Due to the diversity of terrain, Arizona is home to a variety of plants and animals. However, many invasive species threaten and disrupt the natural balance of the local ecosystem by displacing or out-competing native species, monopolizing nutrients and water resources, and more. Invasive species in Arizona include plants, birds, fish, insects, and amphibians.
Many of these invasive species were introduced to Arizona from other countries or states. Because the invasive species are causing an imbalance in the local ecosystem, it is imperative that we find a way to control the spread of these species. However, the management and prevention of invasive species is an ongoing challenge in Arizona and requires the cooperation and efforts of government agencies, conservation organizations, and even the individuals who live there.
Tamarisk is a shrub or small tree that is considered an invasive species in Arizona. This plant is evergreen and grows from 3.3 to 59.1 feet in height. Their preferred soil is saline but can also tolerate alkaline soil. You can recognize this plant by its slender branches and gray-green foliage. The leaves of the tamarisk are scale-like and can range from 1/20 inches to 1/10 inches long. The tamarisk is a flowering plant and flowers appear on the plant in dense masses.
The tamarisk plant, which is also commonly referred to as the salt cedar, is originally from Asia and was introduced to the area as an ornamental and windbreak in the 1800s. There are over 1 million acres of tamarisk in the southwestern stream banks. The tamarisk is considered an invasive species because it lowers stream flows and water tables. They also increase soil salinity and displace native species and wildlife habitats.
Forest rangers in Grand Canyon National Park have been working on getting rid of tamarisk in the environment. This is a labor-intensive task that involves the chemical and physical removal of the plant.
Knapweed (Diffuse, Spotted, and Russian)
Knapweed is a weed plant that is considered to be an invasive species in Arizona. This plant has leaves that are divided into elongated lobes near the lower part of the plant. Some species have spiny leaves. The flowers that you can see are actually pseudanthium inflorescences which come in different colors – blues, reds, yellow, white, and more. Each pseudanthium sits on top of a cluster of scaly bracts.
Knapweed is originally from the Mediterranean and was only introduced within the last 100 years. Three varieties of knapweed can be found in 10 states across millions of acres. The knapweed is considered an invasive species as it threatens pastures and rangelands. They also out-compete native vegetation — a truly invasive species. The plant disturbs the soil, draining it of vital nutrients. The wildlife organizations in Arizona have been working to control the invasive plant to allow native plants to thrive.
Fountain grass (aka crimson fountain grass) is a bunching grass that is considered an invasive species in Arizona. It is a clump-forming grass that has deep roots and short rhizomes — perfect to form new plants. Their leaves are green, round, thin, and tough. They erect purplish-white stems that support bristly flower heads that are colorful (generally purple-brown).
Fountain grass is native to Africa and was introduced as a landscaping plant. Now you can find them on roadsides, washes, and canyons in Southern Arizona. Fountain grass is considered invasive as it crowds out other species and monopolizes nutrient and water resources. Not only that, these plants are extremely difficult to eradicate. Killing the weed with chemicals is challenging because you may need to respray the plant 2 to 3 times before it ceases to grow back.
Buffelgrass is a species of grass that is considered to be invasive to Arizona. It can grow from 10 to 50 inches in height and have linear leaves that are 1 to 10 inches long. The plant produces flowers that are 0.8 inches to 5.5 inches in length and 0.4 to 1 inch in width.
Buffelgrass originated from Africa and was introduced for cattle forage. The wind dispersed the seeds, which grew quickly on roadsides, vacant lots, alleys, and deserts. Buffelgrass is an extremely hardy plant that is considered an invasive species. It produces dense colonies that exclude other species and monopolize nutrient and water resources. Like the fountain grass, Buffelgrass is challenging to eradicate.
The only way to kill buffelgrass with herbicide is to use broad-spectrum herbicides that will also affect non-invasive species. This is not ideal, as you will likely kill off native species while removing buffelgrass.
Yellow Star Thistle
Yellow star thistle is a species of thorny plant that is considered an invasive species in Arizona. When the plant is flowering, the stem can grow up to around 1.5 feet in height. The leaves that grow at the base are lobed and between 2 to 3 inches long. The leaves that grow on the stem are unlobed and smaller. The stem produces many spinous flower heads with striking yellow coloring when flowering.
The yellow star thistle is native to the Mediterranean Basin region and was introduced (unintentionally) to California around 1850. Now the plant extends over 15-22 million acres in California and throughout Arizona. The yellow star thistle is considered an invasive species because it can cause fatal chewing disease in horses. The dense plant displaces native vegetation and multiplies rapidly which increases the likelihood of horses eating it.
Fortunately, the yellow star thistle is not incredibly difficult to remove. You can dig it up or even hand-pull the plant as long as you remove the roots.
This non-native tree has become invasive in some regions of Arizona. It is native to Central America and Mexico and was introduced to Arizona and other parts of the United States as an ornamental plant. Sweet acacia can multiply very fast and can reach heights of up to 20 feet. Its leaves are small and feathery, and its branches are usually laced with thorns. The tree produces small yellow flowers and seed pods that contain seeds that are spread by the wind, water, or animals.
In Arizona, sweet acacia is considered a problem in river bank areas and other moist habitats, where it can outcompete other native plant species and alter the structure and function of the ecosystem. It can form dense thickets, making it difficult for other plants to get enough light and nutrients. Ways to stop the spread of the sweet acacia tree include removal or chemical treatment with herbicides. The use of biological control agents such as insects is also being explored.
The common carp is a freshwater bottom feeding fish that is considered an invasive species in Arizona. It is a large, heavy-bodied fish that can weigh from 4.4 to 30.9 lbs. These fish have a dark gold sheen and large scales making them shiny in appearance. They also have two pairs of barbels. These fish are tolerant of most conditions but do prefer large bodies of slow or still water.
Because these fish are omnivorous, they feed on a wide range of species. The common carp is native to Eurasia and was introduced as a food fish in 1872. Now they can be found in the Grand Canyon and Lake Mead. The common carp is considered an invasive species because they out-compete native fish and increase water turbidity. The fish stirs up lots of mud in the water and eats lots of the nutrients and plant material in the water, causing issues for the other fish species.
Carp removal efforts can involve the use of nets or traps. This can be very labor intensive but is very effective in reducing carp populations in specific areas.
The northern crayfish is a species of crayfish that is native to the eastern United States and southeast Canada. The crayfish was introduced over 40 years ago to control aquatic weeds and as live bait for sport fish. They like to habitat still or slow-moving bodies of water within Santa Cruz, Salt, Gila, and Little Colorado Watersheds. These crayfish are reddish brown or green and have pincers that are green or blue-green. The pincers have orange tips, and adult crayfish have whitish knobs on their pincers.
The northern crayfish population has exploded in Arizona and has affected a number of native species. Because of the damage that they cause, they are considered an invasive species in Arizona. Their diet can consist of snails, tadpoles, native fish eggs, frogs, and small turtles. Not only do they affect the ecosystem in Arizona with their diet, but they also disturb stream bottoms, making the clear water muddy.
Bullfrogs are a frog species native to the eastern and central United States. They are giant frogs, with adult males reaching up to 8 inches long and females up to 6 inches. They are usually green or brown with white spots or blotches on their skin. They also have large eardrums on the sides of their heads. In the early 1900s, they were introduced to Arizona for use in the food and pet trades, and have since spread to many areas.
Bullfrogs are a threat to native wildlife in Arizona, as they are predators that eat a wide variety of prey, including other native amphibians, fish, invertebrates, and even birds. They also compete with native species for resources and can transmit diseases to other animals, and carry pathogens that other native frogs cannot fight off. They do not have many natural predators in Arizona. So, since bullfrogs breed prolifically they often outcompete the breeding of native frogs, laying up to 20,000 eggs at a time. Removing the bullfrogs from their habitats and limiting their importation for the pet and food trades are just some of the ways that Arizona is trying to control this invasive species.
Originally coming from Ukraine and Russia, Quagga mussels were first found in Arizona in 2007. They have since established populations in many waterways including Lake Mead, Lake Pleasant, and the Colorado River. The quagga mussel is a small freshwater mollusk that is typically ¼ to 1 inch in size, although it can grow up to 2 inches big. They have a very distinct pattern of dark and light stripes on their shell which are beige or light brown in color.
Quagga mussels are considered a threat to native populations and aquatic ecosystems because they can easily outcompete other species for food and habitats. They are filter feeders and require a large amount of plankton, which can reduce the food available for other aquatic wildlife. In addition, they are able to reproduce more than once a year and are capable of producing up to one million eggs annually.
Efforts to control quagga mussels in Arizona have included public education campaigns to prevent the spread of the species through recreational activities such as boating and swimming. However, due to their microscopic eggs and widespread distribution, the mussel remains a significant threat to aquatic ecosystems in Arizona.
The brown-headed cowbird is a medium-sized bird that is native to the Great Plains and measures about 7 to 8 inches long, weighing around 1.5 to 2 ounces. They have a stocky build and a short thick bill that is adapted for cracking open seeds. The males have glossy black feathers and a brown head with distinctive purple or green feathers on the back. Females, on the other hand, are a dull gray-brown color.
Cowbirds are known to lay their eggs in another bird’s nests, known as “brood parasitism.” The cowbird’s eggs are often larger than their host bird’s eggs and the chick will usually outcompete the host’s chick for food. Often the cowbird chick will push the other eggs out of the nest. Cowbirds are a huge threat to native species as they can reduce the reproductive success of the host birds, especially songbirds.
There have been efforts in Arizona to control cowbird populations, including monitoring programs to track the spread of the species and the removal of cowbird eggs from host bird nests.
The Tamarisk Beetle is a small oval-shaped beetle that is around a quarter of an inch in length. The adults are a metallic green color and have flat bodies, small heads, and long, thin antennae.
The beetle is an imported species used to control the invasive Tamarisk plant in the Western United States including Arizona. Originally from China, this beetle has proven to be very successful in controlling the spread of Tamarisk. However, there are concerns that the beetle has started feeding on other native plant species, which could negatively affect the ecosystem.
Since being introduced to Utah in 2000, the tamarisk beetle population has bloomed and is now considered to be beyond the point of being controlled by humans.
European starlings were brought to North America around 1890 and released in Central Park as part of an attempt to introduce all the birds mentioned in Shakespeare. They are medium-sized birds that are around 8 inches in length with black plumage and white speckles. Their beak is black in the winter and yellow during the summer.
In Arizona, starlings are considered an invasive species because they compete with native birds for food and nesting sites. Starlings are very aggressive birds that destroy the eggs and kill nestlings of many native species. They are also known to damage crops and gardens as they have a huge appetite and eat large amounts of fruit and seeds.
Starlings can adapt easily to any habitat, which allows them to spread rapidly throughout the country, including Arizona. They can form large flocks which can number in the thousands and can be very noisy and disruptive.
Red-eared sliders are a species of turtle native to Mississippi, Tennessee, and Cumberland Valleys of the U.S., as well as northern Mexico. They have become invasive in Arizona, and in many other parts of the world due to their popularity as pets. Many of these pets will often escape or get released into the wild. They are medium-sized turtles with very distinctive markings on their face and shells. The most recognizable feature is the red or orange stripe behind the turtle’s eyes, which gives them their name.
Red-eared sliders are known for out-competing native species and can alter aquatic ecosystems. They have been observed to consume large amounts of aquatic vegetation affecting the quality of the waterways they inhabit. As well as this, their burrowing behavior can destabilize shorelines and cause damage to infrastructure.
There have been strong efforts to manage red-eared sliders, including trapping and removal programs, and encouragement to the public to not release their pet turtles into the wild. However, due to the high breeding rates and widespread distribution, these turtles remain a significant threat to Arizona’s native wildlife and ecosystems.
Summary of 14 Invasive Species in Arizona
Here’s a recap of the invasive species present in the state of Arizona that we took a close look at:
|Number||Species Name||Origin||Reason It Is Invasive|
|1||Tamarisk (Saltcedar)||Asia||Lowers stream flows and water tables, increases soil salinity, displaces native species and wildlife habitats|
|2||Knapweed (Diffuse, Spotted, and Russian)||Mediterranean||Threatens pastures and rangelands, outcompetes native vegetation|
|3||Fountain Grass||Africa||Crowds out other species and monopolizes nutrient and water resources|
|4||Buffelgrass||Africa||Creates colonies that exclude other species, monopolizes nutrient and water resources|
|5||Yellow Star Thistle||Mediterranean Basin||Can cause fatal chewing disease in horses, displaces native vegetation, multiplies rapidly|
|6||Sweet Acacia||Central America and Mexico||Outcompetes native plant species, alters structure and function of the ecosystem|
|7||Common Carp||Eurasia||Outcompetes native fish, increases water turbidity|
|8||Northern Crayfish||Eastern United States and southeast Canada||Affects native species and ecosystem with its diet, disturbs stream bottoms|
|9||Bullfrogs||Eastern and central U.S.||Eat a wide variety of prey, compete with native species for resources and transmit diseases to other animals|
|10||Quagga Mussels||Ukraine and Russia||Outcompete other species for food and habitats, reduce food available for other wildlife|
|11||Cowbirds||Great Plains||Reduce reproductive success of other birds, especially songbirds|
|12||Tamarisk Beetle||China||Feeds on native plant species, which affects ecosystem|
|13||Starlings||Europe||Compete with native birds for food and nesting sites, destroy eggs and kill nestlings of native species, damage crops and gardens|
|14||Red-Eared Sliders||Mississippi, Tennessee, and Cumberland Valleys of the U.S., northern Mexico||Outcompete native species, alter aquatic ecosystems, destabilize shorelines, damage infrastructure|
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