We were staring at a fuzzy photo of fly egg masses that resembled grains of rice thrown on a decaying body. “So, what do you think?” my advisor asked excitedly. As a student in one of the only forensic entomology research labs in New York City, I eagerly awaited new homicide cases that crossed my advisor’s desk. “Why don’t you and the others head down to the Office of Chief Medical Examiner (OCME) to collect samples?” my advisor communicated to me. Being a forensic entomology research lab, we used insect behavior and development to assist in legal investigations such as murders or animal abuse cases. Insects play a pivotal role in these investigations for forensic entomologists because many of them, most commonly blow flies (Family: Calliphoridae), can tell a lot about how long a body has been dead. Larval, or immature insect, developmental cycles help estimate the post-mortem interval (PMI), or the time since death; however, it is more accurately described as the minimum time of colonization (MTC). The MTC, defined as the time the first insect egg was laid, allows for a more accurate description of how forensic entomologists estimate the time of death. In our investigation, we combined a few common methods to narrow down the MTC including larval species identification and calculation accumulated degree days for development. I quickly ran to the lab and told my peers about the new case and we prepared to head to the OCME.
Once my lab mates and I made our way across to the city to the OCME, we followed an official-looking scientist into a small room, passing a few bodies covered in white sheets revealing only their feet. The scientist handed me a few vials of maggots and adult blow flies in ethanol. We carefully signed some chain-of-evidence forms and hurried back to the lab as we noticed one mistake made by on-scene investigators. The investigators did not boil the maggots to preserve their shape and morphological features. While it is possible to preserve maggots by just placing them in ethanol, long-term storage without boiling may damage defining features of species. Thus, once we returned to the lab, we drained the maggots and blanched them in boiling water. (My lab mate thought it smelled like steamed chicken…) Once the maggots were properly preserved, we had to determine the species and developmental stage of the maggots. To identify the developmental stage (first, second, or third instar), we observed the number of spiracles located on their posterior end (or better known as their butt, and yes maggots breathe out of their butt). Once we identified the developmental stage, we moved onto identifying the exact species of the collected specimens. Identifying the species becomes extremely important because each species develops at different rates, which can affect estimating an accurate PMI. Common fly families that colonize decaying animal tissue include Calliphoridae (blow flies), Muscidae (house flies), and Sarcophagidae (flesh flies) [1-3]. A typical life cycle of these flies described in the life cycle illustration occurs under controlled conditions; however, deaths usually occur in environments with varying temperatures, habitats, and other conditions that will largely affect larval development. Therefore, a professional forensic entomologist requires a deep understanding of insect metabolism and development in differing conditions, which is crucial to making accurate PMI/MTC estimations. As hopeful budding forensic entomologists, my lab mates and I cross-referenced the multiple species we identified based on morphological features and used their unique developmental timings to draw a conclusive estimation.
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