Editorial-Opinion November 2016

The news is devastating, threatening and shocking, yet completely predictable. New World screwworm has appeared in the endangered Key deer population on Big Pine Key in Florida. Screwworm has already killed 5 to 10 percent of the estimated 1,000 Key deer, and endangered subspecies of white-tailed deer. 

But screwworms present equal-opportunity threats to all deer and indeed all mammals, throughout North America, including humans. They were the scourge of wildlife and livestock until the 1950s when science learned how to control the pest, eradicating the threat from the northern hemisphere in the mid 60s. 

Screwworms are a threat because, unlike other fly maggots that eat dead flesh, the screwworm maggot eats live flesh. The female needs to breed only once in her life cycle to lay all the eggs she will lay in her short-lived adulthood. She seeks any wound in which to lay her eggs, and the body heat of the wounded host incubates the eggs in about 10 hours. As soon as the eggs hatch, they begin to eat into living flesh, screwing themselves into the flesh and often causing death to the unfortunate host. 

Whitetail bucks are particularly impacted by screwworms because the tender velvet of their horns in the late summer, and then especially the raw wound from when they drop antlers, provide an ideal entry point for screwworm infection.

The key to controlling this horrid affliction lies in understanding their sex life. As it turns out, the male screwworm fly lives to breed with any female fly it can find and as many female screwworms as it can find. Quite opposite, the female screwworm breeds only once in her life, and with only one male screwworm fly. In a manner similar to a female turkey, she can hold those sperm for multiple episodes of egg-laying. 

So, if one wishes to stop the egg-laying of a screwworm fly, one only needs to have her accept the mating of a sterile male screwworm fly. After that mating, she is effectively rendered infertile, simply because all of her eggs remain unfertilized. 

The program of utilizing sterile male screwworm flies is fairly straight-forward. During the 1950s and 1960s, millions of these sterile flies were released across the south and west, and the screwworm population crashed. 

Screwworms remain in South America, and there is what amounts to a blocking operation in Panama where continual production and release of male screwworm flies maintains an effective roadblock to those flies migrating back north. 

And yet, they are here… again. 

Increased travel, and increased cultural and biological transportation, make this sort of consequential outbreak almost inevitable. 

Because there already exists a ready supply of sterile male screwworms in Panama, there is a proven course that hopefully will stem the current infection in the Keys.  

It is, however, the latest example of the mixing of flora and fauna into environments where either they previously did not exist, or have, like the screwworm, been previously extirpated from their original range. 

There are other examples that come to mind. 

The most recent example is the Zika virus that has moved from central South America with such remarkable impact. Yet it pales in comparison to HIV, which came from Africa. West Nile Virus moved with its own host mosquitoes to our swamps and flower pots. 

And all of this is just the latest in a growing, incoming tide of these health and environmental assaults. 

There are python hunts in the Everglades. 

Bigheaded carp are threatening the entire Great Lakes ecosystem, and lion fish threaten our saltwater reefs. 

There is, of course, the imported fire ant. Coyotes and armadillos have vastly expanded their range. 

There is a long, inglorious list—unfortunately a growing list—of these unwelcome world travelers. 

It is necessary that we continue to do our part as sportsmen to fund the science and systems that are our defense; the defense of, in this instance, our deer herd. 

We stand a lifetime removed from the scourge of screwworm, and yet it is with us again. And we have been faithful for all these years.