Final answer:
The first person to use insect activity to solve crimes was French doctor and entomologist Dr. Jean Pierre Mégnin, who published works in the late 19th century that became foundational for modern forensic entomology.
Step-by-step explanation:
The first person to use insect activity to solve crimes is commonly recognized as the French doctor and entomologist, Dr. Jean Pierre Mégnin. He published a seminal work in the 19th century titled 'La Faune des Cadavres', which explored the process of decomposition and the types of insects associated with decaying bodies. Mégnin's pioneering studies laid the groundwork for the field known today as forensic entomology. This disciplinary branch within forensics is vital for determining post-mortem intervals (the time since death) and other important timeline aspects in criminal investigations. With the advancements in modern research, applications of entomology have been integrated across various fields, including medicine, where maggots have been employed to clean wounds and prevent infection. Insect flight has facilitated their widespread distribution and contributed to entomology's relevancy in solving contemporary ecological issues, due to their quick response to environmental changes.