid fauna of Dominican and Mexican amber (Neuropterida, Megaloptera, Neuroptera). American Museum Novitates 3587: 1-58. PDF fulltext
• Haaramo, Mikko (2008): Mikko's Phylogeny Archive: Neuropterida. Version of 2008-MAR-11. Retrieved 2008-MAY-05.

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