Forensic entomology: crime solving insects
UDEA/DICYT “Insects are fascinating,” says Professor Martha Wolf, an entomologist at the University of Antioquia who has long been devoted to study the role of insects in death investigations, and current director of the UA Entomology Group (GEUA), established in 1997.
The use of insects in forensic investigations dates back to the 13th century in China as evidenced by Chinese physician and forensic expert Song Ci (also known as Sung T’zu) in his book “The washing away of wrongs”.
The UA Entomology Group has compiled a vast collection of insect species that are used to estimate the time elapsed since death or post mortem interval (PMI), and determine whether a body has been moved from its original place of death.
Professor Wolf recalls the case of two women accused of murdering a young man after the body was found inside an apartment in Bogotá, Colombia. “The defense attorney asked us to perform tests on insect specimens collected from the corpse. The tests showed that the murder had taken place only 9 hours before the body was found and not 4 days as previously thought, which led to the acquittal of the two suspects,” Wolf said.
Except for Brazil, forensic entomology is a relatively young science in most South and Central American countries, so further research is needed.
Although other methods such as the temperature method can be used to calculate the post mortem interval, if considerable time has elapsed since death or decomposition has already begun, PMI calculation may become quite complex. “Insect succession is a more accurate and reliable method for estimating PMI,” says professor Wolf, who has a PhD in Biological Sciences from the University of Granada, Spain.
The UA Entomology Group conducted a study aimed at identifying insects that are commonly associated with dead bodies. Since pig organs have shown to be compatible with the human body, researchers used dead pigs as models for human decomposition to interpret decomposition patterns.
Given that knowing the geographical distribution of insects is essential in forensic entomology, researchers studied insect species that are native to the country’s wide range of bioclimatic zones.
GEUA’s extensive database includes a complete list of insect species from different climatic zones that are associated with decomposing remains.
Between 1999-2005, GEUA conducted nearly 200 postmortem assessments for the Medellin Department of Forensic Medicine.
Today GEUA continues to provide forensic entomology services to lawyers and prosecutors across the country. Members of the Colombian General Prosecutor's Office Technical Investigation Team (CTI) or any national competent authority are required to collect samples of insects and maggots from different areas of the body and take photographs of the crime scene and submit the material to GEUA laboratory.
At the laboratory, maggots are kept alive until they reach adulthood so that the species can be determined. Half are preserved in alcohol to stop development and allow the insect to be aged.
“This procedure allows us to perform post mortem assessments and determine insect species. Our database provides us with information necessary to determine insect species and calculate the insect's age and growth curve, which is essential for estimating the postmortem interval,” Wolf said.
Flies and beetles play a significant role in the decomposition process. Blowflies are the first type of insects to arrive at dead bodies followed by other species that arrive during the later stages of decomposition. Some species prefer enclosed spaces while other insects prefer open areas. Also some species prefer light, and others prefer shady conditions. Certain types of insects will lay their eggs directly on the ground so that maggots can easily reach a buried body.
Another area covered by forensic entomology is the relatively new field of entomotoxicology, which involves the use of insects found at a death scene to test for different drugs, medications and poisons that may have possibly played a role in the death of victim.
“If there is any suspicion that death was caused by drug overdose, a toxicological analysis of the insects recovered from the body will help determine the presence of toxic substances even in decomposing bodies,” Wolf said.
Another way to identify species involves using DNA barcoding. This technique uses a short genetic market in the DNA of an organism to identify it as belonging to a particular species. Thus larvae found on dead bodies are subjected to molecular analysis in order to identify the species to which it belongs.
Recently GEUA participated in the investigation of a crime that took place in the town of Florencia, Colombia, where human remains where found by local authorities. By using forensic entomology techniques, GEUA members were able to provide accurate and reliable information to help authorities solve the crime.