When the police need a time of death for a decomposing corpse, they call entomology professor M. Lee Goff. Tim Cornwell reports on a growing academic field

Insects and homicide have a long and honourable association. The villain in The Hound of the Baskervilles was a lepidopterist. A chrysalis was the killer's calling card in The Silence of the Lambs. Flies are drawn ineluctably to the dying body's odours. They arrive faster than ambulances and linger longer than funeral attendants. Insects are often the first witnesses of a crime scene, and the scientists who read their tell-tale signs are increasingly turning up in court.

Forensic entomology, the science of using insect life in postmortem investigations, in particular to determine the time of death, was first established in Europe. But in the United States, where crime and punishment is a major industry, the discipline has reached full maturity. In hard-fought US homicide cases, both prosecution and defence are likely to come armed with entomologists. Juries hear published scholars argue out the likely lifespan of those insects that infest the decomposing body.

The case of Thomas Huskey, dubbed the "Zoo Man" of Tennessee, saw one of these clashes. Huskey, known for having sex with prostitutes near the zoo, where his father worked as an elephant keeper, went on trial last February as the alleged serial killer of four women. His defence claimed, bizarrely, that Huskey was duped into confessing by one of his multiple personalities, "Kyle".

ÖйúAƬ

The body of one strangled victim, Patricia Johnson, was found on October 26 1992 and looked reasonably fresh. But Huskey had been jailed on a soliciting charge on October 21, five days earlier, and so the question of when the murder occurred was critical. Entomologist Neal Haskell, a veteran of US trials, testified that low temperatures could have delayed insect activity in the body. Entomology professor M. Lee Goff, however, called by the defence, told the court that an analysis of maggots showed the body had lain where it was found no more than three days - ruling out Huskey as the killer.

Both Goff and Haskell are members of a 15 to 20-strong core of people in the US, many of them university scholars, who double up as forensic entomologists. The group began gathering at the annual meetings of the Entomological Society of America in the mid-1980s. Aware that some colleagues found their work disgusting, they called themselves the Dirty Dozen. In 1996 they formed the American Board of Forensic Entomologists.

ÖйúAƬ

Goff is a tenured professor of entomology at the University of Hawaii, in its College of Tropical Agriculture and Human Resources. He is also a consultant forensic entomologist to the county of Honolulu and this month sees the publication of A Fly for the Prosecution, the book detailing his science and some of the crimes he has helped solve.

Hawaii through the eyes of Goff is another country entirely from that of the tourist brochures. Take the perfect morning in Pearl Harbor, when three fishermen were drawn to a two-week-old corpse by a stench worse than that of their bucket of bait. Or when a jogger on the Kawainui Marsh stumbled on a badly decomposed body infested with maggots: nearby lay a hat with a bullet hole. Children buried by fathers, wives interred by husbands, all appear with astonishing frequency. Wrapped in blankets, or clad only in running shoes, rotting corpses turn up in closets and aboard boats.

Is the Pacific paradise really a place of dark and primitive passions, of violence that strikes without warning? No, says Goff. "Really, we have a very low homicide rate. We are one of the safer places to exist." It is simply his line of work. When a body is discovered that has, to put it bluntly, been lying around a while, Goff is the man they call. He packs his folding net into the saddle bag of his Harley Davidson, along with forceps, insect containers and a camera, and roars off to the crime scene: it is important to gather insects directly from an undisturbed cadaver. Goff, by his own account, must be a startling apparition at a crime scene. When he lectured at the FBI's academy near Washington DC, his sandals, shaggy beard and diamond stud earring came as something of a shock.

In his lectures Goff compares the decomposing body to an island that suddenly rises from the middle of the ocean, virgin territory to be colonised and composted in a pattern of invasion and change. Blow flies, flesh flies and house flies are among the first arrivals; females feed on any available blood or fluids, and lay eggs or larvae.

Then follows a wave of insects: beetles, ants, bees and wasps, attracted not just by the body but as predators or parasites on the insects, eggs and maggots already feeding there. "There's something a bit surreal," Goff observes, "in the sight of dew drops glistening in the morning sun on a spider web attached to a decomposing arm."

The knack of a forensic entomologist is putting a timetable to this process. It is not an easy task. Fly eggs may take from 15 to 25 hours to hatch, according to research quoted in Goff's book. As maggots, they progress through three "instars", or phases of development, marked by the shedding of a protective outer cuticle, allowing the maggot to grow. Research suggests the first instar alone can vary from 11 to 38 hours, the second from eight to 54, the third from 80 to 112 - times vary by species. Finally, the maggot leaves the body for somewhere drier to hatch as a fly, which itself takes another four to 18 days.

A forensic entomologist must identify not just a maggot's instar and size, but also its species; this may require growing a specimen from the crime scene to adulthood. Empty pupal cases from a hatched fly, however, can help fix a minimum time that a body has lain exposed. Other factors throw calculations awry; if a body is locked in a car boot, or wrapped tightly in fabric, insects can't get at it. If the weather runs cold, flies do not fly and larvae growth slows or even stops. Entomologists, therefore, use formulas for "accumulated degree hours", a combination of time and temperature.

ÖйúAƬ

When Goff was drafted into the US army in the late 1960s, with a degree in zoology, he ended up working on autopsies as a laboratory specialist. It was that experience, he says, that predisposed him to forensic entomology.

ÖйúAƬ

It is not a subject for the squeamish. Lectures are apt to send fellow scholars heading for the door. Prosecutors are often accused of introducing insect evidence as a shock tactic with the jury, Goff says. "The defence doesn't want anyone to see photographs of the victim with maggots feeding on him."

Goff says that, in court, he isolates himself from gruesome cases by limiting his involvement to the technical details. "The interactions of insects with the body, with each other, the effects of environment, temperature, rainfall, wind, get so intriguing I tend to forget I'm working on a body," he says. "It is not the most pleasant looking or smelling thing, but it is the most natural process of recycling."

There is definitely, he concedes, an "attraction-repulsion factor" to his work. He observes people "coming into my lab who keep hoping there is something there they really don't want to see". Goff invites students on field trips to crime scenes, where he uses the corpses of pigs to teach them decomposition studies.

The Tennessee "Zoo Man" case was not Goff's first courtroom encounter with Haskell, and is not likely to be his last: the trial ended with a hung jury, and a retrial is in the offing.

Haskell claims to have collected the first PhD in forensic entomology awarded in America. While he does some teaching, he has made his living mostly in the legal system, consulting in some 75 to 100 cases a year, for a basic case fee of $350 to $600 plus $150 or $200 an hour in the few cases that reach court. He is the chief forensic entomologist consulting for the state coroner in Ontario, Canada. "In every case, there's a new wrinkle," Haskell says. "There's the challenge of trying to solve a mystery."

In Tacoma, Washington, last spring, 32-year-old Guy Rasmussen was accused of the rape and murder of a nine-year-old girl. Her body was found two weeks after she went missing, rolled in a carpet on a lot near her home. Again, the timing of the murder was critical to the alibi. Goff, with the prosecution, and Haskell, for the defence, disagreed over the effect of the carpet on insect activity. Rasmussen was sentenced to life imprisonment.

The two men also met in a case in Tennessee when Robert Glen Coe appealed against his conviction in the rape and murder of an eight-year-old girl. Haskell claimed that the absence of insect infestation was impossible to reconcile with the prosecution's case; Goff said it ruled nothing out. The appeal failed and Coe, 44, died last month by lethal injection.

M. Lee Goff's A Fly for the Prosecution: How Insect Evidence Helps Solve Crimes is published by Harvard University Press, Pounds 14.50.The 21st International Congress of Entomology takes place August 20-26. Details at American Board of Entomology: html://web.missouri.edu/cafnr/ entomology/index.html.

ÖйúAƬ