Chicago ? In a famous poem, Emily Dickinson wrote, “I heard a fly buzz when I died.”

And according to the forensic entomologists who examine murder scenes for insect evidence, there’s a good chance Dickinson eventually did.

“The first witness to a death is usually a fly,” says Mike Sarna, director of exhibitions at the Peggy Notebaert Nature Museum. “Their sense of smell is so acute that they’ve been known to fly two miles to get to a fresh corpse.”

The Chicago museum has turned a focus on flies, maggots, carrion beetles and other corpse-eaters for its new exhibition, “CSI: Crime Scene Insects,” which runs through Sept. 12.

It is not intended for the youngest or most fastidious museum-goers.

The show is curated by Lee Goff, an entomological consultant for the FBI and other law enforcement agencies worldwide, as well as for the hit “CSI” television shows. He said several plot lines for the series have come from his book, “The Fly for the Prosecution.”

Goff credits the TV shows’ popularity for the popularity of the exhibition, which already has been in St. Paul, Minn., and Roanoke, Va., and is booked solid through 2007.

Rotting pigs

The exhibition setup requires a bit more than the usual adjusting light levels. It needs plenty of fresh fly eggs, live beetles and termites. And the freezer has to be stocked with dead pigs.

Two of the pigs were lying in wire cages on a strip of lawn in back of the museum the other day. “When the exhibition opens, we’ll have five of them here, in successive stages of decomposition,” Sarna explained. “We’re just getting started with these two.”

The more pungent pig was nothing more than a pile of hide, bones and teeth.

Mike Sarna, director of exhibits at the Peggy Notebaert Nature Museum, places a speaker into a forensic entomology exhibit. The exhibit, called CSI

The fresher pig was bloated with decomposition gases, but not as smelly. A mass of maggots had already eaten the head and was boiling into the neck.

“They start at some sort of opening into the body — often the nose or mouth — and work their way in from there,” Sarna said. “If there’s an open wound with fresh blood, sometimes they’ll go in that way.”

Great precision possible

Inside, the exhibit includes morgue drawers containing two simulated cadavers showing the early and later stages of insect infestation. The “before” cadaver has fly egg masses near its nose and mouth.

“Once we know the species of the fly and the temperature, we can be very precise in finding the time of death,” said Goff, who is also chairman of the forensic sciences program at Chaminade University of Honolulu and has testified or consulted in some 300 criminal trials worldwide.

“In Hawaii,” he said, “it takes a female fly about 10 minutes to find a fresh corpse and lay eggs on it. Depending on the species, it will take from eight days to two weeks for the whole process of the maggots hatching out, eating the tissue, advancing into the pupa state and then flying off as adults.”

Forensic entomologists also rely on a “successional pattern” of insects and other arthropods that follow the maggots onto and into the corpse. Some species of mites, for example, show up early to prey on the maggots, while others hitchhike in on the shells of the later-arriving beetles and eat the byproducts of decomposition.

“We have 320 different species associated with corpses in Hawaii, so we really can fine-tune things,” Goff said.

Secrets inside

The exhibition includes two mock-ups of real cases, where visitors can use what they have learned about insects and decomposition.

One case is of two missing hikers near the Grand Canyon, where insect evidence helped prove that they drowned in a flash flood. The other is a case Goff handled in Hawaii, where the body of a gunshot victim was found in a sugar cane field. The body was infested by maggots from three species of fly — two rural and one specific to Honolulu. The urban maggots were more advanced in their life cycle, meaning that the victim had been killed in the city and dumped in the cane field.

That case involved a drug deal that went wrong. Goff said some of the most exciting developments in his field involve the use of insect evidence in drug-related deaths.

“Often, there’s not enough left of a body for toxicology tests, but we’ve learned that if the maggots have been eating tissue from a drug user, the drug traces will be retained in the pupa cases left when the adult flies hatch out,” he said. “They’re legally acceptable as evidence and we can perform toxicology tests on them.”

Such a pupa case recently aided Goff with the oldest corpse he has encountered professionally — a 500-year-old Inca mummy from Peru.

“The pupa case proved the dead person had been chewing coca leaves,” he said.