Crime Library: Criminal Minds and Methods

Kevin Neal, Convicted of Murder by Forensic Entomology

After the Blow Flies Flew Away

Comparison of Screw-worm (l) and blow fly.
Comparison of Screw-worm (l) and blow fly.

Although the blow flies had skeletonized the bodies — the maggots had eaten almost all of the soft tissue on Cody's body and a large portion of India — there were still other species of flies who prefer more decomposed flesh that Haskell could use to firm up his PMI estimates.

While Haskell was not surprised that there were no blow flies present, the fact that another species of fly, the secondary screwworm, or Cochliomyia macellaria, was also absent was especially significant. After all, the screwworm is just as adept at finding a corpse as a blow fly, and the two species prefer their carrion at similar stages. However, C. macellaria is a warm-latitude species that is killed off in northern climates when the weather turns cool. As the screwworm fly prefers fresh carrion, the absence of the fly indicates that it wasn't present in the area when the children were killed.

"It has to repopulate every spring as it warms up," he told Selvaggio during the trial.

Explaining that it takes several months for C. macellaria to reach a one-to-one ratio with P. regina — something at occurs in central Ohio around August — Haskell pointed out to the jury that the total absence of the screwworm meant the children had been dead long before the warm-weather fly arrived in Ohio.

"It tells me what time of year the colonization occurred," he told the court.

"And what time would that be, sir?" Selvaggio asked.

"It would be prior to mid-July."

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