Decomposition refers to the reduction of the body of a formerly living organism into simpler forms of matter. The body of a living organism begins to decompose shortly after death. Such decomposition can be simplified in two stages: In the first stage, it is limited to the production of vapors. In the second stage, liquid materials form and the flesh or plant matter begins to decompose.

There are environmental influences that will affect decomposition. A body that is exposed to air will decompose more quickly and will have more insect activity. A buried body will decompose eight times slower than a body exposed to air. This is due in part to limited insect activity and possibly lower temperatures. Likewise a body submerged in water decomposes at half the rate of an exposed body. The rate of decomposition depends on the temperature of the water. Cold water will allow slow decomposition and warm water causes faster decomposition. The body is also shielded from insect activity as long as it is submerged.

Once death occurs, human decomposition takes place in stages. The process of tissue breakdown may take from several days to years.

Stages

Fresh

The fresh stage of decomposition occurs during the first few days following death. There are no physical signs of decomposition during this time. However, homeostasis of the body has ceased to function which allows cellular and soft tissue changes to occur because of the process of autolysis, the destruction of cells and organs due to an aseptic chemical process. At this point, the body enters algor mortis, the cooling of the body’s temperature to that of its surroundings. When the body’s cells reach the final stage of autolysis, an anaerobic environment is created. This allows the body’s normal bacteria to breakdown the remaining carbohydrates, proteins, and lipids. The products from the breakdown create acids, gases, and other products which cause volatile organic compounds (VOCs), and putrefactive effects. According to Science Direct, VOCs are produced during the early stage of human decomposition.

Putrefaction

Odor, color changes, and bloating of the body during decomposition are the results of putrefaction. The lower part of the abdomen turns green due to bacteria activity in the cecum. Bacteria break down hemoglobin into sulfohemoglobin which causes the green color change. A formation of gases enters the abdomen which forces liquids and feces out of the body. The gases also enter the neck and face, causing swelling of the mouth, lips, and tongue. Due to this swelling and disconfiguration of the face, identification of the body can be difficult. Bacteria also enter the venous system causing blood to hemolyze. This leads to the formation of red streaks along the veins. This color soon changes to green, through a process known as marbelization. It can be seen on the shoulders, chest and shoulder area, and thighs. The skin can blister and have a serous fluid inside. The skin also becomes fragile, leading to skin slippage, making it difficult to move a body. Body hair comes off easily. The color change of the discoloration from green to brown marks the transition of the early stage of putrefaction to the advanced decompositional stages.

Black putrefaction

After the body goes through the bloating stage it begins the black putrefaction stage. At this point the body cavity ruptures, all of the abdominal gases begin to escape and the body darkens from its greenish color. These activities allow for a greater invasion of scavengers, and insect activity increases greatly. This stage ends as the bones become apparent, which can take anywhere from 10 to 20 days after death depending on region and temperature. This period is also dependent on the degree to which the body is exposed.

Butyric fermentation

After the early putrefaction and black putrefaction phases have taken place, the body begins mummification, in which the body begins to dry out. The human carcass is first mummified, and then goes through adipocere formation. Adipocere (grave wax) formation refers to the loss of body odor and the formation of a cheesy appearance on the cadaver. Mummification is considered a post-active stage because there is less definite distention between changes and they are indicated by reduced skin, cartilage, and bone. Mummification is also indicated when all of the internal organs are lost due to insect activity.

Dry decay

When the last of the soft-tissue has been removed from the body, the final stage of decomposition, skeletonization, occurs. This stage encompasses the deterioration of skeletal remains, and is the longest of the decomposition processes. Skeletonization differs markedly from the previous stages, not only in length, but in the deterioration process itself.

The strength and durability of bone stems from the unique protein-mineral bond present in skeletal formation; consequently, changes to skeletal remains, known as bone diagenesis, occur at a substantially slower rate than stages of soft-tissue breakdown. As the protein-mineral bond weakens after death, however, the organic protein begins to leach away, leaving behind only the mineral composition. Unlike soft-tissue decomposition, which is influenced mainly by temperature and oxygen levels, the process of bone breakdown is more highly dependent on soil type and pH, along with presence of groundwater. However, temperature can be a contributing factor, as higher temperature leads the protein in bones to break down more rapidly. If buried, remains decay faster in acidic-based soils rather than alkaline. Bones left in areas of high moisture content also decay at a faster rate. The water leaches out skeletal minerals, which corrodes the bone, and leads to bone disintegration.

Insect activity

Substances produced during the fresh stage attract a variety of insects. Many of the Diptera insects begin to lay their eggs on the body during this stage, especially the Calliphoridae. There is also considerable insect activity by the insects that live in the soil around the body.

During putrefaction the majority of the insects begins with the Calliphoridae, and include Formicidae, Muscidae, Sphaeroceridae, Silphidae, Lepidoptera, Hymenoptera, Sarcophagidae, Histeridae, Staphylinidae, Phalangida, Piophilidae, Aranae, Sepsidae, and Phoridae. Again, there is also considerable insect activity by the soil-inhabiting arthropods.

There is considerable insect activity during black putrefaction. Some of the insects that can be found living in the body are the Calliphoridae larvae, Staphylinidae, Histeridae, Gamasid mites, Ptomaphila, Trichopterygidae, Piophilid larvae, Parasitic wasps, Staphylinid larvae, Trichopterygid larvae, Histerid larvae, Ptomaphila larvae, Dermestes, Tyroglyphid mites, Tineid larvae, and the Dermestes larvae. Some insects can also be found living in the soil around the body such as Isopoda, Collembola, Dermaptera, Formicidae, Pseudoscorpiones, Araneae, Plectochetos, Acari, Pauropoda, Symphyla, Geophilidae, and Protura. Finding these insects is what was found on a body in Australia. The types of insects will differ based on where the body is, although Diptera larvae can be found feeding on the body in almost all cases.

Insects that can be found on the body during mummification include most of the same insects as in putrefaction stage, but also include Acarina, Nitidulidae, Cleridae, Dermestes caninus, and Trogidae. The main soil-inhabiting arthropods include Dermaptera and Formicidae.

At the dry decay stage commonly found insects include Sphaeroceridae, Acarina, Nitidulidae, Cleridae, Dermestes caninus, Trogidae, Tyroglyphid mites, and the Tineid larvae. The soil-inhabiting arthropods are Collembola, Dermaptera, Heteroptera, Coleoptera and their larvae, parasitic Hymenoptera, Formicidae, Diptera larvae, Psuedoscorpiones, Aranae, Plectochetos, Acari, Pauropoda, Symphyla, Geophilidae, Protura, and Aphididae.