CASE HISTORIES OF THE USE OF INSECTS IN INVESTIGATIONS
Wayne D. Lord
Federal Bureau of Investigation, Washington, DC

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THE IMPORTANCE OF BLOW FLIES: EGGS, Cases 04-05

Blow fly eggs, collected from remains and analyzed, can provide investigators with an accurate estimate of postmortem interval and allow them to focus more narrowly their investigative efforts.

Blow fly eggs are small (2 to 3 mm), whitish-yellow, and somewhat elongate. During warmer seasons they are frequently packed into natural body openings and wound sites and in large numbers are easily visible to the naked eye. In temperate areas during colder months, however, their numbers may be few, and they may be difficult to locate, being more deeply recessed in cryptic locations. Blow fly eggs will typically hatch within one to three days depending on species and environmental conditions. Dissection of egg samples and analysis of the state of embryonic development may further delineate the time since oviposition and, therefore, the time of the victim's death.

Case No. 4

On a midmorning in August, the half-nude body of a young female was discovered, more or less face down, among a group of junk automobiles near Spokane, Washington. The victim had died of multiple stab wounds to the chest and neck, and adult blow flies were observed in and around the wounds. Blow fly eggs were collected from the wounds at autopsy in the late afternoon. Subsequent dissection of the eggs showed no embryonic development suggesting that they had been deposited on the remains less than eight hours earlier.

The victim had been last seen alive during the evening two days prior to her discovery. The insect evidence, however, suggested that the young woman had been murdered during the hours of darkness preceding the finding of her remains. Had the victim died any earlier, young fly larvae (maggots) rather than eggs would have been collected from her wounds. Climatic conditions on both days prior to her discovery were suitable for adult blow fly activity and egg laying. A subsequent investigation verified these findings, revealing that the victim had been murdered during the hours of darkness just prior to the morning of her discovery.

Case No. 5

In early Spring, the fully-clothed body of a young, white male was found in a sandy, shrub habitat, in the southwestern United States. The victim had died of multiple small caliber bullet wounds to the chest and back. There was little external evidence of decomposition. A small amount of blood was observed to have oozed from the victim's left nostril, partially coating his left eye.

A small irregular granular mass was collected from the surface of the victimÕs left eye. Closer examination of this substance revealed it to be a small mass of blow fly eggs. Several eggs had hatched already.

These maggots were reared to adults and were subsequently identified as Cochliomyia macellaria, the secondary screw worm. Based on the climatic conditions and knowledge of the developmental biology of this fly, it was determined that the eggs most likely had been laid on the corpse 24 to 36 hours prior to the time the corpse was found. Subsequent investigation determined the identity of the victim. He had last been seen alive in the company of a male companion approximately 36 hours prior to the time his corpse was found. It was later determined that the victim had been murdered by his companion approximately 36 hours prior to discovery of the remains.