英语听力文摘 English Digest 480、如何破无头绪凶杀案？

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Forensics

辩论术/ 法医学

A murder has been committed. The scene of the crime is a secluded area. There were no witnesses, and the body is considerably decayed.

As the chief investigator², you have a suspect who was in town a week ago. But to convict him, you'll need to know the date and time that the victim was murdered. How can you tell? And besides, what’s that annoying buzzing in your ear? Wait, don’t swat that fly! He’s your star witness. In fact, that little fly just told you the date of the crime!

Flies don’t carry pocket calendars, and they can’t testify³ before a jury. How can a crime-scene insect help a police investigation⁴? By doing what it naturally does–eating and laying eggs.

When someone dies outdoors, the first investigators⁵ on the scene are usually bright greenbottle blowflies. Attracted by the smell of decaying flesh, these usually arrive within ten minutes of the death. While this smell might make us retch, for the blowfly it’s as savory as grandma’s apple pie. The blowfly’s scientific name is “Sarcophagi,” which means “corpse eater.”

While they eat, the blowflies lay eggs in the softer parts of the body, and these hatch into maggots twenty-four hours later. These maggots attract other insects, like the predatory rove beetle（隐翅虫）, who feast⁶ on them. And so on. Wave after wave of hungry insects arrive, marking time as accurately⁷ as a clock.

Meanwhile, the blowflies follow their natural life cycle. Maggots become pupae, the pupae become adults. By surveying the insects in and around a corpse, forensic¹ scientists can help a police investigator determine how long ago a victim was murdered.