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Order Raphidioptera - Snakeflies

Is this snake fly Agulla? - Agulla - female Reality Check: Is this snake fly Agulla? - Agulla - male Snakefly (Raphidiidae) - Agulla - female Square-headed Snakeflies (Inocelliidae), Negha - Negha - female Snakefly - Agulla - female Kila mystery bug - Agulla Snakefly - Agulla - female Snakefly female dead front - Negha meridionalis - female
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Raphidioptera (Snakeflies)
Synonyms and other taxonomic changes
Formerly Raphidioidea, a suborder of Neuroptera.
Numbers
Two families: Raphidiidae, with two Nearctic genera (Agulla and Alena) and 18 species; and Inocelliidae, with one Nearctic genus (Negha) having three species (1).
Identification
Snakefly larvae are much longer than wide and are rather flattened. The head and 1st thoracic segment are smooth, more scleroterized, and generally darker and more uniformly colored than the 2nd & 3rd thoracic and abdominal segments...the latter often having a mottled color patterning. The abdominal segments, though more or less flat, typically have a "puffy" membranous look, and are edged on both sides by a thinned, mildly rounded flange. Larvae of the family Raphidiidae have seven simple eyes on each side of the head; while those of the family Inocelliidae have four...two of which are very minute [pg. 137, Carpenter, 1936].
Snakefly larvae can be confused with campodeiform beetle larvae (though snakefly larvae appear to lack the terminal appendages of many such beetle larvae, see this post).


Adults are similar to Neuroptera but with elongated prothorax (or "neck") giving rise to their unique "snake-like" appearance. No modification of front legs as in Mantispidae.
Female snakeflies can be easily distinguished from the males by the presence of a conspicuously long and flexible ovipositor, sometimes mistaken as a "tail" or "stinger".
female male
Note, however, that snakeflies do not sting and are harmless to humans.

According to this reference, as well as Borror & Delong(2), the two families of Raphidioptera can be distinguished (at least in North America) as follows:
1. Head with ocelli; forewing with pterostigma bisected by a veinlet...........Raphidiidae
1'. Head without ocelli; forewing with pterostigma not bisected by a veinlet.....Inocelliidae
While the ocelli are rarely discernable in photos, the pterostigma (= tinted "wing-spots") are usually apparent.

Also, while seemingly unmentioned in many keys, the shape of the head (seen dorsally) seems to be a fairly good discriminant between the two families. Members of Inocelliidae (i.e. genus Negha in North America) are called "square-headed snakeflies" and have decidedly rectangular heads with fairly parallel sides. Members of Raphidiidae, on the other hand, tend to have more "kite-shaped" heads, which tend to taper more visibly from widest near the middle to thinner at the posterior end. For instance, compare the following:
Inocelliidae (Genus Negha) vs. Raphidiidae (Genus Agulla)
Admittedly, there can be cases where the (dorsal) head shape appears intermediate between the extremes of parallel-sides vs. "kite-shaped", which may be why this character doesn't always appear in keys. But it does seem to work when one of the two shapes are clearly discernible.
Range
In North America (north of Mexico) snakeflies mostly occur to the west of the Rockies.
Habitat
According to noted raphidiopterist Horst Aspöck (see [Aspöck, 2002] under "Internet References" below):
All Inocelliidae, and (likely the smaller) part of the Raphidiidae, probably develop under bark. The majority of Raphidiidae have larvae that live in superficial layers of soil, particularly in the detritus around the roots of shrubs, possibly sometimes even in crevices of rocks.
Snakeflies are confined to arboreal habitats in the broadest sense, including all types of forests, macchias and even biotopes with scattered shrubs. In the northern temperate zones they occur from sea level up to timberline.
[Note: "Macchias" is an Italian word roughly equivalent to the word "chaparral"...though it can also carry a connotation of habitat disturbed by human impacts.]
Food
Both larvae and adults are predatory, though they are capable of catching and killing only small and weak prey. Snakefly larvae feed on eggs and larvae of various insects, as well as adults of minute arthropods (e.g. mites, springtails, barklice, and homopterans). Adults typically prefer aphids but may eat a wide variety of arthropods. Adults take efforts to clean themselves after feeding. Females have been observed to "have a curious habit of frequently wagging their ovipositor during the process of eating, as though expressing satisfaction with the food." [pg. 104, Carpenter, 1936]
Life Cycle
Holometabolous. The following details are from [Aspöck, 2002]:
The egg stage lasts from a few days up to 3 weeks.
The larval period lasts at least one year, and in most species two or three years. Under experimental conditions, some individuals of some species have had larval periods of up to six years. The number of larval instars is not fixed, it varies around 10–11, but may reach 15 or even more.
The prepupal stage is always a short period of a few days duration only.
Pupation (usually) takes place in spring, and lasts from a few days up to about 3 weeks. In very few species (genus Alena, Mexican inocelliid species) pupation takes place in summer and, after a pupal stage of a few weeks, the adults hatch in late summer. It's believed all snakeflies need a period of low temperature (probably around 0°C) to induce pupation or hatching of the imago.
Remarks
Snakefly larvae have the unusual abliliy to scurry rapidly both forward and in reverse! (See this video by BugGuide contributor Sean McCann.).
Although adult females appear to have a long "stinger", snakeflies do not sting and are harmless to humans. In fact, they are thought to be beneficial as predators of forest pests.
The order Raphidioptera is an ancient, relict group. Some quotes from Aspöck on origins:
"Phylogenetic results indicate that the Raphidioptera of America derive from a Mesozoic fauna established before the separation of South America from Africa and the break-up of Laurasia. This fauna was much richer than the extant one, and snakeflies also occurred in tropical climates and in the Southern hemisphere. It is hypothesized that, due to the extraterrestrial impact at the end of the Cretaceous, 65 million years ago, all lines adapted to tropical climates became extinct and only those adapted to cold climates (Raphidiidae, Inocelliidae) survived." [Aspöck, 1998]
"The extant snakeflies are the remaining – and apparently far distant – twigs of many more branches of earlier geological periods: the Mesozoic biodiversity of the Raphidioptera was indeed much richer" [Aspöck, 2002]
A discussion of the evolutionary history of Raphidioptera can also be found in this (4+ page) passage from Grimaldi & Engel (3)
For the very ambitious, a potential resource for identifying the snakeflies on BugGuide to species is the worldwide treatment (in German):
ASPÖCK, H., ASPÖCK, U. & RAUSCH, H. (1991) Die Raphidiopteren der Erde. Eine monographische Darstellung der Systematik, Taxonomie, Biologie, Ökologie und Chorologie der rezenten Raphidiopteren der Erde, mit einer zusammenfassenden Übersicht der fossilen Raphidiopteren (Insecta: Neuropteroidea). Goecke & Evers, Krefeld, Volume 1: 730 pages, Volume 2: 550 pages.
See Also
Related groups in Superorder Neuropterida:
Megaloptera - Alderflies, Dobsonflies, and Fishflies
Raphidioptera - Snakeflies
Neuroptera - Antlions, Lacewings and Allies
Print References
Arnett, p. 346 (1)
Aspöck, H., U. Aspöck, and H. Rausch. (1991) Die Raphidiopteren der Erde. Goecke & Evers Verlag, Dürerstrasse 13, D-4150 Krefeld, Germany. 1648 DM. Volume 1, 730 pages. Volume 2, 550 pages, with 3065 illustrations and 206 distribution maps.
Aspöck, H. 1998: Distribution and biogeography of the order Raphidioptera: updated facts and a new hypothesis. — Acta Zool. Fennica 209: 33–44.
Carpenter, F, M. (1936) Revision of the Nearctic Raphidiodea (Recent and Fossil). Proc. Amer. Acad. Arts & Sci., 71: 89-157.
Grimaldi & Engel (3)
Internet References
Informative entry for snakeflies at Answers.com website.
Video clip by Sean McCann showing the interesting locomotion of a snakefly larva.
Video clip of adult Agulla snapping at a small rod, drinking water, and eating small prey.
The Biology of Raphidioptera: A Review of Present Knowledge (PDF, 16 pages) by H. Apsöck (2002).
ubc.ca Biodiversity Checklist of the Raphidioptera of British Columbia.
A snakefly webpage at Washington State University.
Tree of Life Web--Raphidioptera
Works Cited
1.American Insects: A Handbook of the Insects of America North of Mexico
Ross H. Arnett. 2000. CRC Press.
2.Borror and DeLong's Introduction to the Study of Insects
Norman F. Johnson, Charles A. Triplehorn. 2004. Brooks Cole.
3.Evolution of the Insects
David Grimaldi and Michael S. Engel. 2005.