Invasive species take many forms. They can be plants, mammals, birds, fish or invertebrates. But what they have in common is that they all contribute to millions of dollars in property damage in areas where they become established. And they often cause harm to the natural environment as well.

What are invasive species? Invasive species are any type of living organism that is not native to a local ecosystem but has been artificially introduced to the environment. This can happen through carelessness, such as zebra mussels entering the waters of the Great Lakes via cargo ship ballast water. Or even on purpose, when people release unwanted exotic pets or use non-native plants in landscaping. The Everglades in Florida is facing an environmental crisis from released Burmese pythons that are threatening its native American alligator species.

Some invasive species are highly localized and others more widespread. Here’s a list of some of the most invasive species in the U.S. -followed by ways that you can take action to help save local species.

Zebra Mussels (Dreissena polymorpha)

Zebra mussels are native to Eastern Europe and Western Russia. They were first discovered in the Great Lakes in 1988 after being accidentally introduced to the lakes via the discharge of contaminated cargo ship ballast water.

While zebra mussels are small – their shells are usually one-quarter to one-half inch long – they are damaging because they are voracious filter feeders and remove large amounts of plankton from the water. As an invasive species, this filter feeding upsets the entire ecosystem by competing with native species for their food source.

Along with the food chain impact, zebra mussels also clog power plant water intakes as well as damage boat hulls and engines. The damage is made worse because female zebra mussels can produce up to one million eggs each year. They now number in the billions in the Great Lakes and are responsible for $5 billion in control and repairs over the last 10 years.

To control zebra mussels, anyone living close to a port or have a boat in waters where they are found should be cautious of them. This means not keeping them as bait or in aquariums and keeping them off of boats and water-related equipment by washing with warm and soapy water.

Red Imported Fire Ant (Solenopsis invicta)

Red imported fire ants are native to South America. They were likely introduced in the U.S. between the mid-1930s and mid-1940s, possibly via ship’s ballast similar to zebra mussels. This invasive species is named for its painful, burning sting, and they have an immense financial impact with annual U.S. spending of $5 billion on control and medical treatment. They cause an additional $750 million in agricultural damage to crops and livestock each year, as well.

As part of a local ecosystem, red imported fire ants are here to stay. But the goal should be to suppress them as much as possible. Methods include using ant traps to draw in worker ants, which will take suppressants back to the queen ant – making her infertile or killing her. To directly treat fire ant mounds, pour two or three gallons of very hot water on the mound. This will kill around 60% of the mound’s population.

Wild Boar (Sus scrofia)

The Wild boar, also often called the feral hog, is a worldwide environmental scourge. They devastate large tracts of land by uprooting vegetation and causing excessive erosion. Additionally, they devour small animals including endangered species, and in coastal areas, they are a serious threat to marine turtles. Hogs were most likely introduced to the U.S. hundreds of years ago by Spanish explorers as livestock. More recently, European wild hogs, also called Russian boars, were introduced into Texas in the 1930s by ranchers and sportsmen for hunting. Escaped wild boars have developed large, feral populations – wreaking environmental havoc over the years.

The main control methods for wild boars are hunting and trapping. They are not classified as game animals, but regulations around hunting feral hogs vary from state to state. For example, both Texas and Florida require a hunting license for hunting on public lands, but Colorado doesn’t require any license. Unlike other game animals, most states that require a hunting license don’t have a set wild boar season and allow for year-round hunting.

Wild boars are considered very intelligent. While hunting, trapping, and snaring can help control their numbers – it’s unlikely that these methods will fully eradicate the species in a given range.

Eurasian Watermilfoil (Myriophyllum spicatum)

As its name indicates, Eurasian watermilfoil is native to Europe and Asia along with North Africa and was first found in the eastern U.S. in the early 1900s. It has since been introduced to 45 states with only Hawaii, Kansas, Wyoming, Idaho, and Nevada without reports of introduction.

This aquatic plant causes recreational, economic and environmental damage by outcompeting native plants, creating dense mats on the surface of water it has invaded, and impacting native animals by overtaking the more suitable native plant shelter, food, and nesting habitats.

Eurasian watermilfoil is spread through mediums such as water-related equipment i.e. boats, trailers, motors and anchors. Fragments of the plant can become tangled with the equipment and spread to new bodies of water where a single plant fragment can start a new population of the invasive species.

To combat this spread you should clean all water-related equipment of aquatic plants, drain water by removing drain plugs and keeping them out until the equipment has been transported, dispose of extra bait in the trash, and fully dry out any water-related equipment before using it another body of water.

To control an infestation, the two best methods are mechanically removing the plant by hand or with rakes or cutting blades and herbicides through two systemic herbicides (2,4-D and triclopyr) and two contact herbicides (endothall and diquat). There is current research around using native weevils as a form of biological control in Minnesota.

One caveat with Eurasian watermilfoil – it can be mistaken with beneficial native watermilfoils found in lakes and rivers.

Alligator Weed (Alternanthera philoxeroides)

Alligator weed is another aquatic plant invasive species native to South America. It was also most likely introduced via ballast water and was first reported in Alabama in 1897. Similar to Eurasian watermilfoil, alligator weed creates dense mats along shorelines and across the water surface that have an environmental impact by crowding out and killing native fish and plant species as well as impeding recreational water activities like boating, swimming and fishing.

This invader can be cut or grazed, but either method has to be extremely thorough because it will propagate from stem or root fragments. Herbicides are an option to eliminate alligator weed. Bispyribac is effective when mixed with water and sprayed onto, or injected into, alligator weed.