# Necrophage

Necrophages are organisms that obtain nutrients by consuming decomposing dead animal biomass, such as the muscle and soft tissue of carcasses and corpses (also known as carrion). The term derives from Greek nekros, meaning 'dead', and phagein, meaning 'to eat'. Many hundreds of necrophagous species have been identified including invertebrates in the insect, malacostracan and gastropod classes and vertebrates such as vultures, hyenas, quolls and wolves.
Necrophagous insects are important in forensic science as the presence of some species (e.g. Calliphora vomitoria) in a body, coupled with information on their development stage (e.g. egg, larva, pupa), can yield information on time of death. Information on the insect species present can also be used as evidence that a body has been moved, and analysis of insect tissue can be used as evidence that drugs or other substances were in the body.
Necrophages are useful for other purposes too. In healthcare, green bottle fly larvae are sometimes used to remove necrotic (dead) tissue from non-healing wounds, and in waste management, black soldier fly larvae are used to convert decomposing organic waste into animal feed. Biotechnological applications for necrophage-derived genes, molecules and microbes are also being explored.

## Classification

Necrophages can be classified according to their nutritional reliance on carrion and also their level of adaptation to carrion feeding. Animals are described as 'obligate necrophages' if they use carrion as their sole or main food source and depend on carrion for survival or reproduction. The term 'specialists' is also sometimes used in recognition that these animals have traits favoring necrophagy and making other feeding beahviors difficult. For example, large wingspans facilitate the energy-efficient gliding vultures need to cover long distances in search of carrion, but reduce the agility needed to kill prey. Animals that eat carrion opportunistically and retain the traits needed to find and consume other food sources are described as 'facultative necrophages' and 'generalists'. Both obligate and facultative necrophages are sometimes sub-classified as 'wet' and 'dry' feeders. These terms differentiate animals feeding on moist, putrefying tissue from animals feeding on desiccated and keratinized tissues.

## Invertebrates
### Flies

The European bone skipper, Thyreophora cynophila, is an obligately necrophagous fly. It relies on carrion bone marrow in the first stage of its life cycle. Many other types of fly are facultatively necrophagous. Examples commonly found on land include blow flies, flesh flies, muscid flies, ensign flies and thread-horns. Other necrophagous flies, for example black flies and lake flies, are semi-aquatic. Types of carrion fed upon include wildlife, livestock and poultry carcasses, slaughterhouse and fishing discards, and human bodies. Necrophagous flies detect these dead bodies and body parts via minute traces of decomposition odor in the air.
The diversity and abundance of necrophagous fly species vary geographically and seasonally. For example, Chrysomya species are present in subtropical regions of the USA but are rare in most of Canada. This geographic variation is attributable to factors such as soil type and meteorological conditions, and the effects these have on carrion decomposition. Whether urbanization affects fly species richness is open to dispute. Seasonally, many necrophagous fly species are observed in higher abundance in summer, but Thyreophora cynophila is more active in winter.
Flies play a critical role in forensic science as they are often the first insects to discover and colonize human remains. In cases where a body is submerged, the flies may use the remains as both a food source and attachment site.

### Bees

Vulture bees are a small group of obligately necrophagous bees in the Trigona genus. Trigona worker bees play a similar role to worker bees in the Apis genus; however, along with collecting pollen, nectar, and plant resins, Trigona workers also collect carrion. Although pollen is associated with higher energy value, carrion is preferred by Trigona bees because it is biochemically easier to extract energy from. This dead animal tissue is used as a source of amino acids too.
Cerumen pots are utilized by some Trigona species, such as T. necrophaga, as vesicles to store foodstuff. The foodstuff of T. necrophaga consists of both honey and carrion from vertebrate carcasses. Ultimately, the stored food is utilized by developing larvae and the worker bee itself as a source of nutrition and energy. Due to the rapid decomposition of carrion, especially in warm temperatures, the bees must efficiently metabolize the carrion to avoid rotten carrion in their cerumen pots.
Trigona hypogea communicate the presence of a valuable carcass through olfactory signals. The bees create an odour trail between their nest and the prospective animal carcass; thus, the bees recruit the other nest members to respond and exploit the corpse's resources rapidly. Additionally, interspecific competition is observed in Trigona hypogea bees. The bees are observed to defend their colonized food item, including but not limited to a monkey, lizard, fish, or snake carcass, from competing necrophages, such as flies.

### Beetles

Numerous beetles in the Nicrophorus genus are obligately necrophagous, for example Nicrophorus americanus and N. vespilloides. Many other beetles are facultative necrophages including checkered beetles, dermestid beetles, diving beetles, scarab beetles, silphine beetles and water scavenger beetles. Types of carrion fed upon include wildlife, livestock and poultry carcasses, livestock viscera and human bodies. Necrophagous beetles locate this carrion using antennal chemoreceptors sensitive to sulfur-containing compounds.
N. vespilloides and other burying beetles preferentially feed on small carcasses (e.g. rodents and small birds) as these are easier to transport, clean and conceal from competitors. Diving beetles, scarab beetles and water scavenger beetles have all been observed feeding on amphibian carrion (e.g. granular toads and tree frogs). The scarab beetle Scybalocanthon nigriceps uses its front legs and clypeus to shape frog carrion into pellets for eventual consumption. Other scarab beetles, for example, Coprophanaeus ensifer, build their burrows near carcasses for easier transportation of carrion pieces to offspring.
Beetles that feed on human remains are important in forensic science. Terrestrial beetles such as checkered beetles and dermestid beetles colonize bodies in a predictable sequence and have well-characterized life cycles, so they can sometimes be used to estimate time of death. Aquatic beetles are less useful for estimating time of death but can cause physical damage to submerged bodies that must be distinguished from inflicted injuries when determining cause of death. For example, the facultatively necrophagous diving beetle Rhantus validus creates postmortem channels and chambers in human bodies that must be differentiated from antemortem piercing injuries.

### Marine snails

Nassa mud snails such as Nassarius festivus and Nassarius clarus scavenge on dead and decaying animal matter in the intertidal zone of eulittoral soft shores. At Shark Bay in Australia, Nassarius clarus feeds on the carrion of fishes and bivalves. In the presence of carrion, the animal's proboscis performs a search reaction followed by a quick onset of feeding. When faced with a competitor, such as a hermit crab, at the site of the carrion, the Nassarius clarus attack the competition to defend their meal. Nassarius clarus are attracted to fish and bivalve carrion to a distance of 26 miles and have a heightened interest in areas where the sand has been disturbed; thus, indicating the potential presence of organic detritus or damaged fauna.

## Vertebrates
### Vultures

Necrophagy has been observed in members of the clade Accipitrimorphae, including the Egyptian vulture, Eurasian griffon, cinereous vulture, black vulture, turkey vulture, and the king vulture. The birds, mainly vultures, have been noted to feed on the fleshy tissue and muscle of mammalian vertebrates, such as cows, pigs, and rabbits, as well as other birds. Additionally, the preyed upon carcasses have been recorded to be naturally deceased or the product of anthropogenic events, such as roadkill; thus, the means of prey retrieval may differ depending on spatial circumstances, such as the urbanization of a particular area.
Notably, anthropogenic impacts have had adverse impacts on the biological parameters of necrophagous birds, specifically in the territory of the Azerbaijan Republic. The adverse effects include but are not limited to shortage of food, shootings of birds and nests, and removal of nestlings from nests. Due to the advances of cattle-breeding, involving indoor breeding and the utilization of dead cattle, many necrophagous birds, such as the Eurasian griffon, are losing access to nutritionally valuable cow carcasses. Therefore, the feeding ecology and the interspecific relationships of necrophagous birds are both directly and indirectly impacted by humans.

## Role in forensic entomology

Necrophagous Diptera and Coleoptera play vital roles in the applications of forensic entomology. Necrophagy is critical to forensic scientists because of the production of post-mortem changes on human corpses through myiasis. For example, a forensic medical examiner must determine which soft tissues have been removed as a result of necrophages post-mortem. Entomological data can be utilized in homicide cases to determine the post-mortem interval (PMI) and localize the crime. This information is indicated by the time it takes the necrophage larvae to reach a particular developmental stage; thus, the life cycle of the necrophage provides detail regarding the interval between the initial myiasis and the discovery of the corpse. Notably, the colonization of a human corpse by Diptera necrophages is positively correlated with particular injuries, such as gunshot wounds and lacerations. The nature of these injuries provides higher levels of accessibility for the necrophagous Diptera and allows them to colonize the corpse rapidly.
Seasonal changes, particularly temperature changes, significantly affect the abundance and degree of myiasis of necrophages. The increase or decrease in temperature that accompanies seasonal changes determines the rate of development retained by necrophages, particularly Diptera. High temperatures lead to an exponential increase in the rate of development in Diptera. Therefore, the body temperature of a corpse is of utmost importance to necrophages, as they prefer fresh internal tissue and sexually thrive in warm environments. However, the corpse's temperature may have adverse effects on the determination of the post-mortem interval (PMI) because the necrophages' development may be rapid due to body's temperature and not the passage of time.
In addition, Coleoptera provide valuable information to forensic entomologists. Specifically, in the later stages of decomposition, Dermestidae and Cleridae have been recorded to colonize human corpses and provide insight regarding the post-mortem interval (PMI). However, researchers note that there are spatial differences that affect the latency of necrophagous Coleoptera presence.