The common green bottle fly, Lucilia sericata, is a ubiquitous insect species with a significant impact on various fields, ranging from forensic science to medicine. This article delves into the intricate details of its diet, life cycle, and broader ecological and economic implications.
Appearance and Identification
Bottle flies are easily recognized by their striking colors and unique features. Their colors can vary widely-from shimmering metallic blues and greens to deep blacks. This color variation not only makes them eye-catching but also helps with temperature control and protection from predators. For instance, about 30% of bottle flies have a bright blue or green hue, allowing them to blend into their surroundings more effectively.
Adult Common Green Bottle Flies are a metallic green color, with some having shades of yellow on their shiny bodies. All have black hairs sparsely covering the body and large red eyes. The adults are usually a metallic green and can also have a copper green color. The mouthparts are usually yellow. The back is hairy, and the overall diameter is about 8-10 mm (~1/3 in). The squamae at the base of the wings are hairless.
In terms of size, these flies typically measure between 6 to 14 millimeters in length. Its body is 10-14 mm (0.39-0.55 in) in length - slightly larger than a house fly - and has brilliant, metallic, blue-green or golden coloration with black markings. They have robust bodies with hairy surfaces and large, compound eyes, making them a familiar sight across different habitats.
The defining characteristic of L. sericata and the one most used when identifying the adult fly is the presence of three bristles on the dorsal mesothorax, located on the middle of the back of the fly. L. sericata is almost identical to its conspecific, L. cuprina, and identification between them requires microscopic examination of two main distinguishing characteristics. L. sericata is blue-black, as opposed to L. cuprina, which has a metallic green femoral joint in the first pair of legs. Also, when looking at the occipital setae, L. sericata has one to nine bristles on each side, while L. cuprina has three or less. Additionally, the eyes of L. sericata are smaller, with the frontal stripe also being thinner than the ones of the L.
Read also: The Diet of the Common Warthog
Distribution
Lucilia sericata is found throughout the world but is more specifically described as having a Holarctic (Northern Hemisphere) distribution, being widely distributed throughout the United States and southern Canada. Despite being mostly Holarctic, Lucilia sericata is now found commonly in Australia and in several South and Central American countries.
Lucilia sericata is common all over the temperate and tropical regions of the planet, including Europe, Africa, and Australia. It prefers warm and moist climates, so is especially common in coastal regions, but can also be found in arid areas.
The territorial heat map showcases the states and territories of North America where the Common Green Bottle Fly may be found (but is not limited to). This sort of data is useful when attempting to see concentrations of particular species across the continent as well as revealing possible migratory patterns over a species' given lifespan. Some insects are naturally confined by environment, weather, mating habits, food resources and the like while others see widespread expansion across most, or all, of North America. States/Territories shown above are a general indicator of areas inhabited by the Common Green Bottle Fly.
Life Cycle and Reproduction
Understanding the life cycle of bottle flies offers insights into their critical ecological role. Bottle flies undergo complete metamorphosis, consisting of four stages: egg, larva (maggot), pupa, and adult. The female lays around 100 to 200 eggs on decaying material like garbage or animal remains, providing a nutrient-dense environment for the larvae.
The eggs of Lucilia sericata are usually white but can be a pale yellow. They are often deposited in batches or masses. The eggs are elongated with one end tapered slightly and are approximately 1.5 mm (< 1/16 in) long. At approximately 21°C (69.8°F), Lucilia sericata eggs take about 21 hours to hatch, and at 27°C (80.6°F) it takes about 18 hours to hatch, following their deposition. The female lays her eggs in carrion of all kinds, sometimes in the skin or hair of live animals, causing myiasis.
Read also: Omnivorous Starling
After hatching, the larvae begin to consume the decomposing material. This feeding accelerates decomposition and recycles valuable nutrients back into the ecosystem. Research indicates that the presence of bottle fly larvae can increase the breakdown of organic waste by up to 15%, significantly aiding in waste management.
All stages of the larvae are smooth. They are conical-shaped and have a complete peritreme (area surrounding the spiracles) on their posterior spiracles (structures, which look similar to eyes, on the rear of the larvae that are used for respiration). The larvae are white or yellowish through all three instars of development and reach a maximum of 12-18 mm (1/2-¾ in) before pupation. Larval development requires approximately four days at 20°C (68°F) and three days at 27°C (80.6°F). There are three instars through which the larvae develop. However, many other factors play a role in development, including the food source and humidity.
Once fully developed, the 3rd instar larvae leave the host or carrion and burrow into the soil or substrate surrounding it. Pupal development takes approximately 10 days at 21°C (69.8°F) and seven days at 27°C (80.6°F), after which the adult fly emerges. The pupae are enclosed in a hardened shell that is usually reddish brown, light brown or black in color. This shell is comprised of the last larval instar skin. They are 9-10 mm (~1/3 in) long with a width ranging from 3 to 4 mm (1/8 in).
After mating, adult females lay clusters of up to 200 eggs at a time, on the host or carcass. Adults usually lay eggs about 2 weeks after they emerge. Their complete lifecycle typically ranges from 2 to 3 weeks, but this varies with seasonal and other environmental circumstances. L. sericata usually completes three or four generations each year in cold, temperate climates, and more in warmer regions.
After several days of feeding, the larvae migrate away from the food source to find a dry place to pupate. This pupal stage can last from a few days to several weeks, after which the adult flies emerge, continuing the cycle.
Read also: Feeding Your Degu
Feeding Habits and Diet
The feeding habits of bottle flies are diverse and adapted to their developmental stages.
As adults, bottle flies primarily feed on liquids such as nectar and sugary substances, which not only provides energy but also aids in pollination. Adult Common Green Bottle Flies drink nectar and help pollinate crops like broccoli, cabbage, collard greens, onions, and kale. Estimates suggest that adult bottle flies can contribute to pollination for nearly 20% of flowering plants, showcasing their ecological importance beyond decomposition.
The adults are more varied in their diets, eating carrion and feces, as well as pollen and nectar, as they are important pollinators in their native range and important agents of decomposition. The pollen (which the flies can digest, perhaps with the assistance of bacteria in their digestive tracts) may be used as an alternative protein source, especially for gravid females who need large amounts of protein and cannot reliably find carrion. Notably, gravid flies are particularly attracted to sapromyophilous flowers that exude a carrion-like odor, such as the dead horse arum lily. These flowers are tricking the flies into pollinating them by mimicking the scent of a corpse, but the flies also frequently visit myophilous flowers such as the oxeye daisy, and are attracted to the color yellow, as well as to the scent of flowers.
Conversely, the larvae, or maggots, have a scavenging diet. Common Green Bottle Fly larvae eat from the carcasses of dead animals. They thrive on decomposing organic material, playing a crucial part in breaking down waste. The larvae of L. sericata feed exclusively on dead organic tissue; as the eggs are laid directly into carrion, they are able to feed on the corpse on which they hatch until they are ready to pupate. This scavenging behavior helps control waste buildup, further highlighting the ecological significance of bottle flies.
Habitat and Ecological Role
The habitat of bottle flies is closely linked to their feeding habits and life cycle.These flies thrive in areas rich in decaying organic material. Common habitats include animal carcasses, compost piles, and areas with human waste. Their association with decomposition allows them to flourish where many other insects might find it challenging to survive.
In their natural environment, bottle flies play an important role in the ecosystem. By breaking down dead matter, they facilitate nutrient cycling and contribute significantly to soil health. Without them, ecosystems would struggle with slower decomposition processes, leading to excess organic waste.
Medical and Forensic Significance
The significance of bottle flies goes beyond their ecological contributions; they are also important in medical and forensic contexts.
Forensic Entomology
Lucilia sericata is very important in the field of forensic science. The timing of this species' life cycle is well-studied and useful information thanks to its diet and habitat. The immature flies are used to estimate the minimum portion of the post-mortem interval, known as PMI, in a multitude of settings. According to The Australian Museum (2009), Lucilia sericata is one of the first insects to arrive at a corpse. Byrd and Castner (2009) go further and state that calliphorids have appeared on carcasses in experiments within minutes of death. They also state that calliphorids, along with scarophagids (flesh flies) and muscids (filth flies) are the most important species in providing accurate PMI estimations.
In forensic entomology, the presence of bottle flies on a corpse can provide clues about the time of death. Experts can estimate how long a body has been deceased based on the development stage of the flies. Knowing the size and life stage of the maggots makes their presence at a crime scene useful in timing the decomposition of corpses. This species of adults is one of the first flies to arrive on a corpse. Thanks to short lives, they move through various life stages in days, not weeks or years, offering valuable information to forensic teams. For example, if bottle fly larvae are 5 days old, investigators can estimate the time of death within a narrow window around that timeframe.
The most common way of estimating PMI using dipteran larvae, such as Lucilia sericata, is to determine the developmental stage the immature is in when collected. Although this method is usually accurate, it can vary, as many factors can determine the growth rate of a larva.
Lucilia sericata also has been shown to oviposit in cool nocturnal conditions, which are quite uncharacteristic to the normal daytime ovipositing behavior of it and other calliphorids (Catts and Goff 1992). This behavior is uncommon and there is a short period of time after sunset that necrophilous flies will oviposit, and it is thought to be dependent on the local presence of flies near a corpse and the availability of artificial lights illuminating the area.
Maggot Therapy
Lucilia sericata is a commonly used species in human wound treatment for injuries that conventional treatments fail to heal. This practice is called maggot therapy, and its use continues to increase. Maggots have also been used medicinally to clear rotting tissue from humans when surgical options are ineffective or impossible.
Under the guidance of a physician, Lucilia sericata larvae are placed on a wound, the wound is then wrapped and the larvae feed on the necrotic (dead) tissue and bacteria that occur in an infected wound. Their activity in a wound increases the promotion of healthy tissue growth. This is achieved by not only eating the decomposing tissue but also secreting and producing antimicrobial enzymes while in the wound. When placed in an infected, necrotic area, the maggots carefully devour the dead tissue, sparing the healthy tissue, thereby cleaning the wound. Most patients receiving maggot therapy treatment have no pain. Initially, contamination of wounds was a concern, but proper use of sterile maggots has eliminated any chance of maggot-transmitted microorganisms.
Health Risks
However, bottle flies can also pose health risks. They may carry harmful bacteria and viruses, making them a concern in medical and veterinary settings. Numerous flies congregate on filthy materials, like garbage, feces and rotting food, for feeding and reproductive purposes. Flies lay eggs in decaying organic materials in order to provide developing larvae with a nourishing environment upon hatching. Eating food containing blow fly eggs and larvae will cause serious gastric and enteric illness, such as E. coli, rotavirus and shigella.
Effective management strategies are necessary to minimize their potential health impacts, particularly in high-risk areas.
Economic Importance and Pest Management
While bottle flies have beneficial ecological roles, they can also be seen as pests.
Agricultural Impact
This same species, however, is detrimental to sheep. Lucilia sericata and a similar species, Lucilia cuprina (Wiedemann), are known in Britain and Australia for causing sheep strike. As a result, Lucilia sericata is sometimes called the sheep blow fly. Sheep strike, also known as blowfly strike, is a type of myiasis (invasion of living tissue by fly larvae) and usually is observed near the rear of the sheep where there is fecal matter and urine on the wool. The fly favours host species of the genus Ovis, domestic sheep in particular, and sometimes lays eggs in the wet wool of living sheep. This can lead to blowfly strike, causing problems for sheep farmers.
Nuisance Pests
These flies are often attracted to garbage and waste, becoming common nuisances, especially during warm weather. Several species of blow flies are common pests throughout the US, and their habit of congregating onto pathogen rich decaying materials, most notably animal carcasses, makes the pests capable of spreading diseases to humans. Several blow fly species are known for infesting homes, especially homes located near slaughterhouses, meat processing plants and landfills. Two groups of blow fly pests, greenbottle and bluebottle flies, freely invade homes regularly no matter the location, as they are able to disperse over unusually long distances compared to other fly pests.
Their presence can prompt homeowners to take measures to deter them, emphasizing the importance of waste management and sanitation practices. For instance, adopting proper garbage disposal methods can reduce fly attraction by nearly 40%.
Pest Control Strategies
Recognizing the signs of a bottle fly infestation is the first critical step in pest control. Common indicators include:
- Adult Flies: You may notice them buzzing around food or waste areas.
- Clusters of Eggs: Typically found in moist, decaying matter.
- Foul Odors: This often indicates a breeding site nearby.
Locating Breeding Sources is essential for an effective pest management plan. The importance of inspecting various areas, including:
- Garbage Disposal Units: Food remnants can be a breeding ground.
- Open Trash Bins: Unsecured waste can attract flies.
- Pet Waste in Yards: Organic waste is a prime target for flies.
- Compromised Compost Piles: Decomposing matter, if not managed properly, can attract these pests.
Once breeding sites are located and cleaned, immediate control methods can eliminate existing adult flies, such as:
- Insect Growth Regulators (IGRs): By disrupting the flies' development, these substances prevent larvae from becoming adults, significantly reducing future populations.
- Liquid Treatments: Targeted pesticide applications can kill adult flies upon contact, providing fast relief.
- Traps and Baits: These devices help capture flies, reducing numbers while longer-term treatments take effect.
Sustaining a fly-free environment requires proactive measures like:
- Maintain Cleanliness: Dispose of food waste properly and seal trash bins to minimize attractants.
- Regular Inspections: Conduct routine checks of your home and yard to catch problems early, sometimes identifying trouble before infestations can become severe.