Blow flies are common insects (family Calliphoridae) that play a significant role in decomposition. They are among the first organisms to discover and begin breaking down dead tissue, acting as an important part of nature’s clean-up crew. This article explores their ability to detect deceased bodies and the factors influencing their arrival.
Initial Detection Timeframe
Blow flies can detect a dead body within minutes to an hour of death. This rapid response is primarily due to the release of specific volatile organic compounds (VOCs) that begin to emanate from a body shortly after death. These chemical cues signal the availability of a suitable site for feeding and reproduction. While detection is rapid, the actual laying of eggs often follows within minutes to a few hours, typically in natural orifices or open wounds.
How Blow Flies Detect Scents
Blow flies detect deceased bodies using a highly sensitive olfactory system. Their specialized antennae are equipped with numerous olfactory receptors that pick up minute concentrations of specific chemicals. These receptors are finely tuned to volatile compounds released during early decomposition.
Key volatile compounds that act as attractants include putrescine, cadaverine, and sulfur compounds like dimethyl disulfide and dimethyl trisulfide. These chemicals are produced as proteins, lipids, and other biomolecules within the body begin to break down. Blow flies can detect these odors from considerable distances, sometimes up to 16 kilometers away.
Factors Influencing Detection
Several environmental and circumstantial factors affect how quickly blow flies detect a dead body and lay eggs. Temperature plays a role, as warmer conditions generally accelerate both the release of attractive compounds and the metabolic activity of flies, leading to faster detection and colonization. Conversely, extreme heat can sometimes inhibit fly activity, and colder temperatures extend the blow fly life cycle, delaying their arrival and development. Humidity also influences blow fly activity, with higher humidity often enhancing their presence.
Exposure and accessibility of the body are also considerations. Outdoors and openly exposed bodies are typically colonized more rapidly than those found indoors, buried, concealed. Barriers like clothing, wrapping, or containers can delay a blow fly’s access and egg laying.
Blow flies prefer to lay eggs in natural body openings like the eyes, nose, mouth, or in any open wounds, as these areas provide moisture and protection for developing larvae. The body’s state, including freshness and presence of fluids or gases, directly impacts the types and concentrations of volatile compounds released, influencing attraction. Blow flies are also more active during bright light conditions, which influences their ability to locate remains during daylight hours.
Forensic Importance
The rapid detection of dead bodies by blow flies holds significance, particularly in forensic entomology. Forensic entomologists use the presence and developmental stage of blow flies and their larvae (maggots) to estimate the Post Mortem Interval (PMI), the time elapsed since death. Blow flies are typically the first insects to arrive at a deceased body, making their colonization timeline valuable for investigations.
The predictable life cycle of blow flies, encompassing egg, larval, and pupal stages, serves as a biological clock for investigators. Since their developmental rates depend on environmental temperatures, forensic entomologists analyze insect evidence alongside scene temperature data. This analysis allows for an accurate estimation of the time since death, often to within a few hours or a day in the early post-mortem period.