A “Screwy” Success Story

Part 8:


A part of history that is not as common – or not talked about much – is the eradication of the screwworm that caused a lot of damage to the cattle herd (and humans!) in the past. For all of the reasons listed below, the story of screwworm eradication is one of the great success stories of science and of cooperation among farmers and governments.

I will post portions of the article here, but you can find out more of the history by Alan Newport, full story here.

The Most Hideous Creature
Screwworm eradication great story of science and solidarity.
By Alan Newport

The screwworm, for most people who remember it, was one of the most insidious and grotesque creatures the Creator put on this earth. For those unfamiliar with this now-eradicated pest, the maggot eats only live flesh.

Knife castrations had to be treated with pine tar oil and watched closely.

Young animals born during fly season almost universally needed their navels treated to prevent screwworm infestation.

Threats came from all sides: sheep and goat shearing, dehorning, ear wounds from Gulf Coast ticks, wounds from rough handling or shoddy corrals, branding, dog or predator bites.

By 1950 the screwworm had spread as far north as South Dakota via infested livestock.

Sometimes even people would be infested, often through their sinus cavities.

In the 1930s, Agricultural Research Service scientists Edward F. Knipling and Raymond C. Bushland concluded reducing or eliminating the screwworm fly population was a better solution than treating the pests topically after entry into hosts via skin wounds.

The Southeast U.S. was declared free of screwworms in 1959, and the Southwest in 1966. Texas remained partially infested until 1982. In 1991 Mexico was declared screwworm-free. The project kept pushing south, and in 2000 Costa Rica was declared screwworm-free.

Fast reproduction
The screwworm fly is native to tropical America. A blue-green blowfly with three dark stripes on its back, it looks a lot like the other blow­flies on this continent. The difference is, the screwworm fly only lays eggs in living flesh.

A female can lay 3,000 eggs in her two-month life span. Those eggs hatch in nine to 24 hours, and the maggots begin burrowing into and eating the host animal’s flesh. In five to seven days, the maggots are full grown and leave the wound, dropping to the ground and burrowing into the soil. They turn rapidly into a reddish-brown pupae and stay in the soil for seven to 14 days.

When the adults hatch, they crawl up on vegetation to dry and harden, and then fly out looking for prey. The progeny of a single female can mount to thousands of new flies and mag­gots in a few months.

Treatment woes
Treating wounds in early years required cleaning them and then pouring in commercial benzol or chloroform. After that, the recommendation was to put a cotton ball dampened with benzol into the wound and leave it there to drop out on its own. The area around the wound was also to be treated with pine tar oil to discourage adult screwworm flies from landing there.

In 1938 USDA developed Smear 62, a thin paste formed from a combination of diphenylamine, benzol, turkey red oil and lampblack. It was an improvement but still required diligence in treatment and in watching animals for wounds and infestation.

A good and brief history of the screwworm and the eradication program is available online HERE.

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