After death, the human body undergoes decomposition in five stages. A variety of insects may be present for each stage. The fresh stage represents the first few days after death, during which no physical appearance of decomposition is present. The body, however, is actively changing, life functions have ceased and cells and tissues begin to break down. The body cools to the temperature of its surroundings, and insects begin to lay eggs on the body. If the body is on or in the ground, insects native to the soil account for increased insect activity.
The second stage of decomposition is putrefaction, in which the body begins to show more obvious signs of decay, including changes in color and odor, and significant bloating. Chemical processes produce gases which cause facial swelling, as well as gases which fill the abdomen and force fecal matter out of the body. The abdomen turns green from bacterial interaction with hemoglobin. Bacteria enter the veins and interact with the blood, initially causing red streaking; the red streaking later changes to green marbelization of the skin. A greater variety of insects increasingly infest the body. Black putrefaction is the third stage of decomposition, characterized by the darking color of the body, the rupturing of the abdomen, and the escape of abdominal gases following bloating.
This rupture opens the body cavity to a greater variety of insects and scavengers. The black putrefaction stage lasts approximately ten to twenty days, until the bones become visible. The fourth stage is Butyric fermentation, in which the body begins to dry and preserve itself. Odors fade, and the body forms an adipocere, or “grave wax” layer. Organs and tissues reduce and wither. After the organs and tissues are gone, the final stage of decomposition is dry decay, or skeletonization. This is the longest stage, as the chemical structure of bones makes them much slower to deteriorate than soft tissue. The speed of bone decay depends greatly upon the environmental factors present at the body’s location, including moisture, temperature, and especially the pH of the soil.