Environmental effects on forensic entomology
Forensic entomology, more specifically its medicocriminal branch, has evolved since the first days of its implementation. Yet, the field is still growing and daily, new information and techniques are being attempted to help entomologists more accurately report vital information such as post mortem intervals. There is a standard accepted theory that outlines eight distinct faunal successions, which will be eluded to later in the article. However, what happens when during decomposition the maggot mass found on the body differs from what should be expected? It is the forensic entomologist’s job to determine the level of difference from the norm and to scientifically account for the deviation.
Climate
Moisture levels
Rain and humidity levels in the area where the body is found can affect the time for insect development. In most species, large amounts of rain will indirectly cause slower development due to drop in temperature. Light rain or a very humid environment, by acting as an insulator, will permit a greater core temperature within the maggot mass, resulting in faster development.[1]
Sun exposure
"Because insects are cold-blooded animals, their rate of development is more or less dependent on ambient temperature." [2] Bodies exposed to large amounts of sunlight will heat up, giving the insects a warmer area to develop, reducing their development time. In one experiment conducted by Bernard Greenberg and John Charles Kunich with the use of rabbit carcasses to study accumulation of degree days found that with temperature ranging in the mid 70s to high 80s the amount of deveopmental time for maggots was signifigantly reduced. [3]
In contrast, bodies found in shaded areas will be cooler, and insects will require longer growth periods. In addition, if temperatures reach extreme levels of cold insects instinctively know to prolong their development time in order to hatch into a more accepting, viable climate in order to increase the chance of survival and reproduction.
Climate measurement
Important concepts in forensic science are threshold temperature and degree days.
- For each type of insect, development will not occur unless the surrounding temperature is above the minimum threshold for that insect.
- A given amount of thermal energy is needed to develop from one stage of an insect life cycle, such as egg laying or egg hatching, to the next. This is measured as degree days. The degree days in a specific location over a specific period is calculated as the mean of the minimum and maximum temperature, minus the threshold temperature, mulitplied by the number of days.
Observations of the life stage of the insects present, in combination with the calculated degree days, can be used to estimate the post mortem interval.
Geographic distribution
According to Jean Pierre Mégnin's book La Faune des Cadavres there are eight distinct faunal successions attracted to a corpse. While most beetles and flies of forensic importance can be found worldwide, a portion of them are limited to a specific range of habitats. It is forensically important to know the geographical distribution of these insects is order to determine information such as post mortem interval or whether a body has been moved from its original place of death.
Calliphoridae is arguably the most important family concerning forensic entomology given that they are the first to arrive on the corpse. The family’s habitat ranges into the southern portion of the United States. However, while Chrysonoma rufifaces, the hairy maggot blow fly, is part of the Calliphoridae family and is widespread, it is not prevalent in the Southern California, Arizona, New Mexico, Louisiana, Florida, or Illinois regions.[4]
Flesh flies fall under the family Sacrophagidae and generally arrive to a corpse following Calliphoridae. However, their ability to fly in the rain enables them to occasionally reach a body before Calliphoridae. Flesh flies are globally distributed including habitats in the United States, Europe, Asia, and the Middle East. [5]
Beetles are representative of the order Coleoptera which accounts for the largest of the insect orders. Beetles are very adaptive and can be found in almost all environments with the exception of Antarctica and high mountainous regions. The most diverse beetle fauna can be found in the tropics. In addition, beetles are less submissive to temperatures. Thus, if a carcass has been found in cold temperatures, the beetle will be prevalent over Calliphoridae.
References
- ^ "Forensic entomology: use of insects to help solve crimes". Uwa.edu.au. 20 March 2008.
- ^ Catts, E. P. and N. H. Haskell, eds. Entomology & Death: A Procedural Guide. Joyce's Print Shop, Inc. 1990. p5.
- ^ Greenberg, Bernard, and John C. Kunich. Entomology and the Law. United Kingdom: Cambridge University Press, 2002.
- ^ Whitworth, Terry. "Keys to Genera and Species of Blow Flies of America North of Mexico." Proceedings of the Entomological Society of Washington 108.3 (2006): 710.
- ^ Pape, Thomas. Catalog of the Sarcophagidae of the World. Memoirs on Entomology. Gainesville, FL: Associated, 1996. 288-289.