Introduction
The shimmering metallic green of a fly buzzing around waste or decaying matter might be off-putting to many, but these insects, often recognized as A Green Fly, play a crucial role in our ecosystems and even in human health. Specifically, the common green bottle fly, scientifically known as Lucilia sericata, is a ubiquitous species with a global presence. Belonging to the blow fly family Calliphoridae, this insect, like its relatives, is far more than just a nuisance. Lucilia sericata is remarkably significant in diverse fields, ranging from the intricacies of forensic science to groundbreaking medical treatments and the challenges of veterinary care. In the realm of forensics, the larvae, commonly called maggots, of this green fly are invaluable tools for estimating the post-mortem interval, a critical factor in criminal investigations. In medicine, these same maggots are employed in a therapy to combat stubborn infections, offering hope when conventional treatments fail. However, in veterinary science, the larvae of L. sericata can be detrimental, causing significant economic losses in livestock production.
Figure 1. Common green bottle flies, Lucilia sericata, attracted to dog feces. These green flies are common scavengers and can be found in various environments. Photograph by Whitney Crenshaw, Colorado State University, Bugwood.org.
Synonymy
The scientific classification of insects can be complex, and the green fly Lucilia sericata is no exception. Over time, this species has been identified and named under various synonyms, reflecting the evolving understanding of insect taxonomy. Some of the alternative names for Lucilia sericata include:
- Lucilia barberi Townsend, 1908
- Lucilia giraulti Townsend, 1908
- Lucilia sayi Jaennicke, 1867
- Musca sericata Meigen, 1826
- Phaenicia sericata Meigen, 1826
These synonyms highlight the history of research and classification surrounding this common green fly, eventually converging on the currently accepted name, Lucilia sericata (Meigen).
Distribution
Globally distributed, the green fly Lucilia sericata thrives in a wide range of environments. Its primary distribution is considered Holarctic, meaning it is predominantly found across the Northern Hemisphere, including widespread populations throughout the United States and southern Canada. However, its adaptability has allowed it to expand its range significantly. Today, L. sericata is also commonly found in Australia, as well as several countries in South and Central America. In Australia, this green fly, often referred to as the sheep blow fly due to its impact on livestock, is more prevalent in coastal regions and areas with higher humidity. This distribution pattern underscores the adaptability of Lucilia sericata to diverse climates and geographical locations.
Description
Identifying a green fly like Lucilia sericata requires attention to specific physical characteristics across its life stages, from adult to egg, larva, and pupa.
Adults
The adult common green fly is visually striking, primarily due to its metallic sheen. Adults typically exhibit a vibrant metallic green color, though some may lean towards a copper-green hue. A key identifying feature is their yellow mouthparts. The body of the adult green fly is hairy on the back and measures approximately 8–10 mm in length. The squamae, small lobes at the base of the wings, are noticeably hairless, which is another diagnostic characteristic.
Figure 2. Dorsal view of Lucilia sericata, showcasing the metallic green body and hairy back, key features for identifying this green fly. Photograph by Joseph Berger, Bugwood.org.
Figure 3. Ventral view of Lucilia sericata, highlighting the underside of this green fly and its anatomical details. Photograph by Joseph Berger, Bugwood.org.
Figure 4. Anterior-lateral view of Lucilia sericata, providing a different perspective on the physical characteristics of this green fly species. Photograph by Joseph Berger, Bugwood.org.
Eggs
The eggs of L. sericata, the green fly, are small and elongated, approximately 1.5 mm in length. Their color typically ranges from white to a pale yellow. Females often deposit eggs in clusters or masses, strategically placing them on food sources for the emerging larvae. One end of the egg is slightly tapered, a subtle detail in their morphology.
Figure 5. Female Lucilia sericata laying eggs. This image shows the ovipositor, the egg-laying organ, of this green fly, and the clustered egg deposition behavior. Photograph by Susan Ellis, Bugwood.org.
Larvae
The larval stages of this green fly, often referred to as maggots, are smooth and conical in shape throughout all three instars (developmental stages). Larvae are characterized by a complete peritreme on their posterior spiracles. Spiracles are respiratory structures located at the rear of the larvae. The larvae are white or yellowish in color and can grow to 12–18 mm in length before they pupate. Identifying blow fly larvae to species level can be challenging and usually requires microscopic examination and often confirmation through rearing to the adult stage.
Figure 6. Late instar larva of a Lucilia species. While this image represents a Lucilia larva, it provides a general view of the larval stage of a green fly maggot. Head is at the bottom of the image. Photograph by Richard Major, © Australian Museum. Used with permission.
Pupae
The pupal stage of the green fly Lucilia sericata is encased in a hardened puparium. This protective shell is formed from the skin of the last larval instar and is typically reddish-brown, light brown, or black. Pupae are oval in shape, measuring 9–10 mm in length and 3–4 mm in width. Initially, the pupal case is white but quickly darkens within hours as it hardens and matures.
Figure 7. Pupae of a Lucilia species. This image illustrates the pupal stage of a Lucilia green fly, showing the hardened puparium. Photograph by Richard Major, © Australian Museum. Used with permission.
Life Cycle
The life cycle of a green fly like Lucilia sericata is temperature-dependent, influencing the duration of each developmental stage. At approximately 21°C (70°F), eggs hatch in about 21 hours, while at a warmer 27°C (81°F), hatching occurs in approximately 18 hours after being laid. Larval development, encompassing three instars, takes about four days at 20°C (68°F) and reduces to three days at 27°C. Factors such as food source and humidity also significantly impact larval development rates. Once mature, the third instar larvae leave their food source to pupate in the surrounding soil or substrate. Pupal development lasts approximately 10 days at 21°C and seven days at 27°C, after which the adult green fly emerges. Adult females can lay clusters of up to 200 eggs at a time on a suitable host or carcass, and multiple generations can occur within a year, depending on environmental conditions.
Forensic Importance
Lucilia sericata, the common green fly, holds significant importance in forensic science, primarily in estimating the minimum post-mortem interval (PMI). These insects are often among the first to colonize a corpse after death. Blow flies like L. sericata, along with flesh flies and filth flies, are considered crucial for providing accurate PMI estimations. Remarkably, Lucilia sericata has been observed to lay eggs even in cool nocturnal conditions, a deviation from the typical daytime egg-laying behavior of most blow flies. This unusual behavior, though uncommon, can occur shortly after sunset, particularly when artificial lights are present and attract flies to a corpse.
The most common method for PMI estimation using green fly larvae involves determining the larval developmental stage at the time of discovery. While generally accurate, this method can be influenced by various environmental and biological factors that affect larval growth rates. Advanced techniques, such as gene expression analysis, are being developed to provide more precise age estimations of larvae, leading to more accurate minimum PMI determinations in forensic investigations.
Medical and Veterinary Importance
Beyond forensics, Lucilia sericata, this seemingly simple green fly, has surprising medical applications. Maggot therapy, using L. sericata larvae, is an increasingly recognized treatment for chronic wounds that resist conventional healing methods. In this therapy, sterile L. sericata larvae are applied to a wound under medical supervision. They selectively consume necrotic (dead) tissue and bacteria, effectively cleaning the wound and promoting the growth of healthy tissue. The larvae also secrete antimicrobial enzymes, further aiding in infection control. Patients typically experience minimal pain during maggot therapy. Concerns about wound contamination have been mitigated by the use of sterile maggots, eliminating the risk of microorganism transmission.
However, Lucilia sericata and its close relative Lucilia cuprina are notorious in veterinary medicine, particularly in Britain and Australia, as the primary causes of sheep strike. Hence, L. sericata is sometimes referred to as the sheep blow fly. Sheep strike, or blowfly strike, is a form of myiasis where fly larvae infest living tissue. It commonly occurs around the rear of sheep, attracted by fecal matter and urine-soaked wool. This condition is severe and can be fatal to sheep if left untreated, causing significant economic losses in sheep farming.
Figure 8. Adult Australian sheep blow fly, Lucilia cuprina. While Lucilia cuprina is shown, it is closely related to Lucilia sericata, the common green fly, and both contribute to sheep strike. Image taken in Australia. Photograph by Lesley Ingram, Bugwood.org.
Selected References
- Anderson GS. 2000. Minimum and maximum development rates of some forensically important Callophoridae (Diptera). Journal of Forensic Science 45: 824-832.
- Apperson CS, Arends JJ, Baker JR, Carter CC, Payne CS. (2011). Blow flies. Insect and Related Pests of Man and Animals. http://ipm.ncsu.edu/ag369/notes/blow_flies.html (30 August 2011).
- Australian Museum. (November 2009). Decomposition: fly life cycle and development times. http://australianmuseum.net.au/Decomposition-fly-life-cycles/ (30 August 2011).
- Baldridge RS, Wallace SG, Kirkpatrick R. 2006. Investigation of nocturnal oviposition by necrophilous flies in central Texas. Journal of Forensic Science. 51: 125-126.
- Byrd JH, Castner JL. 2009. Insects of forensic importance. In Byrd JH, Castner JL (Editors), Forensic Entomology: The Utility of Arthropods in Legal Investigations (2nd Edition). pp. 43-45. CRC Press, Boca Raton, FL. 688 pp.
- Catts EP, Goff ML. 1992. Forensic entomology in criminal investigations. Annual Review of Entomology. 37: 253-272.
- Horobin AJ, Pritchard DI, Shakesheff KM. 2002. How do larvae of Lucilia sericata initiate human wound healing? European Cells and Materials 4 (Supplement 2): 69.
- ITIS. (2011). Phaenicia sericata (Meigen, 1826). Integrated Taxonomic Information System. (30 August 2011).
- Rueda LC, Ortega LG, Segura NA, Acero VM, Bello F. 2010. Lucilia sericata strain from Colombia: Experimental colonization, life tables and evaluation of two artificial diets of the blowfly Lucilia sericata (Meigen) (Diptera: Calliphoridae), Bogota, Colombia strain. Biological Research. 43: 197-203.
- Salimi M, Goodarzi D, Karimfar MH, Edalat H. 2010. Human urogenital myiasis caused by Lucilia sericata (Diptera: Calliphoridae) and Wohlfahrtia magnifica (Diptera: Sarcophagidae) in Markazi Province of Iran. Iranian Journal Arthropod-Borne Disease 4: 72-76.
- Sherman RA, Hall MJR, Thomas S. 2000. Medicinal maggots: an ancient remedy for some contemporary afflictions. Annual Review of Entomology 45: 55-81.
- Strikewise. (2007). Blowfly strike. http://www.strikewise.com/blowfly.html (30 August 2011).
- Tarone AM, Foran DR. 2006. Components of developmental plasticity in a Michigan population of Lucilia sericata (Diptera: Calliphoridae). Journal of Medical Entomology 43: 1023-1033.
- Tarone AM, Foran DR. 2010. Gene expression during blow fly development: Improving the precision of age estimates in forensic entomology. Journal of Forensic Sciences 56: S112-S122.
- Whitworth T. 2006. Keys to the genera and species of blow flies (Diptera: Calliphoridae) of America north of Mexico. Proceedings of the Entomological Society of Washington 108: 689-725.
Authors: Matthew Anderson and Phillip E. Kaufman, University of Florida
Photographs: Joseph Berger; Richard Major, Australian Museum; Susan Ellis; Lesley Ingram; Whitney Crenshaw, Colorado State University
Web Design: Kay Weigel
Publication Number: EENY-502
Publication Date: September 2011.
Copyright University of Florida
An Equal Opportunity Institution
Featured Creatures Editor and Coordinator: Dr. Elena Rhodes, University of Florida
