Megaselia scalaris
Encyclopedia
The fly
Megaselia scalaris is a member of the order Diptera
and the family Phoridae. The family members are commonly known as the "humpbacked fly", the "coffin fly", and the "scuttle fly". The name "scuttle fly" derives from the jerky, short bursts of running, characteristic to the adult fly. The name "coffin fly" is due to that fact that they are found in coffin
s, digging six feet deep in order to reach buried carrion. It is one of the more common species
found within the family Phoridae; more than 370 species have been identified within North America.
in 1866.
are sometimes enlarged or distinctively shaped, especially in females. The antennae are sometimes hidden by first flagellomere.
The thorax
is large and frequently described as having a “humpbacked structure.” Major bristle
s of body are characteristically feathered in this region; this is a characteristic unique to M. scalaris. Legs are attached to the thorax. They are usually well developed with a stout, enlarged, laterally compressed hind femur
. A variety of sensory organs are present on the posterior surface. The tibia
is frequently composed of short, closely set setae. The wings are also attached to the thoracic region. M. scalaris’ wings are usually large and fringed with short to long setae. Several tiny pore-like sensory organs, not associated with bristles or setae, are present at various places on the anterior veins. The distributional pattern is generally evident.
The abdomen
is the third body region. It is well developed with typically three to six tergites and seven spiracle
s present.
, larva
, pupa
, and adult. There are three distinct larval instar
s of M. scalaris. The third instar of development usually lasts longer than the first two because there are dramatic changes from a larva into a fly. The development of each life cycle depends on the environmental conditions in which the larva are feeding or being reared. It generally occurs “at 22-24°C, the first instar lasts 1-2 days, the second 1-2 days, and the third 3-4 days before pupation and a further 1-2 days before pupation." The larvae are usually very small, roughly 10mm in length. Twelve distinct segments are usually visible on the larvae.
source; however, Megaselia scalaris is an omnivorous species. It has been recorded feeding on plants, wounds, and corpses. Protein
food sources are preferred by the females preceding maturation of their eggs. All meals must be a fluid in order for the flies to access the meal because Megaselia scalaris has sponging mouthparts
. This is a characteristic common to the family Phoridae.
Both male and female species have five pairs of sharp teeth. These are not used in retrieval of a food source, like a piercing mouthpart, but are instead used to aid digestion and breakdown of nutrients. Human cases involving skin inflammation
are likely due to these teeth. It is important to note the distinction that while Megaselia scalaris can feed on blood meals, the teeth are not used to puncture the host. The blood must be found on the body as an exudate
. One theory to the evolution of these teeth is that Megaselia scalaris uses them in order to exit their pupal casings.
because evidence derived from the lifecycle and behavior of these flies is useful in both medicocriminal and abuse/neglect cases and is admissible in court.
Megaselia scalaris are small in size; this allows them to locate carrion
buried within the ground and to locate bodies concealed in coffins. They can travel 0.5 m in a four day period. They lay their eggs on carrion to provide food for the hatched larvae.
Often, Megaselia scalaris may be the only forensic entomological evidence available if the carrion is obstructed or concealed in a place that is hard for other insects to reach. Larger flies are not always able to reach the carrion. Calculations involving "M. scalaris" can result in an insect colonization time that can be used for a postmortem interval, which may help establish an estimated time of death. M. scalaris are classified in a secondary forensic role because they prefer older decaying carrion.
Evidence collected by forensic entomologists involving Megaselia scalaris has been used to demonstrate in court that caretakers have neglected the care of their elderly patients. Megaselia scalaris is also involved in cases of myiasis
. Megaselia scalaris larvae found on a body can be used in court as a tool to show “time of death” or “time of neglect.”
, developmental, and bioassay
studies. Research has also been done on the unique neurophysiology
and neuromuscular junction within this fly, giving it its characteristic "scuttle" movement. In comparison to Drosophila melanogaster, M. scalaris has decreased excitatory postsynaptic potentials (EPSPs) and facilitation of EPSPs in response to repetitive stimulation. With such a wide range of food sources, the larvae can be considered facultative predators, parasitoid
s, or parasites.
behavior. Because the M. scalaris is omnivorous, its sponge mouthparts
allow it to feed on fluid from plants, wounds and corpses. The larva
e feed on a more extensive range of decaying organic materials than any other fly species. Its ability to thrive in unsanitary conditions, and its ability to feed on decaying material, enables authorities to establish a time of death or to determine neglect or can be used as evidence in court cases.
Fly
True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...
Megaselia scalaris is a member of the order Diptera
Fly
True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...
and the family Phoridae. The family members are commonly known as the "humpbacked fly", the "coffin fly", and the "scuttle fly". The name "scuttle fly" derives from the jerky, short bursts of running, characteristic to the adult fly. The name "coffin fly" is due to that fact that they are found in coffin
Coffin
A coffin is a funerary box used in the display and containment of dead people – either for burial or cremation.Contemporary North American English makes a distinction between "coffin", which is generally understood to denote a funerary box having six sides in plan view, and "casket", which...
s, digging six feet deep in order to reach buried carrion. It is one of the more common species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
found within the family Phoridae; more than 370 species have been identified within North America.
Taxonomy
Megaselia scalaris was described by the German entolomogist Hermann LoewHermann Loew
Friedrich Hermann Loew was a German entomologist who specialised in the study of Diptera, an order of insects including flies, mosquitoes, gnats and midges...
in 1866.
Description
Much of the anatomy of this fly is common to the family Phoridae. Megaselia scalaris flies are blackish, brownish, yellowish minute flies with a small, rather flattened head. Ommatrichia or hair-like processes, are located between the facets of the compound eye. The lower facial margin and clypeusClypeus
The clypeus is one of the sclerites that makes up the "face" of an arthropod.In insects, the clypeus delimits the lower margin of the face, with the labrum articulated along the ventral margin of the clypeus. The mandibles bracket the labrum, but do not touch the clypeus. The dorsal margin of the...
are sometimes enlarged or distinctively shaped, especially in females. The antennae are sometimes hidden by first flagellomere.
The thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
is large and frequently described as having a “humpbacked structure.” Major bristle
Bristle
A bristle is a stiff hair or feather. Also used are synthetic materials such as nylon in items such as brooms and sweepers. Bristles are often used to make brushes for cleaning uses, as they are strongly abrasive; common examples include the toothbrush and toilet brush...
s of body are characteristically feathered in this region; this is a characteristic unique to M. scalaris. Legs are attached to the thorax. They are usually well developed with a stout, enlarged, laterally compressed hind femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
. A variety of sensory organs are present on the posterior surface. The tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
is frequently composed of short, closely set setae. The wings are also attached to the thoracic region. M. scalaris’ wings are usually large and fringed with short to long setae. Several tiny pore-like sensory organs, not associated with bristles or setae, are present at various places on the anterior veins. The distributional pattern is generally evident.
The abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
is the third body region. It is well developed with typically three to six tergites and seven spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s present.
Egg and larva
The development of Megaselia scalaris fly is holometabolous, consisting of four distinct stages. These stages include: eggEgg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
, larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
, pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
, and adult. There are three distinct larval instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
s of M. scalaris. The third instar of development usually lasts longer than the first two because there are dramatic changes from a larva into a fly. The development of each life cycle depends on the environmental conditions in which the larva are feeding or being reared. It generally occurs “at 22-24°C, the first instar lasts 1-2 days, the second 1-2 days, and the third 3-4 days before pupation and a further 1-2 days before pupation." The larvae are usually very small, roughly 10mm in length. Twelve distinct segments are usually visible on the larvae.
Pupa and adult
The male Megaselia scalaris fly matures more quickly than the female pupa, emerging two days prior to the females. Emerging before the females gives the males the advantage to feed allowing their sperm to mature and be ready by the time the females emerge. Adult Megaselia scalaris reproduce by means of oviposition. The females lay relatively large eggs for their size due to the extended incubation period of the eggs.Feeding habits
Many of the flies within the family Phoridae prefer nectar as an energyEnergy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
source; however, Megaselia scalaris is an omnivorous species. It has been recorded feeding on plants, wounds, and corpses. Protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
food sources are preferred by the females preceding maturation of their eggs. All meals must be a fluid in order for the flies to access the meal because Megaselia scalaris has sponging mouthparts
Insect mouthparts
Insects exhibit a range of mouthparts, adapted to particular modes of feeding. The earliest insects had chewing mouthparts...
. This is a characteristic common to the family Phoridae.
Both male and female species have five pairs of sharp teeth. These are not used in retrieval of a food source, like a piercing mouthpart, but are instead used to aid digestion and breakdown of nutrients. Human cases involving skin inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
are likely due to these teeth. It is important to note the distinction that while Megaselia scalaris can feed on blood meals, the teeth are not used to puncture the host. The blood must be found on the body as an exudate
Exudate
An exudate is any fluid that filters from the circulatory system into lesions or areas of inflammation. It can apply to plants as well as animals. Its composition varies but generally includes water and the dissolved solutes of the main circulatory fluid such as sap or blood...
. One theory to the evolution of these teeth is that Megaselia scalaris uses them in order to exit their pupal casings.
Habitat
Megaselia scalaris’ optimal culture temperature is 28 degrees Celsius. They are common in many areas but thrive predominately in moist unsanitary vicinities such as dumpsters, trash containers, rotting meat, vegetable remains, public washrooms, homes, and sewer pipes. Although referred to as scavengers, adults are known to feed primarily on sugars. The larvae, however, depend on moist decaying plant or animal material and feed on a wide range of additional decaying material. “The larvae display a unique behavior of swallowing air when exposed to pools of liquid. This intake of air allows them to float, and may prevent drowning during flood conditions in their normal habitat.”Importance to forensic entomology
Megaselia scalaris are important in the study of forensic entomologyForensic entomology
Forensic entomology is the application and study of insect and other arthropod biology to criminal matters. It is primarily associated with death investigations; however, it may also be used to detect drugs and poisons, determine the location of an incident, and find the presence and time of the...
because evidence derived from the lifecycle and behavior of these flies is useful in both medicocriminal and abuse/neglect cases and is admissible in court.
Megaselia scalaris are small in size; this allows them to locate carrion
Carrion
Carrion refers to the carcass of a dead animal. Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters include vultures, hawks, eagles, hyenas, Virginia Opossum, Tasmanian Devils, coyotes, Komodo dragons, and burying beetles...
buried within the ground and to locate bodies concealed in coffins. They can travel 0.5 m in a four day period. They lay their eggs on carrion to provide food for the hatched larvae.
Often, Megaselia scalaris may be the only forensic entomological evidence available if the carrion is obstructed or concealed in a place that is hard for other insects to reach. Larger flies are not always able to reach the carrion. Calculations involving "M. scalaris" can result in an insect colonization time that can be used for a postmortem interval, which may help establish an estimated time of death. M. scalaris are classified in a secondary forensic role because they prefer older decaying carrion.
Evidence collected by forensic entomologists involving Megaselia scalaris has been used to demonstrate in court that caretakers have neglected the care of their elderly patients. Megaselia scalaris is also involved in cases of myiasis
Myiasis
Myiasis is a general term for infection by parasitic fly larvae feeding on the host's necrotic or living tissue. Colloquialisms for myiasis include flystrike, blowfly strike, and fly-blown. In Greek, "myia" means fly....
. Megaselia scalaris larvae found on a body can be used in court as a tool to show “time of death” or “time of neglect.”
Current and future research
Megaselia scalaris is commonly used in research and within the lab because it is easily cultured; this species is used in experiments involving geneticGenetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
, developmental, and bioassay
Bioassay
Bioassay , or biological standardization is a type of scientific experiment. Bioassays are typically conducted to measure the effects of a substance on a living organism and are essential in the development of new drugs and in monitoring environmental pollutants...
studies. Research has also been done on the unique neurophysiology
Neurophysiology
Neurophysiology is a part of physiology. Neurophysiology is the study of nervous system function...
and neuromuscular junction within this fly, giving it its characteristic "scuttle" movement. In comparison to Drosophila melanogaster, M. scalaris has decreased excitatory postsynaptic potentials (EPSPs) and facilitation of EPSPs in response to repetitive stimulation. With such a wide range of food sources, the larvae can be considered facultative predators, parasitoid
Parasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
s, or parasites.
Conclusion
The study of Megaselia scalaris is forensically important in the field of urban and medicocriminal entomology due to the species’ unique physical characteristics and locomotiveAnimal locomotion
Animal locomotion, which is the act of self-propulsion by an animal, has many manifestations, including running, swimming, jumping and flying. Animals move for a variety of reasons, such as to find food, a mate, or a suitable microhabitat, and to escape predators...
behavior. Because the M. scalaris is omnivorous, its sponge mouthparts
Mouthparts
The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style or mode of feeding. Most mouthparts represent modified, paired appendages, which in ancestral forms would have appeared more like legs than mouthparts. In general, arthropods have mouthparts for...
allow it to feed on fluid from plants, wounds and corpses. The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e feed on a more extensive range of decaying organic materials than any other fly species. Its ability to thrive in unsanitary conditions, and its ability to feed on decaying material, enables authorities to establish a time of death or to determine neglect or can be used as evidence in court cases.