Forensic Entomology: Proper Crime Scene Collection, Preservation, and Shipment of Entomological Evidence

Jeffery K. Tomberlin¹, John R. Wallace², and Jim Olson³

¹Texas Cooperative Extension, Department of Entomology, Texas A&M University, Stephenville, TX;
²Department of Biology, Millersville University, Millersville, PA;
³Texas Agricultural Experiment Station, Department of Entomology, Texas A&M University, College Station, TX

FORENSIC ENTOMOLOGY is the study of insects and their use in investigations involving: 1) medico-legal issues, such as homicides, suicides, and other violent felonious crimes; 2) stored or commercial product issues, such as food contamination and; 3) structural damage situations, such as termite-related problems. This publication focuses solely on the medico-legal aspects of forensic entomology.

When dealing with the recovery of a decomposing human body, entomology is used for estimating a minimum postmortem interval (PMI) of the corpse. In entomological terms, this time interval refers to the time the body is colonized with insects to the time of discovery and is based on the development or succession of those arthropods on the corpse. This publication focuses on the information needed for proper entomological analysis, as well as procedures for collecting, preserving, and shipment of arthropod specimens.

DOCUMENTING THE ENVIRONMENT AND INSECT ACTIVITY: Insect activity on and around the corpse should be noted by thoroughly photographing the scene and paying particular attention to documenting insects present. It is important to note those sites on the corpse where the insects are most active. During such observations, the stage of insect development (i.e. egg, maggot, pupa, and adult) for those species present should be noted. In some instances, an investigator might have to generalize (i.e. 75% of insects present were in maggot stage) due to shear volume of insects present on the corpse. Accordingly, record the diversity of insects that are present, such as the number of different beetle species observed on the corpse.

CLIMATOLOGICAL AND TEMPERATURE DATA: Following the discovery and removal of the body, weather data should be recorded for a minimum of five consecutive days at the body recovery site. These data, along with those collected from the nearest weather station, will be used by the forensic entomologist to determine the time of development of the insects collected from the corpse and body recovery site. Basic scientific thermometers for measuring temperature are relatively inexpensive and available through commercial companies selling scientific equipment. Maggots are known to aggregate in specific sites and form a maggot mass. If possible, insert a standard meat, or scientific, thermometer into the maggot mass, record its temperature, and the location of the maggot mass on the body.

COLLECTING INSECTS

COLLECTION AND PRESERVATION OF SPECIMENS PRIOR TO MOVING BODY: If possible, collect adult flies present at the body recovery site. These flies can be collected with items such as an aerial sweep net (Figure 1) or by placing sticky cards (Figure 2) on the ground around the recovery site. Adult flies captured with an aerial net can be placed in containers (Figure 3) with cotton balls soaked in ethyl acetate or preserved in containers filled with 70% ethanol or rubbing alcohol. Once the adult flies have been collected, a representation of the immature insects or maggots will be needed. It is important to get a good representation of the various sizes of larvae present. However, be sure to collect what appear to be the “largest” maggots present. Samples of these immature insects should be partitioned into two groups. The first group can be placed in a vial with 70% alcohol (Figure 4), and the second group should be placed live in a container for laboratory rearing to adulthood (Figure 5). It is important to examine the soil beneath and around the corpse for fly larvae (Figure 6) attempting to pupate. These larvae and/or pupae can be found as deep as 10 inches in the soil. Additionally, it is important to record where these insects were collected on or surrounding the corpse. Ground dwelling insects, such as beetles, can be collected by hand or with tweezers and placed in vials or jars containing 70% alcohol. Remember to collect insect evidence from a body bag or from the morgue if the body has been removed from the scene.

REARING LARVAL FLY SPECIMENS: Larvae and eggs sampled from the body or body recovery site should be placed in an aluminum foil pouch, or other container (Figure 5), containing 10 oz or less of beef liver or a other container available. Aluminum foil pouches can be made with foil purchased from a local grocery store, but it is important not to overcrowd larvae/eggs in a pouch. A rule of thumb is to package approximately 4-6 large larvae per pouch and 20-30 eggs per pouch. Do not tightly seal the pouch, but leave it closed loosely so larvae do not escape but can breathe. The aluminum pouch should then be placed in a container that can be used for rearing, such as a plastic re-sealable container that also can be purchased at a local grocery store. It is important to remember to label these containers using the same format as discussed below. Containers with live maggots or eggs should be held in a room with constant temperatures (these should be noted on the vial label) until it is possible to ship overnight to a forensic entomologist.

LABELING AND SHIPMENT OF SPECIMENS: Dead adult insects can be placed in empty vials with a piece of dry cotton in-between the insects and lid of the vial. As previously mentioned, immature specimens collected for preservation should be placed in vials containing 70% ethanol, or if it is not available, rubbing alcohol. Paper labels should be placed inside the vial and taped on the outside (Figure 7). Labels (Figure 8) should contain the following information: case number (if available), sample number, time and date collected, collector, location on body or crime scene where collected, city or town nearest to collection site, and state. Labels should be written in pencil or Rapidograph pen ink. These are used because they will not run, smear, or disappear if moistened in alcohol. Photo documentation should be made of the location where specimens were collected. Samples and photographs should be packed in Styrofoam and cushioned properly so as not to break during shipment. Samples can be delivered in person or sent via overnight carrier (live samples collected for rearing should be shipped overnight).

ACKNOWLEDGEMENTS
The authors would like to thank P. Porter, P. Teel, and L. Tomberlin for their helpful comments on this manuscript.

Figure 1. Student using an aerial net to sample adult insects on pig carcass.

Figure 2. Sticky trap used to collect adult flies at the body recovery site.

Figure 3. Jar containing ethyl acetate used to kill adult insects collected from the body recovery site.

Figure 4. Maggots being collected from pig carcass and preserved in 70% ethanol.

Figure 5. Container used to rear maggots collected from body recovery site to adult stage. Aluminum foil pouches as discussed in the text can also be used to rear immatures to adult stage.

Figure 6. The soil where at a body recovery site can be examined for insects by using a pit fall trap (seen here) or by taking soil samples with a trowel.

Figure 7. Example of a vial containing insect specimens and 70% ethanol.

Figure 8. Example of a label, and information provided in vial containing insect specimens and 70-80% ethanol.