Hellgrammites

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Melissa Deluke

Hellgrammites (also known as toe biters or conniption bugs) are the larval form of the dobsonfly. The dobsonfly family is most abundant in Asia, but it is also found in North and South America, Africa, Australia, and New Zealand (Arnett, 1993). Hellgrammites belong to the kingdom Animalia, phylum Arthropoda, subphylum Mandibulata, and class Insecta. Within the class Insecta the dobsonfly is part of the order Neuroptera, family Corydalidae, and genus Cornutus (Encyclopedia Britannica Online, 2000).

Species within the order Neuroptera are generally characterized by complete holometabolous metamorphosis, with egg, larvae, pupae, and adult stages. All eggs, pupae, and adults are terrestrial (Evans, 1978), and the larvae are aquatic invertebrates who inhabit both lotic (flowing) or lentic (still) waters in tropical and temperate climates. The larvae are carnivores with incomplete digestive tracts and they dwell on the bottom of the body of water that they inhabit. The adults in this order found outside of the water near the larval habitat, they are weak flyers, and they have a glandular sensilla group near the abdominal apex (Henry, 1982).

The lifespan of the hellgrammite ranges from 2 to 5 years. This species is in its larval form as a hellgrammite for the majority of its life, for the pupal stage lasts for 2-4 weeks, and the adult stage only lasts for 1 to 2 weeks (Henry, 1982). The hellgrammite is usually found beneath rocks in cold, fast flowing, well-oxygenated streams, lakes, or rivers (Online 4). It passes through 10-12 instars and can be 35-65 mm in length at maturity. The hellgrammite has a pair of hooked prolegs where the abdomen ends (Henry, 1982), as well as three pairs of segmented legs on the mid section of the body (Online 7). It has short antennae and large pinching jaws, and it is thick-skinned and dark gray or black in color (Online 1). Respiration in the hellgrammite takes place through tracheal gills which are found at the base of the lateral filaments. It has 8 pairs of lateral filaments, and the gill tufts (which resemble fingerlike projections) are found on abdominal segments 1-7 (Evans, 1978). The feeding process for the hellgrammite is predacious due to their biting mouthparts which are strong and well-developed. They feed on aquatic insects, small fish, amphibians, or any small invertebrate that is a bottom dweller. Among the organisms that they will prey upon, their main preferences are black fly larvae and net spinning caddisflies (Online 1).

When preparing for pupation, the hellgrammite emerges from the water and quickly moves across the earth’s surface. It typically does not travel a great distance from the waters edge, but sometimes it will venture as far as 50 meters from shore (Pennak, 1978). It only travels during the night when searching for a place to pupate, because it hides under rocks or logs during the day (Howard, 1908). Sometimes it will burrow 5-10 cm into the ground to pupate, but typically it can be found in a chamber in any damp area beneath rocks, logs, or debris (Pennak, 1978). Unlike other members of the order Neuroptera, hellgrammites do not form a cocoon or a woven structure around themselves in the pupal stage (Concise Encyclopedia of Biology, 1996). The length of the pupa ranges from 30-60 mm, it is light yellow in color, and it is able to walk and defend itself due to its free appendages and strong biting mandibles (Henry, 1982).

 

The adult dobsonfly usually emerges from the pupal stage during the month of June (Howard, 1908). It lives outside of the water near the stream, lake, or river that was inhabited by the hellgrammite. It is 4-7 cm in length, it has a wingspan ranging from 13-16 cm, and its forewings are longer than its hind wings (Borror, 1970). There are no specific modifications of the wings or legs in the adult stage, therefore their flight is weak and fluttery and they do not walk well. They are pale yellow or brownish black in color and they have filiform, moniliform, or pectinate antennae. The antennae, as well as the mandibles, are more elaborate in males than in females (Henry, 1982). Due to the highly structured antennae and mandibles of the male species the dobsonfly shows sexual dimorphism. The mandibles of the male are sharp and pointed and can be 3 times as long as the head. Because of this, humans may encounter a dobsonfly and think it’s fierce and dangerous but in actuality it is harmless (Borror, 1970). Although mandibles are mouthparts, the dobsonfly does not use them to eat because feeding does not occur in the adult stage (Henry, 1982). The male uses the mandibles during the mating process when capturing, prodding, and caressing the female (Arnett, 1993), and they are also used when males fight one another (Evans 1972, as cited by Online 1). Prior to mating the male will flutter his wings, and both males and females will touch antennae. During mating the female dobsonfly is fertilized by the transfer of a gelatinous spermatophor (Hayashi 1992, 1993 as cited by online reference 1). The female dobsonfly lays her eggs in chalky white clusters that are approximately the size of a nickel (Howard, 1908). The clusters can be made up of one, two, three, four, or five layers, they are rounded or squared, and they contain 300 to 3000 eggs. They are deposited on anything that protrudes over the water, such as rocks, trees, piers, or bridges (Henry, 1982). The eggs are laid in such locations in order to allow the first instar larvae to drop into the water below and begin life as a hellgrammite. Of the locations mentioned, the female dobsonfly does not appear to prefer to lay her eggs in one place over another, however, the egg masses of the dobsonfly are similar in appearance to those of Chloronia and Platyneuromus, and as a result, it is difficult to find preference patterns for egg placement between these species (Online 1). Each individual egg is about 1.3 mm long with a knobbed bulge projecting off the side (Evans, 1978). The eggs hatch at night, usually after the air temperature has been cool for about one week (Online 4).

Although hellgrammites will bite humans they are significant for human use. The gill tufts of the hellgrammite are appealing to fish because they resemble fringe (Online 6). Therefore, fishermen like these organisms because they are good bait for bass and trout. Not only are fish caught when this bait is used, but hellgrammites are easy to utilize as well, for they survive on wet moss for days and their tough exterior holds them together on a hook (Pennak, 1978). An additional attribute of hellgrammites is their intolerance of water pollution, making them good indicators of water quality (Encyclopedia Britannica Online, 2000).

The hellgrammite is an interesting aquatic invertebrate, for it goes through many stages of life, and its behavior in each stage is dramatically different. The majority of the lifespan is spent in the larval form where the hellgrammite is fierce and predacious, has good mobility, and can be utilized by humans. In contrast, the pupa lasts for a short period of time and it will not move or bite unless provoked to do so. The adult form of this species is short-lived as well, but it does not bite, feed, or move skillfully. The dobsonfly bears no direct significance to humans, however, it has an indirect impact because it will reproduce and create larvae which humans can use.

 

 

References

Arnett, R. H., Jr. 1993. A Handbook of the Insects of America North of Mexico.

The Sandhill Crane Press, Inc. Gainseville, FL. 249 p.

Borror, D. J. and R. E. White. 1970. A Field Guide to the Insects of America North of

Mexico. Houghton Mifflin Company, Boston. 141 p.

Concise Encyclopedia of Biology. New York: Walter de Gruyter & Co., 1996.

Encyclopedia Britannica online: Dobsonfly and Neuropteran. Accessed October 2, 2000.

Evans, E. D. 1978 Megaloptera and Aquatic Neuroptera. Pages 133-146 in R. W.

Merrit and K. W. Cummins (eds.). An Introduction to Aquatic Insects of

North America. Kendall/Hunt Publishing Company. Dubuque, Iowa.

Henry, C. S. 1982 Neuroptera. Pages 470-472 in S. P. Parker (ed.). Synopsis

and Classification of Living Organisms. McGraw-Hill, Inc. New York.

Howard, L. O. 1908. The Insect Book. Page & Company, New York. 211 p.

Lutz, P. E. 1986. Invertebrate Zoology. Greensboro Addison-Wesley Publishing

Company, Ontario. 554p.

Online 1. Available:

http://ag.arizona.edu/tree/eukaryotes/animals/arthoropoda/hexapoda/megalo…/

megaloptera.htm October 20, 2000.

Online 2. Available:

http://encarta.msn.com/find/Concise.asp?ti=0487B000 October 20, 2000.

Online 3. Available:

http://osfl.gmu.edu/~avia/corydalid.htm October 20, 2000. 

Online 4. Available: http://www.chebucto.ns.ca/Science/SWCS/ZOOBENTH/megalopt.html

October 20, 2000.

Online 5. Available:

http://www.cnr.berkeley.edu/citybugs/Taxa/Megaloptera/Coryda…/

FamilyCorydalidaePage.htm October 20, 2000.

Online 6. Available:

http://www.newton.dep.anl.gov/natbltn/300-399/nb397.htm October 20,2000.

Online 7. Available:

http://www.tier.net/riverwatch/dobfly.htm October 20, 2000.

Pennak, R. W. 1978. Freshwater Invertebrates of the United States 2nd edition. John

Wiley & Sons. New York.