A beginner’s guide to invasive species

Antonius R. Chess Jr., Cornell Cooperative Extension of Yates County


Invasive species have become a serious issue across the United States. Invasive species are organisms that are not native to an ecosystem and spread quickly. Their characteristics enable them to outcompete native species in an ecosystem, reducing species diversity. According to the National Wildlife Federation (NWF), there are over 4,000 invasive species in the United States and 42% of threatened or endangered species are at risk as a result. Human health and economics are also impacted by invasive species.


Before we can prevent the spread of an invasive species, we must understand what causes them to spread and the impacts. According to the NWF, human activity is the main cause of invasive species spreading to new environments:

● Commercial and recreational ships carrying aquatic organisms in the ballast water

● Transporting wood containing eggs or larvae. Even wooden pallets and crates on shipping goods carry eggs or larvae.

● People buying ornamental plants

● Climate change affecting an ecosystem’s ability to accommodate new species

When an invasive species enters a new environment, there may not be natural predators or controls to naturally mitigate the spread. According to the Fish and Wildlife Service (FWS) the potential impacts of an invasive on an ecosystem include:

● Preying on native species

● Outcompeting the native species

● Destroying or replacing other species food source

● Spreading disease

● Increasing soil erosion

● Degrading habitat

Invasive species also impact the economy and public health. The FWS lists off ways they impact us:

● Clog waterways for boating, fishing, and other recreational activities

● Spread to agricultural settings and invade fields, some posing risks to farm animals and reducing crop yields

● Damaging power plants and industrial water systems

● Reduce revenue to natural resource-based businesses

● Can be poisonous to humans (e.g., giant hogweed)

● Carrying diseases

Some invasive species causing issues in NY include spotted lanternfly, starry stonewort, black and pale swallow-wort, and hydrilla.


Native to Asia, the Spotted Lantern Fly (SLF) is an invasive insect that made its way to the United States in 2014. They are approximately one inch in length and one-half inch wide; grey and black forewings with contrasting patches of red and black on the hindwings and a large abdomen. According to Penn State Extension, SLF feeds on sap from over 70 different plant species. As SLF feeds, it releases a sugary substance called honeydew which causes mold to grow on the plant, interfering with photosynthesis. According to the Department of Environmental Conservation (DEC), SLF spreads primarily by laying eggs on vehicles, firewood, stones, and other transportable outdoor goods.

Spotted Lanternfly nymphs and adults.

To manage the spread of SLF, quarantines have been implemented restricting the movement of goods from any county that shows evidence of reproducing colonies. The Department of Agriculture and Markets (DAM) conducts inspections of shipments and trapping surveys in high-risk areas. The DEC established prevention zones for early monitoring in near counties.

To help prevent the spread of SLF, inspect your vehicles and equipment when traveling. If you think you have found SLF email spottedlanternfly@agriculture.ny.gov with the location, nearby roads, and/or GPS coordinates.


Starry stonewort (SSW) is native to Europe and Western Asia and grows submerged in lakes, ponds, and slow rivers. To identify SSW, look for whorls of 4-6 branchlets. Bulbils produced at the nodes in mid-late summer are white and star shaped. It spreads by fragments attaching to water vessels, trailers, and anchors. According to the DEC, SSW has spread to 14 counties in New York.

Starry stonewort grows along a lake bottom.

The threat being it forms dense mats in lakes that can:

● Reduce biodiversity of aquatic plants by outcompeting them

● Impede fish movement and spawning activity

● Reduce fish habitat

● Disrupt water flow and chemistry

● Clog waterways

Chemical methods such as the use of herbicides and mechanical methods such as pulling and harvesting, are used to help manage the spread. Additionally, watercraft stewards educate watercraft users about aquatic invasive species and inspect watercrafts for vegetation to help prevent their spread.

To help prevent the spread of SSW, it is important to inspect, clean, drain and dry your watercraft, along with your equipment, after every use. If found, report to your local DEC office or cooperative extension and dispose of the sample in a garbage.


Also known as dog-strangling vine, swallow-wort is a perennial climbing vine that grows in a variety of environmental conditions. According to Cornell Cooperative Extension (CCE), the plant came to the United States as an ornamental plant for horticultural purposes. They emerge in the spring, flower in the early summer, and produce seeds in the late summer. The DEC states they are capable of self-fertilization and can produce 1000-2000 seeds per year that spread via wind. Herbivores tend to avoid swallow-wort as it is difficult to navigate through.

Flowering black swallow-wort (left) and pale swallow-wort (right). The flowers have spread across the northeast U.S. and southeast Canada and are appearing further west.

Swallow-wort infestations can lead to loss of habitat, food sources, biodiversity, and damages microbial communities. Pale swallow-wort, which is most common in NY, negatively impacts the monarch butterfly by outcompeting and displacing milkweed and swallow-wort is not a viable alternative for monarchs to lay eggs on. Management practices include mechanical, chemical, and biological control is being researched. Mechanical controls include harvesting and disposing, as well as mowing to prevent seed formation. Chemical herbicides are used on cut stems. Hypena opulenta, a moth that has recently been accepted as biological control for swallow-wort in the U.S., feeds on leaves, inhibiting photosynthesis.


This submersed, perennial plant was first introduced to the U.S. as an aquarium plant from the Indian subcontinent, Sri Lanka. In the U.S. it can grow in freshwater lakes, ponds, rivers, impoundments, and canals.

Outbreaks of hydrilla are being managed in Tompkins County.

Hydrilla propagates by stem fragmentation. Fragments stuck to watercrafts allows for the spread and growth of buds and tubers in new environments. Hydrilla can grow in deep waters, with little to no competition from other plants. With the lack of competition, they grow in dense mats and as high as 25 feet, blocking sunlight from other plants. This reduces available growth space for other plants, causing a decrease in native vegetation, open water, waterfowl feeding areas, and fish spawning sites. Hydrilla also obstructs boaters and swimmers, can stratify the water column, and decrease the level of dissolved oxygen.

Hydrilla has pointed bright green leaves that grow in whorls of four or more, and are typically serrated or toothed. They have thin stalks and a single floating white flower. Watercraft steward programs help monitor boats for vegetation, including hydrilla but it is important that you inspect, clean, drain and dry your watercraft, along with your equipment, after every use.


 Prevention is the best way to stop the spread of all invasive species so let's work together! Join the fight against invasive species by downloading the app “iMapInvasives,” and post your findings on a shared database.

Consider joining the Partnerships for Regional Invasive Species Management (PRISMs) e-mail list through the website http://nyis.info/prisms/ to get invasive species information and updates and/or volunteer with the Finger Lakes PRISM (http://fingerlakesinvasives.org/). For other opportunities, reach out to your local Cornell Cooperative Extension office.