Friday, May 29, 2015

Episode 268 (6-1-15): On the Bottom Underwater, It’s Chironomid Territory

CLICK HERE to listen to episode audio (3:47)

Transcript of audio, notes on the audio, photo, and additional information follow below. All Web addresses mentioned were functional as of 5-28-15.


From the Cumberland Gap to the Atlantic Ocean, this is Virginia Water Radio for the week of June 1, 2015.

This week, we feature another mystery sound.  Have a listen for about 15 seconds, and see if you can guess what kind of mostly-aquatic insect is making these sounds.  And here’s a hint: small, but with big impacts, there’s nothing “MIDdling” about these creatures—except part of their name.  

SOUND – 14 SEC – Buzzing of swarming non-biting midge adults, Blacksburg, Va., 5/13/15

If you guessed midges, you’re right!  Specifically, those were swarming adults of one species of non-biting midges, technically called chironomids [pronounced chi-ro-NOM-ids].  Chironomids’ immature forms—egg, larva, and pupa—develop in water; winged adults emerge from water to live only a few days or weeks to form mating swarms—as you heard—and to lay eggs.  Scientists classify chironomids as a family within the group of insects called “true flies,” which also includes mosquitoes, house flies, and many other familiar insects.  Chironomids aren’t as well-known as those everyday flies, but the family’s aquatic significance is huge.  With over 1000 species, chironomids are North America’s most diverse family of aquatic insects; they live on the bottom of all kinds of aquatic habitats, both freshwater and marine; and the number of individuals can reach the tens of thousands per square meter on the bottom of some water bodies, especially deep lakes.  These and other factors make chironomids a key component of aquatic food webs, as they eat small organisms and bottom debris and in turn are eaten by larger animals, including many kinds of fish.

Chironomids can also help indicate the health of aquatic systems, because certain species are tolerant of poor environmental conditions, such as low dissolved oxygen.  For example, bright red chironomids called “bloodworms” have blood hemoglobin that allows them to survive low dissolved oxygen.

On land, chironomid adults don’t bite humans or anything else, as the name “non-biting midges” indicates.  But dense mating swarms can sometimes create a human nuisance, such as in July 2010 near Baltimore, Maryland, where a large swarm led one person to claim that “Every leaf of every tree was covered with...midges.”  If you look underwater, you might be similarly impressed by nearly countless chironomids.

SOUND – ~1-2 SEC - Appomattox River underwater recording, 4/18/14.

For more Virginia water sounds, music, and information, visit us online at, or call us at (540) 231-5463.  Virginia Water Radio is produced by the Virginia Water Resources Research Center, part of Virginia Tech’s College of Natural Resources and Environment.  Thanks to Stewart Scales for his banjo version of Cripple Creek to open and close the show.  In Blacksburg, I’m Alan Raflo, thanking you for listening, and wishing you health, wisdom, and good water.

The sound of a swarm of non-biting midge adults was recorded on May 13, 2015, at a residential lawn in Blacksburg, Va.  Thanks to Eric Day, Virginia Tech Department of Entomology, for identifying a sample of these insects and for providing other information.

The underwater sound was recorded by Raven Harris on the Appomattox River on April 18, 2014.  Thanks to Mr. Harris for providing this sound.

Larvae of chironomid species sampled from Eastland Creek in Wise County, Va., in October 2012.  Specimens courtesy of Tony Timpano and Kriddie Whitmore, Virginia Tech Department of Forest Resources and ConservationPhoto by Eric Day, Virginia Tech Department of Entomology.
Adult of the chironomid species recorded for this episode.  The animal was captured from a swarm over a residential lawn in Blacksburg, Va., on May 13, 2015.  Photo by Eric Day, Virginia Tech Department of Entomology.

Here are some other bits of information about non-biting midges, family Chironomidae in the insect order Diptera (true flies).  The last name(s) of the sources for each item, with relevant page number(s), are listed in parentheses at the end of each item; for full source information, please see the Sources section below.

Species Diversity
The insect order of the true flies, known as Diptera, includes some 17,000 species in North America, making it second only to the order of beetles (Coleoptera) in the number of species, also referred to as its diversity.  Most true flies are terrestrial, but 29 families with about 3500 species in North America have aquatic larvae.  (Voshell, p. 396)

There are several other families of dipterans with “midge” in the common name.  The chironomid family has by far the largest number of species in North America, but the other families still have species with significant ecological and human impacts.  Other “midge” families include the biting midges (also called “no-see-ums” or “punkies”), dixid midges, mountain midges, net-winged midges, and phantom midges.  (Voshell, pp. 412-425)

Chironomid species may constitute as much as 50 percent of the species present in some communities of aquatic macroinvertebrates.  (Voshell, p. 421)

Modes of Living
Some chironomid species “roam freely,” but most construct tubes of fine particles of sediment and organic detritus, held together by silk.  Some attach these tubes to rocks, plants, logs, or other objects, but some species attach to other insects in a commensal relationship (commensalism is a type of symbiosis, in which one organism benefits but the other is not harmed).  (Voshell, p. 420)

As a group, chironomid larvae feed primarily by collecting or filtering organic material (plant debris, animal debris or wastes, decomposed materials) from the substrate or from water; some are predators.  (Voshell, p. 420-422)

Tolerance of Environmental Conditions
Because of the great diversity of species in this family, there’s a correspondingly great range of tolerance for various environmental conditions, such as temperature, dissolved oxygen, salinity, and chemical pollutants.  “In general [however], if midge larvae are very numerous and account for the majority [of individuals or species] in a community, that is an indication of poor environmental health caused by some type of pollution. ...Some kinds [of midges] are very tolerant of toxins, such as petroleum or heavy metals.”  (Voshell, p. 422)

Hemoglobin is found in the blood of other animals that live on the bottoms of water bodies (known as the benthic area or zone), but “[t]he bright red species of Chironomus [a chironomid genus] are especially characteristic....” (Cole, p. 66)

The ability of chironomids (as a group) to inhabit a very wide range of environmental conditions is “the product of a very wide array of morphological, physiological, and behavioral adaptations.”  An example of morphological (body structure) adaptations is “extreme variation” shown in mouthparts.  An example of physiological adaptation is hemoglobin in the blood of some species.  And behavioral adaptations include variations in the activities (timing, etc.) of the life stages of different species.  (Merritt and Cummins, pp. 551-552)


Used for This Episode

W.P. Coffman and L.C. Ferrington, Jr., “Chironomidae,” in R.W. Merritt and K.W. Cummins, eds., An Introduction to Aquatic Insects, 2nd Edition, Kendall/Hunt Publishing Company, Dubuque, Ia., 1984.

Gerald A. Cole, Textbook of Limnology (2nd Edition), C.V. Mosby Company, St. Louis, Mo., 1979.

J. Reese Voshell, Jr. Guide to Common Freshwater Invertebrates of North America, McDonald & Woodward Publishing, Blacksburg, Va., 2002.

Timothy Wheeler, Midge infestation in Back River a mystery, Baltimore Sun, 7/3/10.

For More Information about Non-biting Midges and Other Insects

P.D. Armitage, Peter Cranston, and L.C. Pinder, The Chironomidae: Biology and Ecology of Non-Biting Midges, Chapman and Hall, London, 1997, accessed online at

Iowa State University Department of Entomology, “BugGuide,” online at

McCafferty, W. Patrick, Aquatic Entomology: The Fishermen's and Ecologists' Illustrated Guide to Insects and Their Relatives, Jones and Bartlett Publishers, Toronto, 1998.

“Mosquitoes and Water,” Virginia Water Central, June 2009, pp. 6-15 (Virginia Water Resources Research Center, Blacksburg, Va.), online at

University of Florida Department of Entomology, “Featured Creatures” Web site,

Virginia Tech Department of Entomology Insect Identification Lab, online at

For previous episodes on aquatic insects, please see the “Insects” category at the Index link above (  In addition, Episode 81 (9/26/11) focuses on the use of aquatic insects in monitoring the quality of stream water and habitat.


This episode may help with the following Virginia’s 2010 Science Standards of Learning (SOLs).

Grades K-6 Earth Resources Theme
3.10 - impacts on survival of species.
4.9 - Va. natural resources, including watersheds, water resources, and organisms.

Grades K-6 Life Processes Theme
2.4 - life cycles.
3.4 - behavioral and physiological adaptations.

Grades K-6 Living Systems Theme
2.5 - living things as part of a system, including habitats.
3.5 - food webs.
3.6 - ecosystems, communities, populations, shared resources.
4.5 - ecosystem interactions and human influences on ecosystem.
5.5 - organism features and classification.
6.7 - natural processes and human interactions that affect watershed systems; Va. watersheds, water bodies, and wetlands; and water monitoring.

Life Science Course
LS. 4 - organisms’ features and classification.
LS.6 - ecosystem interactions, including cycles and energy flow.
LS.8 - community and population interactions, including food webs, niches, symbiotic relationships.
LS.9 - adaptations for particular ecosystems’ biotic and abiotic factors.
LS. 10 - changes over time in ecosystems, communities, and populations, and factors affecting those changes.
LS.11 - relationships between ecosystem dynamics and human activity.

Earth Science Course
ES.8 - freshwater resources, including groundwater, and influences by geologic processes and the activities of humans.

Biology Course
BIO.6 - bases for modern classification systems, including structures, biochemistry, and developmental stages.
BIO.8 - dynamic equilibria and interactions within populations, communities, and ecosystems; including analysis of the flora, fauna, and microorganisms of Virginia ecosystems.

Virginia’s SOLs are available from the Virginia Department of Education, online at