5 Invasive Species That Are Wreaking Havoc In California

California is the most ecologically diverse state in the country. It has more native life to its name than any other place in the nation, being home to over 40,000 unique plant and animal species, including nearly a quarter of all the plant varieties in North America. This astounding level of biodiversity is a product of California's one-of-a-kind climate. Crossing nearly 10 lines of latitude, California features many of the main types of climate regions, including temperate, desert, and highland climates, not to mention over 800 miles of coastline where marine life thrives. Many of California's species are exclusive to the state, and unfortunately, they have been increasingly threatened by outsiders.

Human activities have introduced many non-native species to California, several of which have become widespread within the state. Invasive species like these are one of the leading causes of animals becoming endangered. They can disrupt the food chain, take over precious resources, and spread diseases amongst both wildlife and human beings. Removing invasive species presents a massive challenge, as many of them have been spreading for decades, and new ones are constantly showing up. Here are five species that are causing some of the most significant problems for California right now, and what, if anything, can be done about them.

The American bullfrog (Lithobates catesbeianus) is the largest North American frog species. It is endemic to the eastern United States, but they did not appear west of the Great Plains until the early 20th century, when large numbers of bullfrogs were introduced to the western states for the purposes of food and pest control. Bullfrogs have since continued to invade non-native lands by escaping from farms, laboratories, and pet owners, and they can now be found in most states, along with parts of Europe, Asia, and South America.

Bullfrogs are an especially aggressive invasive species because of their size, voracious appetites, and high reproductive rates. These hungry creatures will eat almost anything, feeding on insects, rodents, reptiles, birds, and most problematically, other frog species. American bullfrogs outweigh any frogs endemic to California, and they rob native species of much of their food supply.

American bullfrogs also carry a skin disease that's deadly to native frogs. Known as chytrid fungus, it is harmless to the bullfrog but can kill other types of frogs. One species that has been particularly threatened by the American bullfrog is the native Californian mountain yellow-legged frog, which is especially affected by chytrid fungus. Once the most common frog in the Sierra Nevadas, the mountain yellow-legged frog has now disappeared from over 90% of its former territory, and it's predicted to go extinct within a few decades.

As their name suggests, Argentine ants (Linepithema humile) don't belong anywhere near California. They are originally from central South America, found in Argentina, Paraguay, Uruguay, Bolivia, and Brazil. It is widely suspected that Argentine ants first entered the United States in the late 1800s, arriving in New Orleans via shipments of coffee from Brazil. By 1907, the species was found in California, and it is now widespread throughout the Golden State, mainly along the coastline.

Argentine ants create supercolonies that can host a trillion individuals with multiple queens. These supercolonies are the largest collectives of multicellular organisms on Earth, and they are invading homes all over California. UCSD reports that Argentine ants are responsible for more calls to exterminators than any other pest in the state, and they are widely considered to be the most successful invasive species in California. Argentine ants are extremely aggressive, and they will group together to kill larger types of ants. This attitude has turned the invasive species into the most common ant in California.

Argentine ants wreak havoc on agriculture because they have a symbiotic relationship with aphids. Aphids, and a number of other common garden pests for that matter, secrete a sugary liquid called honeydew, which Argentine ants love to feed on. In exchange, the ants protect aphids from predators, allowing aphids to flourish and destroy many crops. While exterminators are experienced in tending to these pests, the utter dominance that Argentine ants have exerted over California means that fully eliminating their threat is likely impossible.

The European green crab (Carcinus maenas) is one of California's most troublesome marine invasive species. Native to the coastal waters of Europe and North Africa, they were accidentally brought to North America in the 1800s via the ballast water of trade ships and began taking root along the East Coast. In the late 1980s, green crabs were discovered in San Francisco Bay, and they're now found from California all the way north to Alaska.

European green crabs prey on fellow shellfish, including native clams, mussels, and other crabs, just some of the animals that live in intertidal zones. Despite being only two to four inches in width, these crabs have big appetites. A single European green crab can eat as many as 40 shellfish in a single day, leaving little food for others. Omnivorous, they also eat seagrass, which has historically provided shelter for vulnerable young fish. One creature especially harmed by green crabs is the Dungeness crab, a species exclusive to the Pacific coast of the United States, which has seen much of its food supply consumed by the invaders.

By decimating local fish populations, green crabs cost the fishing industry roughly $20 million per year, according to research conducted by Abt Associates Inc. In the 2010s, efforts were made to eliminate green crabs in the San Francisco Bay Area. The plan backfired because it turns out that, in addition to eating other crabs, green crabs practice cannibalism. When fishermen began catching them, the crabs simply stopped eating each other, allowing their population to boom. Unfortunately, it seems they are here for good.

Mute swans (Cygnus olor) have long held a lofty position in Western culture due to their association with British royalty. Since the 12th century, these majestic birds have been considered great status symbols in Europe, with nobles often keeping them as pets (not to mention eating them). To this day, all unmarked swans in the U.K. are technically property of the Crown. During the Victorian era, many wealthy Americans had mute swans imported from Europe so that they too could display them as status symbols. Unfortunately, this led to some swans escaping from zoos and estates, and once they entered the wild, things got out of hand fast.

Despite their serene image, mute swans are aggressive, and they will not hesitate to attack anything they perceive as a threat. These massive birds have attacked humans and even killed dogs. Weighing in around 30 pounds each, mute swans have huge appetites, and they are rapidly decimating marshlands, leaving little vegetation for native fish and other waterfowl to eat.

They also reproduce at an aggressive rate, so the population could grow and spread rapidly. This would be a serious threat to California's two native swan species, the tundra swan and trumpeter swan, with the tundra being especially vulnerable, as it is much smaller than a mute swan. Along with other waterfowl, fish, and crustaceans, these native swans are losing food to the voracious invaders.

Ice plant (Carpobrotus edulis) is arguably California's most notorious vegetative invader. It grows all along the coastline, forming a thick green carpet over cliffs and dunes. The plants flourish because California's coastal climate is very close to that of their native home in South Africa. Ice plant was originally brought to the Golden State in the early 1900s, when it was planted alongside railroad tracks to stabilize the soil. It was later used for the same purpose in building highways, but once it entered the California ecosystem, it began spreading out of control.

Ice plant grows close to the ground, its branches forming a tightly woven mat of vegetation. It spreads rapidly, taking land and nutrients away from native plants. Although it was imported to stabilize railroads and highways, it turns out that ice plant is actually very bad at soil stabilization because as it grows, its leaves become so heavy that they can cause landslides.

Numerous organizations within California have worked to remove ice plants from the state's beaches, and local students often participate in clearing efforts as a form of community service and environmental education. Beaches where ice plants have been eliminated have been able to support greater plant diversity, which welcomes a wider array of wildlife. However, ice plants are hard to kill completely. A small piece of stem left on the beach can regrow a whole plant, and with how widespread ice plant has become in the state, it's likely there for good as well.