10 Most Destructive Pests in the U.S.

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So you found a few rat droppings in your pantry recently and think you have a pest problem. It could be much, much worse. One Indiana town in 2014 discovered that a lowly ground squirrel had caused a $300,000 meltdown in the electrical and HVAC systems in a new community center. Pests are everywhere, it seems, and while homeowners set out baits and traps or call exterminators, pests cause billions of dollars of damage in the U.S. each year. Here’s our take on the most destructive pests in the U.S., taking into consideration not just the financial toll but ecological damage as well.


10. Squirrels

Despite their harmless appearance, squirrels can damage crops, electrical wiring and more. © Corey Seeman

Despite their harmless appearance, squirrels can damage crops, electrical wiring and more. © Corey Seeman

Most everything you’ve ever heard about the potential threat of squirrels is true; they can, in fact, get into an attic, chew through electrical wiring and start a house fire. It’s relatively rare, but that’s little consolation if it is your house going up in flames. They cause thousands of power outages across the country each year. Squirrels also carry disease; some squirrels carry bubonic plague. These rodents cause other, less obvious problems, damaging crops, destroying irrigation lines, and gnawing on fiber optic lines.


9. Burmese Pythons

A Burmese python battles an alligator in Florida's Everglades. Credit: Lori Oberhofer/ National Park Service

A Burmese python battles an alligator in Florida’s Everglades. Credit: Lori Oberhofer/National Park Service

These giant snakes, which can reach more than 20 feet in length and 250 pounds in size, are well established in Florida’s Everglades, where they are gobbling up native species, including foxes, alligators and even the endangered Florida panther. We’re not talking just a few hundred or several thousand of these snakes on the loose; one estimate puts the number of pythons in the Everglades at around 150,000. If you live in one of the other 49 U.S. states, you may shrug that off as “Florida’s problem.” Unfortunately, the Burmese python is slithering its way out of the Sunshine State. It’s already been found in the Florida panhandle, and a U.S. Geological Survey map shows the python could spread across one-third of the U.S. by the end of this century.


8. Termites

The formosan termite can quickly cause great structural damage.

Termites can cause extensive damage to a home in only a few months.

Termites cause an estimated $5 billion in damage each year in the U.S. The Formosan termite, an invasive species, is especially destructive; in a warm, moist climate, these termites can cause extensive damage in a matter of months. And that damage isn’t cheap to repair; according to Orkin, a homeowner who discovers termite damage will spend an average of $3,000 on repairs.


7. Zebra Mussels

Zebra mussels completely clogged this water intake pipe. Credit: InvasiveSpeciesInfo.gov

Zebra mussels completely clogged this water intake pipe. Credit: InvasiveSpeciesInfo.gov

First discovered in the Hudson River in 1991, this invasive species is expected to eventually spread to most North American waterways. These tiny mussels, which average about 1 inch in size, clog the water intake pipes of water treatment facilities, power plants, and other industries, costing millions in cleanup. The mussel also is a voracious consumer of nutrients and plankton that form the base of the aquatic food chain. In areas where they have been found, some species of fish have declined.

The federal and state governments have spent millions on education and inspection programs to prevent the spread of mussels to new waters, because these pests can take a great financial toll. For example, the U.S. Fish & Wildlife Service estimates that if the mussel invades the Columbia River, the giant hydroelectric plants there will spend up to $300 million each year dealing with the issue. Of course, those costs are passed on to consumers.


6. Emerald Ash Borer

The emerald ash borer threatens billions of ash trees in North America. Credit: USDA

The emerald ash borer threatens billions of ash trees in North America. Credit: USDA

This invasive species is a rather recent arrival, first discovered in Michigan in 2002, but it has already killed tens of millions of ash trees in the U.S. Billions more ash trees in North America are at risk. Despite efforts to contain this Asian beetle’s spread, it continues to expand its territory. One National Forest Service report estimates it would cost $10.7 billion to treat, remove and replace infected ash trees.


5. Imported Fire Ants

The fire ant's bite sends hundreds of people to emergency rooms each year.

The fire ant is particularly destructive to electrical equipment such as power transformers.

As with so many other invasive species, the imported fire ant arrived in the U.S. aboard a cargo ship. Since arriving almost 100 years, ago, the fire ant has flourished, spreading throughout the South. In addition to packing a painful sting that can be fatal to humans in some cases, these pests are highly destructive to the building blocks of modern civilization. They can damage or destroy power plant transformers, traffic signal boxes, air conditioners, and circuits and switching mechanisms. In the fields they can damage crops, and even injure or kill livestock. A 2006 Texas A&M study estimated fire ants cause some $6.7 billion in damages each year in the U.S.


4. Asian Carp

Asian carp, which have prolific leaping ability, are destroying the ecosystems in many rivers. Credit: Todd Davis/U.S. Army Corps of Engineers

Asian carp, which have prolific leaping ability, are severely damaging the ecosystems in many rivers. Credit: Todd Davis/U.S. Army Corps of Engineers

You’ve probably seen videos of this fish leaping out of some U.S. rivers by the dozens, slamming into unlucky boaters. Those clips are amusing to watch, but the Asian carp is no laughing matter in the U.S. Midwest, where this invasive species is ravishing river ecosystems. Originally imported to the U.S. from China to control algae growth in aquatic farms, the carp escaped into the Mississippi River and are steadily spreading through that river’s huge watershed. The Asian carp dominates every ecosystem it enters, reducing the populations of native fish, devouring vegetation other creatures eat and even lowering water quality.

The grave concern now is keeping the Asian carp out of the Great Lakes, where the fish could hurt the $7 billion annual fishing industry. To give you an idea how worried officials are about that possibility, the U.S. Army Corps of Engineers in 2014 proposed an $18 billion plan to prevent the invasive fish from reaching the Great Lakes.


3. Mosquitoes

Mosquitoes can spread deadly diseases, even in First World countries like the U.S.

Mosquitoes can spread deadly diseases, even in developed countries like the U.S.

Quick, what’s the deadliest creature in the world? If you guessed the shark, or poisonous snake, or lion, you’re not even close. The pesky little mosquito is the deadliest creature, resulting in more than 600,000 deaths each year due to malaria in the Third World. While that disease is not an issue in the United States, mosquito-borne illnesses such as West Nile virus can be deadly. According to the CDC, 286 people died of West Nile virus in the U.S. in 2012, and there were almost 5,700 total cases. In October 2015, public health officials warned residents in Southern California that mosquitoes there had been found carrying chikungunya and dengue and yellow fevers.


2. Deer

Around 200 people are killed each year in the United States in vehicle collisions involving deer.

There are around 1 million vehicle accidents involving deer each year in the U.S. © Tom Reichner

Because of conservation efforts in the 20th century, the deer population has exploded in America. If your vision of deer comes from seeing the film Bambi as a child, or gazing in wonder at several deer in your suburban yard one morning, you probably don’t realize why they are considered pests. But deer, both the white-tailed deer so common east of the Rockies and its western counterparts, are harmful in many ways. They eat or trample crops and fruit in orchards, and can destroy nurseries. The cost of that alone is estimated at $4.5 billion per year.

Then there is the issue of human interactions with deer, which often have deadly consequences. According to various sources, each year there are more than 1 million vehicle collisions involving deer, resulting in around 150 deaths and more than $3 billion in damage. And while deer don’t directly cause diseases such as Lyme disease, they do carry the deer ticks that spread illness.


1. Rats and Mice

Rats and mice cause an estimated $19 billion in damage each year in the U.S. © Michael Palmer

Rats and mice cause an estimated $19 billion in damage each year in the U.S. © Michael Palmer

The bane of homeowners everywhere, rats and mice cause a staggering amount of financial damage. One oft-cited study, while a bit dated (2005), puts the annual cost of rat-related damage in the U.S. at $19 billion. And that damage comes in ways the average homeowner setting mouse poison in the kitchen would little suspect. Rats and mice can be extremely destructive to nut and fruit trees. They contaminate livestock feed. Closer to home, they can chew the insulation off electrical wiring, causing house fires. And contact with rat droppings can cause diseases with exotic names (leptospirosis, salmonellosis, among others) you definitely don’t want.


Written by

The author is a longtime professional journalist who has interviewed everyone from presidential contenders to hall of fame athletes to rock 'n' roll legends while covering politics, sports, and other topics for both local and national publications and websites. His latest passions are history, geography and travel. He's traveled extensively around the United States seeking out the hidden wonders of the country.