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Factory Breeds Man-Eating Flies


Aug 19, 2002
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Grisly Mexico Factory Breeds Man-Eating Flies
Fri February 21, 2003 10:17 AM ET

By Elizabeth Fullerton
TUXTLA GUTIERREZ, Mexico (Reuters) - Tucked away in southern Mexico's jungly Chiapas state, scientists work around the clock using radiation and powdered blood to produce one of the area's most cutting-edge exports -- man-eating flies.

Tuxtla Gutierrez, the capital of Chiapas, better known for spawning an armed rebellion in 1994 by guerrillas fighting for Indian rights, is home to the world's only New World screwworm plant, breeding millions of insects each week.

Named for the corkscrew motion with which they burrow into flesh, the screwworm larvae can kill their victim -- human or animal -- in five days. The worm's Latin name, cochliomyia hominivorax, means "fly that devours men."

"They feed off fresh blood, not dead tissue as other species do. That's why they are extremely dangerous. It's very hard for an animal to defend itself against something like that," said Alfredo Alvarez, a biologist at the plant.

In the 1950s, U.S. scientists pioneered a strange but effective way of eradicating the pests. The flies are zapped with high doses of radiation to sterilize them then released into the wild to mate with their fertile counterparts.

The females only mate once, so if they do so with the sterile flies, they will not reproduce.

Using this technology, the United States by 1982 wiped out the bug that had threatened swathes of the nation's livestock.

With the aim of gradually eradicating the worm from the American continent, the fly-producing factory in southern Mexico was started in 1976 by a joint U.S.-Mexican government commission and by 1992 Mexico was declared free of the screwworm.

But there have been recurrences in Mexico recent years, some, ironically, due to errors at the fly factory that allowed millions of the killer flies to escape.

Machine failure at the plant caused an outbreak of the disease in January that Alvarez described as a "disaster."

But thanks to the 27-year-old plant, the flies have been mostly wiped out in the southern United States, Mexico, Libya and across most of Central America.

In the early 1990s, Mexico exported the flies to Libya, which was contaminated by South American cattle imports.

The U.S.-Mexican commission is now selling its unusual product to Panama and Jamaica, where what look like cardboard lunch-boxes packed with black buzzing flies are dropped from planes to rid those areas of the bloodthirsty insect.


A fetid, overbearing stench of decay -- the odor from the waste that about 90 million flies produce each week -- hits a visitor on arrival at the fly plant.

It pervades clothing, hair and nostrils long after one leaves the plant, despite obligatory rigorous showering.

Security is tight. All visitors and personnel are given clean overalls and boots for entering the production area, which is locked after them and has no windows.

In the so-called "fly colony," a loud buzzing emanates from row upon row of metal cages where thousands of fertile flies are kept alive and fattened for breeding.

To the untrained eye, they resemble common house flies with blue-green bodies but these have bulging orange eyes.

After seven days, the flies are mature enough to lay their eggs and are taken to a darkened room. They lay their eggs along long wooden sticks smeared with a gel that to them smells similar to a wound. The fly's average life cycle is 20 days.

One fly can lay up to 400 eggs in a wound. Within 24 hours these hatch into larvae and begin burrowing into the meat.

In two days, an open sore in an eye, for example, will turn into a grapefruit-sized festering wound of raw, pulpy flesh. The larvae eat their way toward the victim's vital organs.

"If the wound is in the stomach, they'll try to get to the liver or intestines. If it's in the head, they'll attack the eyes, the ears. They can reach the brain and then it's adios," said Alvarez, who is employed by the U.S. Department of Agriculture's Agricultural Research Service.

The worm comes in two species -- the New World screwworm, native to the Western Hemisphere, and the Old World screwworm, found in Southeast Asia, the Middle East and parts of Africa.


In the incubation room, live wounds are mimicked in racks of hundreds of trays, using a brown gel containing powdered blood, milk and egg among other ingredients.

Workers scrape the fly eggs off the wooden sticks and deposit them in these trays on top of a piece of paper towel.

As they hatch into larvae, tiny white grubs begin to swarm over the brown muck. "They are totally convinced they are attacking a warm animal," said Alvarez.

Within 48 hours, the grubs have grown fatter and their diet must be replenished. "This is equivalent to a worm moving to another zone of the body to find fresh flesh," said Alvarez.

From a distance, the huge trays resemble baking trays of brownies but at close range the mixture bubbles with the gouging and squirming of around 20,000 worms per tray.

By the third day the trays brim with thick brown-red goo as more gel is added to satisfy the worms' rapacious appetite. The smell is at its most rancid.

As they reach maturity, the grubs jump out of the trays, falling into funnels where they are scooped up and poured by the thousands into trays with sawdust covering them. They are left for 24 hours to develop a shell and become pupae.

After five and a half days the pupae are put in plastic cylinders and exposed to around two minutes of radiation. The amount of radiation is 11 times the minimum needed to kill a human being but the flies are tough.

Once they have been irradiated, the pupae are placed in ice coolers to slow the process of their maturing into flies.

The high-tech plant, a rarity in the impoverished and heavily agricultural state of Chiapas, exports the "chilled flies" twice-weekly to Panama and Jamaica.


The United States now plans to build a plant in Panama to create a sterile fly barrier against flies from South America.

But the story has its failures too.

Despite stringent security procedures such as numerous fly traps in and outside the plant, special clothing and the stationing of boxes of sterile flies around the perimeter to mate with fertile escapees, there have been outbreaks.

Last month, the plant had its worst ever when a radiation machine malfunctioned. Millions of fertile flies were sent into the wild in Mexico and Panama. To date 50 cases of the disease have been found in animals in Panama and 44 in Chiapas.

The damage could escalate and take months to repair.

"It's a disaster for us. We're on national alert," said Alvarez. "The outbreak gives us an inkling of what could happen if the flies were used as a biological weapon in a terror attack. It could be very dangerous."

I love technology ;)


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