Forensic Entomology and Crime Scenes
Dave Carlson - September 1, 2006
Bugs can’t keep a secret. Their presence and development can record volumes of valuable clues decipherable by a trained forensic entomologist. “Forensic entomology is the name given to the study of insects (or even other arthropods such as mites and ticks) that form part of the evidence in legal cases, but is mainly associated with death enquires” (Amendt et al., 2006, p. 1).
Insects can play a significant and very noticeable role in the decomposition of soft tissue after death. “Insects are not only of ecological importance in decomposition, but are extremely valuable in death investigations” (Haglund & Sorg, 2002, p. 174). Forensic investigators in Europe have know about the importance of studying insects on decaying bodies for about 150 years, but it is a relatively new field of study in North America, having been commonly used in death investigations for only about 30 years (Haglund & Sorg, 2002, p. 174).
Collecting insect specimens at a death scene to preserve physical evidence follows basic procedures used by entomologists in normal specimen collecting activities. Some entomological procedures have been modified for use in a forensic context to “enhance the ultimate evaluation of insect evidence” (Haglund & Sorg, 1997, p. 437). Entomological evidence is becoming increasingly more important in forensic investigations. To that end, the European Association for Forensic Entomology (EAFE), an international body of physicians and scientists, compiled a list of best practice standards in forensic entomology (Amendt, et. al., 2006, p. 1).
Here are the standards for best practice forensic entomology ratified by the EAFE during their third annual meeting in April 2005 in Lausanne, Switzerland (Amendt, et. al., 2006).
- Use 70-95% ethanol to preserve specimens and, for health and safety reasons and because tissues are less well-preserved for morphological and molecular identification, do not use formalin/formaldehyde (p. 2).
- Killing is recommended for ALL sampled specimens when the use of the insects for the enquiry is ambiguous at the time of collection and/or rearing is impossible (p. 3).
- Maintain living insect samples under known temperature conditions (p. 3).
- Always check the corpse AND the surrounding for entomological evidence (p. 3).
- Sample different regions of the corpse and collect the evidence into different labeled vials (p. 3).
- Collect the most mature insect specimens that have developed on the corpse (adult, puparia, pupae, post-feeding and feeding larvae, or eggs) and remnants, such as empty fly puparia or beetle exuviae (p. 4).
- Only use reliable temperature data to estimate a time of death based on the development stage of the insects (p. 4).
- Rear all stages under conditions of temperature and humidity that are controlled and recorded (p. 5).
- Identify immature specimens (especially larvae) using reliable identification keys and establish the most mature individual available in the sample. For larvae, for example, record the stage of development (first, second, third, post-feeding, pre-pupae) (p. 5).
- Before aging the specimens, they must be identified to the correct species using reliable identification keys (p. 7).
- To age fly larvae, it is essential to:
- (1) Measure the size of the larvae (length and/or weight), their stage of development (first, second or third instar) and determine whether they are feeding or post-feeding.
- (2) Accurately determine the temperatures to which the larvae were exposed during their development either on or off the body.
- (3) Relate the size and feeding stage of the larvae to their age using suitable experimental references or a database of size and stage against age at different temperatures (p. 7).
- Give the minimum duration of development for the oldest stage of insect (p. 10).
Insect specimens collected during a crime scene investigation or autopsy should be collected and processed as physical evidence with the same care given to “blood stains, fingerprints, hair, fibers, or any other biological material” (Amendt, et. al., 2006, p. 1). Collecting, preserving, and packaging insect specimens must be conducted in a systematic and quality-assured manner “not only to prevent contamination or destruction of evidence and to guarantee the chain of custody, but also because forensic entomology deals with living organisms, which should be treated with care” (Amendt, et. al., 2006, p. 1).
It is important to ensure collection activities at the crime scene do not contaminate the insect evidence. A best practice during evidence collection is for the entomological investigator to wear protective clothing, especially when removing specimens from the corpse and immediate crime scene. In addition to protecting the investigator, protective clothing helps “avoid any contamination of the scene with fibers or other material from the investigator” (Amendt, et. al., 2006, p. 2). Amendt (2006) recommends minimum protective accoutrements consist of overalls, gloves, and shoe covers or boots (p. 2).
To supplement standards already listed, Amendt (2006) recommends that live samples should be transferred for rearing with 24 hours or killed as soon as possible (p. 3). The recommended method for killing specimens is to immerse them in very hot (>80°C), but not boiling water, for about 30 seconds for ideal preservation (p. 3). “All procedures should be undertaken as soon after collection as possible and with all times recorded” (p. 3).
It is important to note that all collection of insect evidence and temperature data taken at the crime scene or during an autopsy must be done with specific authorization of the person in charge (Amendt, et. al., 2006, p. 3). Amendt (2006) also points out that it is extremely important to ensure the forceps or instruments used for collecting insects do not inadvertently inflict postmortem artifacts on the corpse (p. 3). Inadvertent nicks could mislead other investigators.
Amendt (2006) provided an overview of entomological methods to estimate stages of the postmortem interval using insects, highlighting important do and don’t principles (p. 11). He concludes with a charge to forensic examiners to work together closely to collect and preserve insect evidence which helps paint a vivid picture of perimortem and postmortem events (p. 11).
Amendt, J., Campobasso, C. P., Gaudry, E., Reiter, C., LeBlanc, H. N., Hall, M. J. R. (2006, April 22). Best practice in forensic entomology - standards and guidelines. [Electronic version]. International Journal of Legal Medicine, online version. Retrieved September 1, 2006, from http://www.springerlink.com/content/172638713119r683
Haglund, W. D. and Sorg, M. H. (Eds.) (1997). Forensic taphonomy: The postmortem fate of human remains. Boca Raton, FL: CRC Press.
Haglund, W. D. and Sorg, M. H. (Eds.) (2002). Advances in forensic taphonomy: Method, theory, and archaeological perspectives. Boca Raton, FL: CRC Press.