It's one thing to have hot dogs on the streets of cities, but there are other types of dead meat in nature that need to be cleaned up. Think of all animals—big and small—that fall where they fall after they die. If they can't be recycled cleanly and neatly, things will become quite unpleasant.
From an insect's point of view, corpses are a fairly convenient source of food – they can't run and won't defend themselves. But insects must move fast, because the carcasses are rich in nutrients, so they become the food that many creatures chase; in addition, there are many species of different sizes involved in this competition.
Here, insects are really fly-weights, and their opponents are heavyweights like foxes, crows, vultures and hyenas. One of the tricks of insect predation is not to lay eggs on the carcass, but to lay hatched larvae, as some members of the sarcophaga genus do. Another trick is to eat fast, grow faster, and be a little more flexible on how long you need to grow before pupating.
Another cunning solution is to hide the body by burying it. The beautiful red and black burial armor from the genus Nicrophorus is the master of this magic. They worked together in pairs to dig up the soil from underneath the corpse and cover it with soil, in such a way that they were able to completely wipe a dead rat from the earth's surface in a single day.
Underground, they clumps the corpses into balls of flesh and lay their own eggs. As jaw-dropping as the choice of parenting locations is, they are still meticulous parents. They bite small pieces of flesh from the corpse and spit back into the mouths of larvae that are not yet capable of digesting food on their own at first. This is one of the few examples of parental care in the insect world other than social insects.
The burial armor also has some good friends who are not insects. As the newly feathered burial shells leave their childhood homes, clusters of tiny mites crawl onto them and hitchhike to the next corpse. The mite only lives in symbiosis with the burial armor: it cannot fly and relies on hitchhiking to find fresh bodies that have just died. In return for a hitchhiking, mites will eat the eggs and larvae of other bugs in the corpse that compete with the burial beetle.
These teams that come to decompose corpses are a rarely mentioned and rarely rewarded corner of the insect world. The bury armor does not have a fan group like bumblebees, but they are extremely important creatures.
In South Asia, people pay a price to learn what happens when scavengers disappear. In fact, the animal we are talking about is the vulture, which can be said to be the big brother of the fly, and enjoys a similar bad reputation among most people. But the essence is the same.
Around the turn of the century, the veterinary drug diclofenac was introduced to India as a treatment for sick cattle. It is hard to imagine that in just 15 years, the drug sent 99% of the vultures in all of India to the west, because the substance would remain on the dead cows and then spread to the vultures that ate them, and the vultures would die of kidney failure.
It is true that scavenger insects are already working at almost full speed, but they still cannot dispose of such a large number of corpses alone. As a result, the dead cattle are left in place. Once the vultures disappear, other large scavengers appear— such as wild dogs— and their numbers proliferate. Since many of them are rabies carriers, the explosion in the number of wild dogs caused by the disappearance of natural ghouls has been the culprit in the 48,000 new rabies deaths in India's population.
Scavengers can also help police conduct criminal investigations because there's a pattern of which species will come to the carcass at what time, and that can be used to help people connect clues in criminal investigations and ultimately solve cases.
It is said that insects first helped identify murderers in 1235, in a small village in China. A man was brutally killed with a sickle, and the local farmers were called up to a meeting. They were instructed to take their own scythes with them. The investigators told them to wait because it was a hot day, and it wouldn't be long before flies would appear. When all the flies landed on the same scythe, its owner was shocked and confessed on the spot. With an unparalleled sense of smell, the flies were drawn to the blood stains, even though the scythe had been washed.
Today, the means of solving crimes are more advanced, but the basic principle is still the same: insect species will appear on corpses in a certain order, following a specific logic. This principle can be used to calculate the time of death, and in some cases it may also reveal some clues about the cause of death.
Drugs and toxins accumulate in insects that appear on site, so they can be easily detected. Such chemicals can also affect the growth rate of maggots that are eating, and thus provide important information for forensic entomologists to estimate the time of death.
In addition, insects are distributed in a certain geographical area. This knowledge can be used to determine whether a corpse has been moved, if the insect species at the site are usually distributed in very different places in the environment, or elsewhere in the country.
In one case, a corpse was found in a sugarcane field in Hawaii, and the oldest larvae found on the corpse belonged to a fly that lived mainly in urban areas. It turned out that the body had been left in an apartment in Honolulu for two days before being discarded in the field.
Insects can also make a more indirect contribution to solving crimes. In the United States, people caught a murderer by falling into insects in the heat dissipation grille of a car. He claimed he was on the East Coast when his family was murdered in California, but the insect species found in his rented car were only found on the West Coast.