Aquatic Forensic Entomology: Dr. Richard Merritt

Professor Emeritus, Michigan State University | Past President, American Board of Forensic Entomology

Dr. Richard Merritt is a towering figure in the world of entomology. While he is perhaps best known for his definitive textbook An Introduction to the Aquatic Insects of North America, his work in Forensic Entomology has provided critical evidence in high-profile homicide investigations. He specializes in using insect life cycles to solve the mysteries of “PMI”—the postmortem interval.

The Full Interview: The Science of “PMI”

When did you first become interested in forensic entomology? Actually, one of the last courses I took as an undergrad was general entomology and I loved the course because I had a great instructor. I then went on to take a course in Medical Entomology. During my undergraduate years, I drove an ambulance during the night and went to school during the day. I had a case one night in which an elderly woman’s leg had ulcerated and fly larvae had infested both of her extremities. She was semi-comatose and unfortunately died the next day. I collected and identified the flies at the scene and, at the suggestion of my professor, published an article on the situation. This was my first published paper in forensic entomology. I worked on cases with the police throughout graduate school.

What exactly does a forensic entomologist do? Basically, we try to determine what forensic scientists call the “PMI” or postmortem interval. That is the time between death and corpse discovery. We are often called on when homicides occur and are asked to determine the PMI from fly maggots and other insects found on the decomposing body. Based on temperature records and other data, we can estimate when the adult flies actually oviposited (laid eggs) on the body. From this, the time of death can be deduced.

What has been the most difficult/challenging part of your job? Trying to determine the exact PMI considering all the environmental factors. Rain, cold temperatures, whether the body is buried, or whether the individual is clothed can make a huge difference. When you are testifying as to whether someone should spend the rest of their lives in prison based on scientific evidence, you want to make sure you are correct. It is not a perfect science.

Can you give an example of a case you’ve worked on? On July 5, 1997, the dead body of a partially submerged 19-year-old female was discovered in a small lake in western Michigan. The body had been weighted down with cinder blocks and chains. It had surfaced due to gaseous build-up of decomposition. I analyzed the fly larvae collected from the head and face which were exposed to the air.

They were mature third larval instars of Phormia regina, the black blow fly. Because the body had been underwater, the situation was difficult to interpret. Based on the degree-days required for larval development, I estimated the remains were exposed to colonization between July 1st and 2nd. This matched when police suspected the victim had surfaced. An interesting aspect was the observation that tadpoles and fish were feasting upon the larvae falling into the water—the first published account of an aquatic forensic food chain.

Where do you see the future of this field? I think the best thing to do is to get a broad, general background in entomology with an emphasis on medical entomology. There are not many jobs specifically for “forensic entomologists,” so you have to sell yourself as a medical entomologist. The field is becoming more important—remember, people are dying to get into this field!!!

2026 Perspective: Forensic Ecology and Modern Tech

Since this interview, Dr. Merritt’s “forensic food chain” concept has evolved into the broader field of Forensic Ecology.

  • The Microbiome: In 2026, forensic scientists don’t just look at insects; they analyze the “thanatomicrobiome” (the bacteria of death) to refine PMI estimates even further.
  • Aquatic Succession: Dr. Merritt’s work on how long a body takes to surface in different water temperatures remains the “gold standard” for cold-case recoveries in 2026.

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