COLLECTING INSECTS AT A CRIME SCENE
Not all the insects mentioned here will appear on a body in equal numbers or even be present at all. The number, type, and distribution of insects drawn to a dead body will vary by the environmental conditions, time since death, location, geography, weather, and many other factors. This is why it is important for a professional forensic entomologist to collect, process, and analyze the insect data from a death scene: It is a complicated and specialized discipline. Because of this variability in the number and kind of insects, the information they provide can sometimes be quite precise as no two scenes are exactly alike in time or space. Forensic entomologists encounter a diverse range of habitats and conditions when assisting with crime scenes. It is important that all personnel from the various agencies at a death scene cooperate with the primary investigating agency and be aware of each person’s assigned responsibilities. This is especially true for the forensic entomologist because many police agencies are not familiar with this science and its requirements for evidence collection. The entomologist should discuss with the evidence technicians and the primary investigator the plan for evidence collection and the role the entomologist intends to play. The following is a suggested sequence of stages for a forensic entomological investigation (Haskell et al., 2002):
- Visually observing and taking notes of the scene
- Recording notes
- Approximating the number and kinds of insects
- Recording locations of major insect infestations
- Noting immature stages
- Identifying the precise location of the body
- Observing any other phenomena of note (trauma, coverings, etc.)
- Collecting climatological data from the scene
- Recording ambient air temperature
- Measuring ambient humidity
- Taking ground surface temperature
- Taking body surface temperatures
- Taking below-body temperatures
- Taking maggot mass temperatures
- Taking postbody removal subsoil temperature
- Collecting specimens from the body before its removal from the scene
- The area surrounding the body (up to 20 ft) before its removal
- Directly under the body after the body has been removed
Necrophilous insects, particularly flies, are attracted to dark, moist areas: On fresh bodies, this means the face (nostrils, mouth, eyes, etc.) or any open wounds, shown in Figure 1.
FIGURE 1 Insects that are attracted to dead animals as an environment for food and reproduction (necrophilous) usually inhabit dark, moist areas first, like the eyes, mouth, nose, and open wounds.
The genital or rectal areas, if exposed or traumatized, will sometimes provide shelter and moisture for ovipositing flies. The entomologist should record the patterning and number of ovipositing and larvae with notes, drawings, and photographs. Insects can be collected in a variety of ways, most of which will be employed at every death scene. Flying insects can be trapped in a net by sweeping it back and forth repeatedly over the body. The end of the net, with the insects in it, can then be placed in a wide-mouth killing jar, a glass jar containing cotton balls soaked in ethyl acetate. Several minutes of exposure to the ethyl acetate will kill the insects; they should then be placed in a vial of 75% ethyl alcohol (ETOH) to preserve them. Two labels should be prepared for each specimen (one for inside the vial and one for the outside), and they must be written in pencil; ink may dis solve in the ETOH. Crawling insects on and around the body can be collected with forceps or fingers. The entomologist must be careful not to disturb any other potential evidence while collecting insects. If the body will be put into a body bag, it is a good idea to check for any insect activity before the body is placed inside it. Eggs and a mixture of larvae of various sizes (several hundred in total) should be collected, as well as any adults. A portion of the larvae should be preserved the same as described for flying insects; another portion should be kept alive to rear to adulthood. If the entomologist is collecting the insects in the morgue, a careful inspection of the clothing must be made in conjunction with the forensic pathologist’s observations. Once the body has been removed, the soil under the body should be sampled. An approximately 4″ × 4 × 4″ cube of soil (about the size of a one-pint ice cream container) should be taken from areas associated with the body, such as the head, torso, limbs, or wherever seems appropriate given the body’s position. Additional soil samples should be taken up to 6 ft from the body in each direction. Any plant materials associated with the body or its location should also be collected for possible botanical examination.
Buried or enclosed remains present particular problems for the entomologist because insects’ access to a body is limited. Some flies are barred from a body by as little as one inch of soil. Burial also slows the process of decomposition due to lower and more constant temperatures, fewer bacteria, and limited access to the body. A building can also prevent some types of insects from gaining access to a body or slow down their recognition of the chemical odors that signal decomposition. This alters the entomologist’s estimation of time since death because the “clock” of insect succession rate has been altered. However, the odors may escape, but the insects may not be able to gain access: Finding a cloud of flies hovering above a car trunk may indicate that a dead body has been in there for some time. If the structure is a house or an apartment, then weather data probably will not help the entomologist devise a time since death. Rather, the thermostat settings could be substituted for “climate” data. Another example would be a car with the windows up during the summer, where the internal temperature even on a mild day can easily reach in excess of 110 °F. In short, any environmental change, whether natural or artificial, needs to be measured and noted for the entomologist to make an accurate estimate.
Wide-angle and close-up photographs should also be taken, with emphasis on specific areas of insect activity. The forensic entomologist should, after returning to the laboratory from the scene, begin collecting weather data for the period of time in question.
