It is the time of year when skeletons, skulls and bones have found their way to cookies, porches and windows in the storefront.
While skeletons are universally considered symbols of death, the process of transforming a recently dead animal into a bony skeleton depends on an explosion of life that heralds the process of degradation. Much of this transforming process is performed by twisting, trembling, spinning insects.
Through decades of careful observation and experimentation, entomologists have described a five-step degradation model. This model explains how insects, in close cooperation with microorganisms, transform a warm body into a pile of bones, while at the same time recycling carbon, nitrogen, phosphorus and many other nutrients so that other living things can grow and thrive.
It begins with a corpse
The first stage of decomposition (referred to as “the new stage”
Insects begin to arrive in minutes to hours after the animal dies. Most insects that colonize during this initial period are flies from Calliphoridae (blowflies), Muscidae (houseflies) and Sarcophagidae (meat flies) families.
These early flies are looking for prime real estate to deposit their eggs. This is generally limited to the animal’s natural cavities (eg nostrils or mouth) or within any external damage (eg wear and tear). The moisture levels and soft tissue within these areas make it an ideal nursery habitat for young foods to develop.
Inflation, maggots and methane
Bloat comes then. In this second stage of degradation, oxygen deficiency in the body begins to favor anaerobic microbes. These bacteria thrive in the absence of oxygen in the body.
When the bacteria begin to expel gases such as hydrogen sulfide and methane, the stomach begins to swell. The carcass begins to darken and smells bad. Because carcasses are an uncommon and short-lived source of food, many insects can discover and travel to a carcass miles away.
During the bloating, flying eggs hatch and large numbers of maggots begin to feed on the meat. At this point, beetles participate in the feeding habit. Some beetles, such as meat beetles, will feed on the nutrient-rich meat of the carcass.
Predaceous beetles, such as rove beetles and clown beetles, arrive to feed on the food.
Maggots perform their magic
The third stage is known as “active decay.” This phase begins when the carcass slowly begins to empty, a process similar to a tire punctured by a nail. Larval insects gnaw small holes in the body cavities and allow gases to escape.
Tissue begins to become liquid, giving the carcass a wet appearance followed by the release of a dirty odor. At the end of the active decay step, maggots concentrate their feeding in the chest cavity on the animal. Soon, beetles dominate, with a large, large number of predatory beetles and clown beetles arriving to chow down on the food.
Once most of the meat has been eaten away, the carcass enters the stage of advanced decay. The unpleasant odor of the carcass begins to subside, and most maggots leave the carcass to appear in the underlying soil.
Next, adult beetles arrive at the carcass and begin to lay eggs. Dermestid beetles – small round beetles covered by small scales – are traps that live on various dry materials: fur, feathers, dead plants, even blankets!
If they are not known to you, you may not have looked closely enough – a 2016 study of arthropods in homes discovered dirty beetles in 100 percent of households.
Thus, beetles finish the job
The last stage of decomposition is known as dry decay. Very few adult flies are attracted to the carcass at this time. During dry decay, the carcass is reduced to bone, cartilage, dried skin and hair. At this stage, there is no odor at all.
Larval dermestid beetles continue to clean the skeleton, leaving remnants very similar to a dismantled skeleton. Thus, beetles are so effective at cleansing bones, in fact, that they are regularly used by museums when preparing skeletons for collection and exhibition.
The little things that drive the world
While witnessing this beastly task is not for those with crooked stomachs, the breakdown of animal remains is a fundamental process that cycles nutrients into ecosystems.
Nutrients such as carbon (the basis of all life on earth), phosphorus and nitrogen, which all living things need to grow, are in limited supply in ecosystems. They must be constantly reused and reused to ensure the continuation of life.
After degradation, the soil beneath the carcass will contain a high concentration of nutrients relative to the surrounding ecosystem.
However, the nutrients released into the environment do not all remain in soil and plants. Nutrients and energy contained in the dead animal (whether it is a mouse, a raccoon or a crow) are relocated and repackaged into living, breathing insects.
When these insects move with a carcass, they spread to the wider environment, where they remain productive members of ecosystems.
These very similar insects help pollinate our crops (including pumpkins), fill the stomachs of insectivorous animals (such as bats) and are essential for the decomposition of other dead organisms (such as rats, fungi and snakes).
If you happen to stumble upon animal bones this Halloween season or any other time of the year – take a moment to consider the wild drama that made this discovery possible.
Paul Manning, Postdoctoral Fellow, Faculty of Agriculture, Dalhousie University.
This article is republished from The Conversation under a Creative Commons license. Read the original article.