ANNAPOLIS, MD (January 1, 2016) – We've never seen an invasive species quite like this one before. The waterwheel (Aldrovanda vesiculosa L.) is an herbaceous carnivorous aquatic plant closely related to sundews (Drosera spp.) and Venus flytraps (Dionaea muscipula). It catches animal prey through an active trap mechanism, much like the Venus flytrap, by snapping its mouth-like leaves shut when they are triggered. Found at the tips of the leaves, traps may number as many as 200 per plant. Estimates by researchers are that 80% of the traps may contain prey at any given time. These traps catch untold numbers of insects and other animals, which gives this invasive species a new twist — not only can it invade wetlands, but it also impacts habitats by predation. This predation gives scientists great concern about waterwheel's effect on food webs and its impacts on rare invertebrate species.

Waterwheel is unique among our invaders because it is an IUCN Red List and Globally endangered species. Aldrovanda is globally rare and declining where it is native in Eurasia and Africa. In North America it is known to be introduced and locally abundant only in New Jersey, New York, and Virginia. The introduced populations in North America rival or surpass in size the largest populations in the species' entire natural range. A single pond in New York is estimated to have a population of several million individuals. Thankfully, waterwheel has yet to be documented in Maryland.

MISC has selected waterwheel as the January Invader of the Month to raise awareness of this species during next growing season.

Waterwheel is a rootless, floating aquatic plant. It has jointed leafy stems, with whorls of six to nine leaves less than half an inch long. Each leaf has a kidney-shaped hinged blade with bristles on each side, which snaps shut around any insect unlucky enough to land on the blade. The tiny greenish-white flowers are solitary, in the axils, with five petals and stamens. Fruits are also five-parted; they are small round capsules, with glossy black seeds. Superficially, waterwheel is very similar to Hydrilla (Hydrilla verticillata), a rooted, rhizomatous aquatic, in overall appearance and abundance. Care must be taken to distinguish the two (see Hydrilla pictures from the Invader of the Month – June 2009).

Waterwheel is currently known to occupy manmade wetland habitats, blackwater seeps, and pools of acidic and tannic water. In optimal conditions it can grow at nearly exponential rates, doubling its mass in 13-15 days, growing 9 mm of new stem and one new whorl of carnivorous leaves per day. A single individual can produce 20-30 new shoots of leaves per year.

Waterwheel can spread by seeds, the transportation of leaf material, and turions.

Turions are densely packed tiny football-shaped clusters of modified leaves at the end of each plant. As the growing season ends and the waterwheel senesces, the turions remain. These will sink to the wetland bottom by late November and float back up to the pond surface by early April. Turions are also tolerant of desiccation. Waterwheel can be moved by from birds, beavers, and even boats, on which it has been documented as a hitchhiker.

So how did the waterwheel get here? It is a long and sordid story, involving the intentional planting of the species in the late 1990s at various locations in NJ and NY, by well-intentioned individuals who hoped to provide refugial patches for the species in North America in case it went extinct in its native range. For those interested, Lamont et al. (2013) do an excellent job of documenting the introductions in North America. Though well-intentioned, these deliberate introductions may come back to haunt us, as this species spreads across eastern North America predating on native fauna and impacting habitats in ways we've never before seen. No documentation is available on the species that waterwheel consumes in North American wetlands.
Controlling waterwheel is a serious task, though there is little data on the topic. No control efforts have yet been successful in Virginia, where the most control work has been done. In 2014, 36 pounds of turions were collected and removed from a pond at Fort A.P. Hill, VA with no apparent impact to the waterwheel population in the subsequent year.

More images

Photographs courtesy of Fort A.P. Hill, US ARMY 2015. Photos available electronically on request.

For more information about Invasive Species of Concern in Maryland, visit the Maryland Invasive Species Council.

Additional Resources

Virginia Flora: Aldrovanda vesiculosa L.

IUCN Red List, Aldrovanda vesiculosa – Endangered

Aldrovanda vesiculosa project

The post The Waterwheel… Turning Over North American Wetlands first appeared on Maryland Invasive Species Council.

ANNAPOLIS, MD (December 1, 2015) – Exotic species are in the news almost daily. They can be found in our parks and even in our own backyards. Sadly, many of them are so common, most people do not realize that they do not belong here. To be invasive, an organism must have evolved somewhere other than where it's found in Maryland, have a negative impact on the environment it moves into, and have been moved, deliberately or by accident, by people.

For example, when the brown marmorated stink bug silently slipped into the U.S., it was years before it was correctly identified as an exotic species. By that time it was already becoming a pest in orchards and vineyards.

One of the first questions about most invasive species is "How did it get here?" — quickly followed by "Could it have been prevented?" The majority of invasive plant seed, disease and insect pests are accidentally introduced. How, you might ask? While the list of pathways is surprisingly long, the most common avenues are the movement of goods produced in foreign countries, travelers returning home with souvenirs, and internet sales. The U.S. Department of Agriculture (USDA) and Customs and Border Protection (CBP) work to prevent the introduction of such pests. In this month of increased holiday travel by both people and packages, the Maryland Invasive Species Council has chosen this prevention work as the topic for the December's "Invader of the Month".

Cargo is moved in large containers with products shrink-wrapped on pallets, in boxes, or simply loaded in trucks. This results in many small hiding places that insects, seeds, and snails can use to move, unbeknownst to them, all over the world. To prevent this from happening, CBP, a branch of the Department of Homeland Security, routinely inspects cargo. The searches are extensive and include examining the exterior of shipping containers for hitchhikers adhering to the undercarriage and walls. Inside the container, pallets are checked to ensure that they have been properly treated to prevent the movement of bark beetles and woodborers. Inspectors then move to the product being shipped. Flashlights, forceps and box-cutters are routinely used to open, inspect, and manipulate the products to ensure they are pest free. The final stage of an inspection is to sweep out the empty cargo container and look for any seeds or insects that were hiding in the corners.

Most people love escaping on vacation, but if you have ever traveled internationally you might recall filling out a declaration form before leaving the faraway airport to return home. Preventing the movement of pests in baggage is challenging and relies on several factors, including the declaration form. The declaration is a reminder to all passengers entering the US that bringing in certain items is prohibited. The declaration is a federal form and false claims are subject to penalty. To reinforce the urgency and in an attempt to keep people honest, CPB randomly selects passengers for screening, checks passenger lists against a database of previous violators, and walks the baggage floor with highly trained K9 units.

The last pathway of pest introduction is internet sales. The internet has drastically increased the average person's ability to buy products, knowingly or not, from foreign countries. Foreign markets are trying to meet the high demand for heirlooms and specialty varieties and non-GMO seeds for home gardeners. Small packets of seeds are easily mailed and are found only by hard work and highly trained K9 Units. Unfortunately, a recent study reports that our current biosecurity practices are not effectively preventing the trade of plant material via internet sales (Humair et al. 2015).

You can contribute to the economic and ecological safety of the US and your own backyard by being a careful and conscientious traveler and internet purchaser. Know what you're importing, where it comes from, and make sure it's legal.Given the sheer volume of cargo, baggage and mail entering the US on a daily basis, it is unrealistic to believe that every pest will be found. Pests such as the tomato leaf miner (Tuta absoluta), wheat bug (Nysius huttoni), oak ambrosia beetle (Platypus quercivorus) and Asiatic brown rot (Monilia polystroma) are known threats. Unfortunately there are hundreds of species like them that not only threaten our neighborhoods but the entire U.S. economy. In response to this ongoing threat, the US Department of Agriculture (USDA) has established several programs to eradicate, or at least mediate the impacts of, new pests. Examples of this work include recalling products found to be infested or in violation of federal regulations, conducting surveys in and around the ports where cargo first enters the US and pests are most likely to establish, and providing funding to perform trapping across the country for high risk pests.

For more information about Invasive Species of Concern in Maryland, visit the Maryland Invasive Species Council.

photos available electronically on request.

References

Humair, Franziska, Luc Humair, Fabian Kuhn and Christoph Kueffer. 2015. E-commerce trade in invasive plants. Conserv. Bio. (in press)

US Department of Homeland Security, U.S. Customs and Border Protection. CBP Form 6059B (04/14)

Additional Resources

Animal and Plant Health Inspection Service

The post Preventing Invaders first appeared on Maryland Invasive Species Council.