Fire ant head

The invasive fire ant has a mean bite and a nasty sting, and it's spreading across Louisiana. 

By air, land and sea, Louisiana has been invaded by a host of foreign critters that are wreaking havoc on farms, homes, wetlands and even our health.

Government agencies and conservation groups have spent decades and millions of dollars fighting invasive animals in Louisiana. But try as they might, many of these destructive bugs, fish and mammals are growing in numbers.

A few years ago, we teamed up with invasive species specialist Michael Massimi to highlight the 10 worst plant invaders in Louisiana – a list that included such leafy aggressors as bushkiller, giant salvinia, Chinese tallow and water hyacinth. 

We asked Massimi, who spent years battling invasives with the Barataria-Terrebonne National Estuary Program, to do the same for invasive animals. 

He focused his new rankings on overall effects to the state, with a touch of added weight for the newer arrivals.

“Better to raise the flag on a new species that still might be susceptible to control measures, rather than the ones that are old hat and thoroughly here to stay,” he said.

Turning back invasive animals isn’t the same as tackling their root-bound counterparts. While just about anybody can pull out a weed, it’s not advisable for everyone to go chasing after feral hogs or kicking over fire ant mounds.

Here, in ascending order, is Massimi’s list:

10. Tawny crazy ant

Crazy ants

Tawny crazy ants began spreading across Louisiana shortly after popping up in Texas about 20 years ago. 

The tawny crazy ant is the most recent in a series of ant invaders from South America. Likely stowaways in shipping containers, they appeared in Houston in 2002 and have since spread across swaths of Texas, Florida, Mississippi and south Louisiana, including an infestation at Audubon Zoo in New Orleans.

Crazy ants are easy to identify by their unusually hasty and erratic behavior. They crawl around like they’re, well, crazy.

Unlike the fire ant, another invasive pest (see below), crazy ants don’t sting and don’t have much of a bite. They do, however, tend to invade human spaces, sometimes overwhelming homes and yards. They get into electrical systems and cause short circuits and equipment failures. Crazy ants tend to dominate whatever area they’re in, pushing out other species, even casting bees from their hives. One positive: They tend to steal territory from fire ants, but many people who’ve had experience with both say they prefer fire ants because that species at least tends to keep to itself.

9. Lionfish


An invasive lionfish in Flowergarden Banks National Marine Sanctuary in the Gulf of Mexico. 

Resembling an explosion of striped fans, the lionfish is a popular aquarium centerpiece. But once introduced in U.S. waters – likely by owners who could no longer take care of it – the fish, a native of the Indian Ocean, has come to dominate warm coastal waters and coral reefs in the Atlantic Ocean and Gulf of Mexico.

Lionfish are fast breeders and voracious eaters. They gobble up native fish, turning once-vibrant reefs into lionfish wastelands. Native fish don’t see lionfish as predators, so they are very easy prey, especially the juveniles. Lionfish have predators in their home waters, but nothing in the Gulf is willing to eat them – that is, except people. They’re pretty delicious, but their spines, which pack a painful sting, make them a dangerous to catch.

Scientists say lionfish populations have not yet peaked in the Gulf, so the harm they’re causing to Flower Garden Banks National Marine Sanctuary and other coral-rich waters is likely still ramping up.

8. Apple snails

Apple snail and eggs

An apple snail lays a cluster of bright pink eggs. The snail is an invasive species that's causing trouble in Louisiana wetlands and farms.

The apple snail, another aquarium escapee, began spreading across Louisiana ponds, bayous and streams about 15 years ago. From South America and still quite popular in the aquarium trade, the snail tends to overpopulate waterways and eat up plants that provide habitat for native fish and other wildlife.

Slow as they are, the softball-sized gastropod has managed to ooze into at least 30 parishes, and has recently been causing problems in farms that produce two of the state’s favorite foods: rice and crawfish. When they hit a rice field, they hit it hard. Last year, the snails wiped out an entire 50-acre field. At crawfish farms, the snails clog traps, leaving little or no room for mudbugs.

Apple snails are edible but sometimes carry a parasite with an especially unappetizing name: rat lung worm.

7. Red imported fire ant

Fire ant raft

Fire ants drift in floodwaters from Hurricane Harvey near Pearland, Texas, in 2017. 

Few people forget their first meeting with fire ants. The aggressive insects both bite and sting anything that wanders into their territory. And their territory is growing.

Accidentally brought to Alabama by a ship from Argentina in the 1920s, the red, ground-dwelling ants have spread widely across the South and are now turning up as far away as California and Washington D.C. Their high reproductive rates, lack of natural predators and ability to join together to form rafts during flooding have allowed the fire ant to displace some native ant populations.

Recent research has shown rising seas and increased flooding are triggering a new breed of fire ant that has a bigger head for biting and a much larger venom sac to make each sting more painful.

6. Roseau scale

Roseau scale

Rodrigo Diaz, a Louisiana State University biologist, uses a pencil to point to the tiny scale insect blamed for widespread roseau cane die-offs in south Louisiana.

This tiny insect from Japan and China has only been in Louisiana for a few years, but it’s already decimated vast stands of roseau cane, a wetland plant considered one of the state’s best natural defenses against land loss and rising seas.

The scale looks harmless enough, little more than a pale-colored nub tucked into the cane’s leaves. But the scale is sucking roseau dry and weakening the grip of its land-building, land-elevating roots. Hard-hit roseau marshes in south Plaquemines Parish, where the Mississippi River meets the Gulf, have been converted to open water in a matter of months.

Battling the scale might require help from another invader. The invasive European strain of roseau cane, which is taking over wetlands on the East Coast and Great Lakes region, is highly resistant to the scale. Already making inroads in Louisiana, Euro roseau could end up replacing local varieties. That might be good for easing the state’s land loss crisis, but it could require expensive control efforts to keep the plant in check.

5. Feral hog

Feral hog with trapper

Trapper John Schmidt wrestles a feral hog as he transfers it from a trap to a kennel in the woods in Algiers on Wednesday, Nov 20, 2013. 

Descendants of domestic pigs and wild Eurasian boars, feral hogs devour sugar cane, sorghum and rice, causing almost $80 million in agricultural losses each year in Louisiana. They also rip apart coastal marshes, contributing to erosion and land loss.

There are now more of these hairy, tusked pigs in Louisiana than the human populations of Baton Rouge and New Orleans combined. Feral hogs had been mostly a problem in the South, but now they’re causing trouble farther north in such states as Vermont and Washington.

Louisiana hunters kill more than 150,000 feral hogs each year, but it’s not nearly enough to limit the species' growth. Almost a half million of the animals would need to be shot, poisoned or trapped each year just to maintain a static population.

State researchers recently found that the hog’s appetite ranges more wider than initially thought. Inventories of hog stomachs revealed the remnants of shorebird and alligator eggs, turkey babies, rabbits, snakes, young trees and imperiled species of turtles and salamanders.

4. Asian carp

Asian carp

In this June 13, 2012 file photo, Asian carp jolted by an electric current from a research boat jump from the Illinois River near Havana, Ill.  

Asian carp were brought to the United States in the 1970s to control algae and plant growth in catfish ponds and other aquaculture operations. They did an amazing job, but now the their escaped descendants are applying that same work ethic to the Mississippi River Basin, stripping away aquatic vegetation and plankton on which native fish depend.

They were almost designed to cause problems. Carp are highly adaptable, aggressive and grow quickly, sometimes reaching 100 pounds. They’re both voracious eaters and inefficient digesters, which means they have to eat exceedingly large amounts of food. 

Carp also pose a risk to boaters. When spooked, carp tend to leap out of the water, sometimes hitting people and causing injuries and even a few deaths.

Carp are pretty tasty, but they’re loaded with bones. The state and local chefs have tried promoting carp, rebranded as silverfin, in highly processed, boneless products, but carp cakes have yet to get much real estate in supermarket freezers.

3. Formosan termite

Termite swarm

Termites swarm in New Orleans' Uptown neighborhood in May 2016. 

These little homewreckers first popped up in New Orleans and other U.S. ports after World War II, likely via infested shipping crates.

Known to swarm in Louisiana in late spring, Formosan termites cause millions of dollars worth of damage each year in New Orleans, where they’ve been the kiss of death for many historic buildings. They also attack healthy trees and seem to have a special fondness for pecan, citrus and oak trees.

Formosan termites easily push out native termite populations. In their place, Formosan termites build much bigger colonies that can stretch more than 300 feet underground and contain 4 million hungry bugs.

Mostly confined to the parishes south of Interstate 10, Formosan termites are spreading, usually thanks to unwitting humans. They’re now munching buildings in Beauregard, Vernon and Sabine parishes and have been spotted as far north as Ouachita Parish.

2. Asian tiger mosquito

Tiger mosquito

An Asian tiger mosquito draws blood from a finger. The insect can transmit West Nile virus and other several other diseases. 

This tiger-striped blood sucker is the invasive that likely poses the greatest risk to human health. The Asian tiger mosquito can transmit numerous diseases, including Dengue, Zika and West Nile virus. It can also harm pets, most notably as a prime spreader of parasitic heartworms in dogs.

The tiger mosquito first appeared in the U.S. in 1985 when a shipment of infested tires were offloaded in Houston. Now they’re in at least 40 states.

Unlike many other Louisiana mosquitoes, the tiger mosquito feeds during the day and prefers human beings and other mammals over other species. It’s a bit more aggressive than the local bugs, but it’s also relatively weak, making it a low-level flier. That means their bites tend to target the ankles and legs.

Scientists don’t yet have a good control method for tiger mosquitos, so the best defense is reducing the number of outdoor containers that can hold water. The mosquitoes can breed in tires, buckets, bird feeders, clogged gutters, pet food dishes, toys – just about anything that holds water, even a small amount.

1. Nutria


Nutria, also known as "swamp rats," have been eating away coastal marshes since they were brought to Louisiana from South America in the 1930s.

Topping our list is the large, semi-aquatic rodent that’s literally eating away the state. Louisiana wildlife managers estimate nutria have contributed to the loss of at least 40 square miles of land over the past two decades.

In the 1930s, the Louisiana fur industry imported nutria from South America as a new source of pelts for coats and hats. Some nutria escaped, and many more were released after the fur market tanked. They spread fast across the South and are now destroying wetlands in Oregon and California.

Louisiana recently upped its $5 nutria tail bounty to $6. Despite the boost, only 246,000 tails were collected by hunters last year. That’s far fewer than the record of 446,000 a decade ago. Hunters would have to kill about that many each year just to hold the line against the nutria's explosive growth.

The state and nonprofit groups spent a good chunk of money over the past 20 years trying to revive interest in nutria furs and make nutria meat a trendy menu item in New Orleans restaurants. Both efforts have yet to catch on.

. . . . . . .

There are plenty more invasive species causing trouble in Louisiana. Here are a few of Massimi’s dishonorable mentions:

  • Spotted jellyfish
  • Asian tiger shrimp
  • Rio Grande cichlid
  • Tilapia
  • Zebra mussel
  • Asian clam
  • Brown anole
  • Cuban treefrog
  • Asian citrus psyllid
  • Citrus canker
  • Emerald ash borer
  • House sparrow
  • European starling
  • Africanized honeybees
  • Feral cats

Tristan Baurick:; on Twitter: @tristanbaurick.