There are nearly a million known species of insects. Insects are defined by six legs and a body divided into three segments: head, thorax and abdomen. Chitin is an organic material that makes up the exoskeleton of insects. There are three life cycles of insects: ametabolic or incomplete and paurometabolic or gradual, and homotabolic or complete metamorphosis. These life cycles are important in the aging of insects to aid in legal investigations (Houck and Siegel. Entomology). Forensic entomology is the study of insects to aid in legal or criminal investigations. The primary reason to study the presence and life stages of inserts on a decomposing body is to establish the postmortem interval or PMI. Insects can not only be used to determine a PMI, but can also help investigators solve the crime in question. Forensic entomology can be divided into three areas: forensic, urban, and stored product pests. Urban entomology involves insects that affect homes, buildings, and other human environments. Stored pest entomology involves insects infesting stored goods such as food and clothing. In this article, forensic entomology will be the focus because it is the type of entomology that entomologists use to use insects to solve criminal cases (Houck and Siegel. Entomology). Estimation of a PMI: It was found that the decomposition process is best divided into five stages: fresh stage, swollen stage, decomposition stage, post-decomposition stage and remains. The new stage begins at the time of death of the individual and lasts until bloating is observed. The bloating stage usually occurs within two to seven days after death. Putrefaction begins at this stage and the gases produced by the bacteria cause...... middle of paper ......al argument made to prevent the jury from hearing the entomological evidence. It is important to understand the practice of entomology and how it relates to criminal cases. The entomologist must have training in legal practice as well as in his or her scientific discipline (Esf.edu). Conclusion: The main reason to study forensic entomology is to establish the time since death. Recognizing each species and its life stages as well as knowing the length of time an insect is in a particular life stage is the basis for establishing a PMI. The use of forensic entomology is a growing area of ​​research, which will become more prevalent as more research on the subject is conducted. This is important in criminal cases because it allows a time interval to be predicted for when the crime occurred so that it is possible to narrow down the possibility of each suspect or acquit the accused..