Nature’s main insect garbage disposers are beetles and flies. Among the beetles, Silphidae are corpse specialists. Members of the genus Nicrophorus are known as burying or sexton beetles because they act as gravediggers, excavating the dirt below a corpse to make a crypt in which their food is protected from cadaver-minded competitors, such as flies. Flies are often the first to find a corpse, so carrion beetles may be faced with competition in the form of fly eggs or larvae, but carrion beetles also have a secret weapon—an entourage of predatory mites that travel on the beetles’ bodies. The strong-flying beetles provide the mites with transportation to the next available dead animal, where they disembark and prey on any fly eggs or larvae already infesting it, thereby reducing the competition to the beetles’ own offspring. Unlike most insects, not only do some male and female burying beetles remain together after mating, they even stick around long enough to care for their young, making little pockets in the corpse to house their offspring and feeding their larvae on well-chewed bits of cadaver. Necrophila, another silphid genus, do not bury their bodies but avoid competition from flies by specializing in cadavers too dry to be a good environment for maggots. Small, colorful, fuzzy-winged beetles in the family Dermestidae, known as skin or carpet beetles, also utilize drier corpses; this preference has made them both highly useful in museums (to convert bodies into clean skeletons) as well as a horrible nuisance (they can turn your painstakingly created insect collection into dust seemingly overnight).
Many flies (Diptera) also utilize corpses for their larvae (maggots), which basically liquefy bodies as they feed. Blow flies and bottle flies (Calliphoridae) are experts at finding fresh corpses on which to lay their eggs, while flesh flies (Sarcophagidae) arrive at the body a bit later but make up for lost time by depositing newly-hatched larvae instead of laying eggs. Some species of coffin fly (Phoridae) can even find and lay eggs in bodies buried six feet under. The rapidity with which carrion flies develop, going from egg to adult in as little as 10 days, once gave rise to the belief that these creatures spontaneously generated from rotting meat. Today, the body of knowledge amassed about the diversity, host preferences, and developmental rates of many cadaver-exploiting flies has made them valuable forensic tools, enabling investigators to determine how long a body has been dead, whether a body was moved after death, and if victims had certain drugs or toxins in their blood when they expired.
Dead bodies need to be broken down, but live animals produce a prodigious quantity of waste that must also be recycled. A staggering 100 billion tons of animals dung are deposited on the earth each day, and once again, insects come to the rescue. Dung beetles, a subgroup of the incredibly diverse scarab family (Scarabaeidae), are perhaps the best-known of these waste recyclers. Politely known as “coprophagous”, these beetles may bury the feces they find, or chew off chunks and roll it away to their burrows. This dung-rolling behavior usually looks a little less stately than its allegorical counterpart of the sun moving across the sky, and the undignified postures of beetles trying to move irregular balls of dung with their hind legs while simultaneously fighting off competitors has also given them the more whimsical name of “tumblebugs”.
Dung beetles are an economically important part of livestock farming; in removing cow pies from the landscape, dung beetles recycle nitrogen into the soil, remove breeding grounds for pests and pathogens, and help keep the forage in pastures palatable to livestock. In the absence of dung beetles, the US cattle industry would have to spend almost $300 million annually to make up for the services these insects provide. Their importance to livestock production is illustrated by the Australian Dung Beetle Project (1966-1986), whose somewhat eyebrow-raising name is belied by the issue’s economic and environmental import. Australia’s marsupials produce understated little pellets of dry fibrous dung, and the beetles that evolved with them are adapted to this type of feces. When big grazing animals such as cattle were brought to Australia by European settlers, their large wet puddles of poop were unpalatable to the native dung beetles, and the country was literally being covered in cow pies. Dr. Gyorgy Ferenc Bornemissza, an entomologist who immigrated to Australia from Hungary, was quick to notice this disgusting landscape feature and suggested bringing in dung beetles from countries with large herbivores. Soon the imported Gazelle Scarab (Orthophagis gazella) was showing its mettle, removing in as little as one day dung pads that would otherwise take years to break down. Bornemissza’s “magnificent obsession” resulted in the release of 43 dung beetle species in Australia, 23 of which established successfully.
Many of the insects that recycle our planet’s waste are in trouble. The American Burying Beetle (Nicrophorus americanus), a handsome black-and-orange jacketed carrion beetle, has been on the Endangered Species List since 1989, when populations were so reduced that its prior U.S. range of 35 states fell to only four. The root of its precipitous decline has never been completely elucidated, though various hypotheses include habitat loss, disease, light pollution, fewer appropriately-sized host animals, or competition for carrion from greater numbers of vertebrate scavengers present due to the removal of large predators. A recent report in Mother Jones detailed the global plight of dung beetles, which are suffering broadly from habitat destruction, decreased dung quantities due to smaller populations of large animals such as rhinos and elephants, and the impacts of anti-worm medications used to treat humans and livestock, much of which ends up deposited in feces. Other types of beetles and flies also rely on carrion or dung, but their status and needs are less well known. Much has been made about the decline of pollinators and the potential impacts on our food system, but it’s time to start thinking too about the less palatable processes that insects mediate so well, and the impacts of human activities on Nature’s insect clean-up crew going quietly about its business beneath our feet.