roof rat

A roof rat noses around a rodent bait station on Kiawah Island in August 2020.
Image Credit: Eric Benson, Clemson University

CLEMSON — Dogs may be man’s best friend, but rats have been his constant companion. For good or ill — more often the latter — rats have followed us wherever we go. Even luxury gated communities are not immune.

Rodenticides — chemicals that kill rodents — are a significant tool in the fights against rats. But pest control operators are looking to amend their arsenal with additional weapons on South Carolina’s Kiawah Island, where some of the community’s famous bobcats have tested positive for the chemicals.

In an August 20 online training held by Clemson University, pest control professionals representing 85 percent of the properties with pest control service on Kiawah and tens of thousands across the state studied ways to incorporate a variety of methods to reduce the reliance on chemicals and, as chief speaker Donny Oswalt said, “still provide a high level of control without adversely affecting the environment.”

The approach is known as Integrated Pest Management (IPM) and has been used in pest control for generations, especially on farms. President Nixon mandated its teaching for use on row crops in the 1970s. But the process is especially complicated on Kiawah, a rapidly growing residential environment in what was once a marshy habitat for bobcats and the rodents and other wildlife they feed on.

Kiawah home

Many homes on Kiawah Island are surrounded by dense vegetation, drawing a fine line between the habitats of humans and wildlife.
Image Credit: Eric Benson, Clemson University

“Kiawah is a very sensitive environment, a complex environment. There are thousands of structures basically in a jungle. Other resort areas in South Carolina are similar,” said Eric Benson, an emeritus professor and Clemson Extension specialist whose expertise is IPM for urban pests. “Thankfully we can use a diversity of tools — and we have a lot for rodent control — and reduce non-target exposure.”

The enemy on Kiawah is chiefly the roof rat, so named because of the ease with which it climbs. Also called ship rats, the rodents are frequently found near ports and seashores but have spread widely in the United States. They’re also a tasty treat for bobcats.

“Roof rats have displaced the most prominent pests in northeast Alabama where we are located and we’re a long way from any coastal cities or seaports,” said Oswalt, a Clemson University Ph.D. graduate and specialist in rodent IPM with more than 40 years of experience. He owns an Alabama pest control business, The Bug Doctor.

“They are agile climbers. They certainly would have no trouble scaling the buildings built above ground-level on coastal islands,” he said. “They deposit urine and/or feces and secretions on frequently used pathways that have a type of pheromone used as a form of communication so great-granddaddy can let future generations know he was here — a few months ago.”

Oswalt doesn’t exaggerate. With a life span of 5 months to 1.5 years a female roof rat can have 4 to 8 pups per litter in 3 to 4 litters per year. Multiply that times as many as 180 pellets of poop per day and the need for rodent control is painfully clear.

“The list of diseases these rodents can vector is jaw-dropping. Roof rats eat our food, foul our food, spread disease,” Benson said. “From the monitoring I have done on Kiawah — just a few nights, so it’s only anecdotal — the only rodents I saw were roof rats. It seems like mice are not much of a problem, because rats wreak havoc on other species. It’s very important to understand what rodent or rodents you have, because control strategies can be very different.”

Kiawah trash

It doesn’t take much access to food, water or shelter to support rodents such as roof rats. Small amounts of trash, such as this at a Kiawah Island commercial business, will draw pests.
Image Credit: Eric Benson, Clemson University

Pest control operators work with homeowners and business owners to settle on the appropriate strategies for each individual case. Many don’t involve rodenticide at all. Proper sanitation is step one. “Everyone has trash,” Benson said.

“Kiawah is a very unique habitat with homes carved out of the natural landscape. You’ll have a very small interface between where the natural vegetation stops and the homeowner environment starts,” Oswalt said.

“One of the techniques we use is to make the habitat inhospitable for roof rats: reduce overgrowth from vegetation that may harbor rats, reduce clutter, eliminate man-made water sources and opportunities for roof rats to forage,” he said.

Grandpa’s old snap-traps still work just fine, but they may be incapable of putting a dent in a fast-growing rodent population.

Chemical agents often are used because they can work quickly and reach more rats at a time than mechanical traps can.

After centuries of using various poisons to eradicate rats, humans developed a new kind of chemical in the 20th century: anticoagulants. These rodenticides will make rats bleed to death internally by using a two-pronged approach: damaging blood vessels and keeping their blood from clotting, hence the name.

The first generation of these rodenticides like warfarin and chlorophacinone appeared in the 1950s. To be effective these must be used in higher concentrations than more modern chemicals.

Faster-working, more toxic second-generation anticoagulants, known as SGAs, appeared in the 1970s and fast became the preferred chemical control agent.

It is these SGAs the biologists discovered in the Kiawah bobcats, leading island residents, pest control operators and Clemson experts to seek solutions.

“We are still collecting company-client information for the town, but we are confident that pest control companies have voluntarily moved at least 70 percent of the town accounts away from SGA use,” said Steve Cole, director of Regulatory Services at Clemson, which houses the state Department of Pesticide Regulation and other state regulatory agencies.

Many have embraced IPM.

“We can’t think of this as a singular issue. We have to look at how we strike a balance,” said Jim Wright, executive director of the South Carolina Pest Control Association. “Use of rodenticide is one of the tools in your toolbox. You need to think a little out of the box.”

Kiawah construction

Construction continues on Kiawah Island, carving new lots out of natural areas.
Image Credit: Eric Benson, Clemson University

Asked during his presentation whether reverting to the first-generation anticoagulants might be preferable, Oswalt urged caution.

“All rodenticides have their own inherent risks. In many cases, I feel safer with SGAs for my clients. In my experience, pets that accidentally ingested SGAs came out better than with the non-SGAs,” Oswalt said. “If a homeowner’s prize-winning poodle ate bait you put out, the homeowner is not going to give a hoot about a wild animal. She’s not going to come and thank you because you protected wildlife and yet her dog died.”

All the parties involved agree on one thing: More research is needed to get to the bottom of the problem.

“We are pleased with the initial efforts and collaboration from Clemson and the pest control industry, but we also know that more work is needed to reach our goal of 100 percent removal of SGAs from the island,” said Town of Kiawah Island Mayor Craig Weaver. “The initial research efforts from Clemson will help us determine the progress from these voluntary measures and may help the town identify other issues that might need attention.”

Jim Jordan, a wildlife biologist for the town, noted that the decline in the island’s bobcat population began around 2017. “We’ve been tracking these animals for 20 years and haven’t seen this problem,” he said. “Obviously, something has changed, but we don’t know what it is.”

“It’s critical for us to move forward and answer the question about the use of SGAs in the Kiawah ecosystem,” Wright said. “At the end of the day, we may be able to reduce the use of SGAs in that ecosystem.

“We like the idea of an integrated approach,” he said. “That, by its very nature, takes into account lots of things than can affect the outcome. It is not one-dimensional.”

END