Insect succession patterns on pig carrion in southern Nigeria

In analyzing decomposing human remains in cases of unattended death, observing insect succession patterns to aid in estimating the post-mortem interval (PMI) based on carrion insects is one of the tasks of the forensic entomologist. The purpose of this study is to provide baseline data in order to improve PMI estimates using carrion insects. The lingering armed conflict in Nigeria creates a situation where unidentified human remains overwhelm law enforcement agencies. A common challenge is the lack of affordable, easy-to-use, and locally derived methods. This study aims to describe the succession patterns of arthropods, including insects, in pig carcasses in the wet and dry seasons in southern Nigeria as a baseline to aid in PMI estimation. Arthropods were observed and collected (all life cycle stages) in a total of 20 freshly-killed pigs (10 pigs for each season) which were deployed to study sites within 3 h of humane killing and at various times during the two seasons over 14 months. The time of appearance, activity, and disappearance of the arthropods were noted and related to the stages of decomposition to create succession patterns. Three classes, six orders, and 16 families of arthropods were collected. Musca domestica was the first to arrive, followed by Chrysomya marginalis, visiting within 10 min after placement. An ant species (Family Formicidae) had the widest presence through decomposition stages. There was an increase in the absolute number and species richness of arthropods in the wet season. Some arthropods, like the black soldier fly (Hermetia illucens), were exclusively present in the wet season. The observed succession patterns can be used as a reference for forensic scientists to aid in PMI assessment in Nigeria. Arthropods found exclusively in a season could be used to establish the season of death.