Brazoria County Sheriff's Office

Identification Division

Analyzing the crime scene for entomological evidence

To make the most use of entomological evidence at a crime scene, an experienced and well trained forensic entomologist should do the collecting at the scene. The exact procedure at the crime scene varies with the type of habitat, but in general we can divide the work of the forensic entomologist in five parts.

1. Visual observation and notations at the scene.
2. Initiation of climatological data collection at the scene.
3. Collection of specimens from the body before body removal.
4. Collection of specimens from the surrounding area (up to 6 m from the body) before removal of the remains.
5. Collection of specimens from directly under and in close proximity to the remains (1 m or less) after the body has been removed.

Observation on insect activities at the crime scene may be useful, because the entomologist is trained in a different science than the crime scene investigators. An entomologist will probably observe elements that the investigators will ignore (and vice versa).

What should be looked for at the crime scene?

• The type of habitat the crime scene is located in? Is it rural, urban/suburban or aquatic? Is it a forest, a roadside, a closed building, an open building, a pond, a lake, a river, or another habitat type.

  The type of habitat dictates what types of insects that could be found on the body. Finding of insects typical of other habitats than the crime scene may suggest that the body has been dumped.

• Estimate the number and kinds of flying and crawling insects.
• Note locations of major infestations associated with the body and surrounding area. These infestations may be egg, larval, pupal or adult stages, alone or in any combinations of the above.
• Note immature stages of particular adult insects observed. These stages can include eggs, larvae, pupae, empty pupal cases, cast larval skins, fecal material, and exit holes or feeding marks on the remains.
• Note any insect predation such as beetles, ants and wasps or insect parasites.
• Note the exact position of the body: compass direction of the main axis, position of the extremities, position of head and face, noting of which body parts are in contact with substrate, noting where it would be sunlight and shade during a normal daylight cycle.
• Note insect activity within 3-6 m of the body. Observe flying, resting or crawling insect adults or larvae or pupae within this proximity to the body.
• Note any unusual naturally occurring, man-made, or scavenger-caused phenomenon which could alter the environmental effects on the body (trauma or mutilation of the body, burning, covering, burial, movement, or dismemberment)

Photographs should be taken of all this, with closeup photos of the different stages of insect found before collecting.

Collecting of climatological data at the scene

When estimating the PMI, climatological data about the crime scene is absolutely critical. The length of the insect life cycle is determined mostly by temperature and relative humidity in the environment development takes place.

The following climatological data should be collected at the scene:

1. Ambient temperature can be evaluated by taking readings at 0.3 to 1.3 m heights in close proximity to the body.
2. Ground temperature can be obtained by placing the thermometer on the ground, immediately above any surface ground cover.
3. Body surface temperatures should be obtained by placing the thermometer on the skin surface.
4. Under-body interface temperature can be obtained by sliding the thermometer between the body and the ground surface.
5. Maggot mass temperatures can be obtained by inserting the thermometer into the center of the maggot mass.
6. Soil temperatures should be taken immediately after body removal at a ground point which was under the body before removal. Also take soil temperatures at a second point 1-2 m away from the body. These temperatures should be taken at 3 levels: Directly under any ground cover (grass, leaves, etc.), at 4 cm soil depth and at 20 cm soil depth.

Weather data for the scene should be collected from the nearest meteorological station. Minimum requirements should be maximum and minimum temperature and amount of precipitation. Any other information is also welcome, and may aid in the reconstruction of the events. The climatological data should extend back to the time the victim was last seen.

Collecting specimens before body removal

A passive technique for collecting adult insects at the crime scene is by using sticky traps with a slow drying adhesive substance. These traps are made from waxed cardboards with a pup tent configuration set at a approximately 60 degree angle with sticky material on both exposed sides. This trap will collect many insects in a few minutes. An insect net can be used to collect flying insects. Eggs, larvae, pupae and adults of insects on the surface of the human remains should be collected and preserved to show the state of the entomological data at the time of discovery. Insects within the body should not be collected before the autopsy. If there is enough insects, samples of egg, larvae and pupae should be collected alive and placed on a rearing medium such as raw beef liver. Rearing to the adult stage makes identification easier, and may give vital clues to the PMI estimation. It is important that the temperature in the rearing container is as constant as possible, in the range of 20-27 degrees Celsius. It is absolutely necessary that the temperature is recorded in the rearing container.

In the laboratory

All samples, both live and dead specimens should now be processed as fast as possible. Live specimens are placed in incubators with known temperature and humidity levels. Several times each day these containers should be watched, and changes such as hatching of eggs or larvae, pupariation or eclosion of adult insect should be noted. The exact time should be noted. Pictures could be taken to illustrate to a jury or others. Each kind of larvae and adult should be determined to genus and species if possible. This may require the assistance of an expert of the taxon in question. It may be necessary to do experiments outdoors near the crime scene to recreate the environmental conditions for the larvae to estimate PMI.

Analyzing the data

When all the data is processed it is time to make some conclusions:

Determine whether or not the remains have been disturbed or disarticulated during the PMI. Ask if there is presence of any antemortem administered drugs such as alcohol, cocaine or heroine.

Estimate the age of as many specimens as possible, based on presence of drugs, temperature and humidity conditions. Consider whether or not insect activity was delayed after death.