August 2019
Invasive Zebra Mussels Found in More Central Texas Lakes

Texas Parks and Wildlife Department (TPWD) reports that established, reproducing populations of invasive zebra mussels have been discovered at two new lakes in Central Texas, Lake Lyndon B. Johnson (LBJ) in the Colorado River basin northwest of Austin and Lake Pflugerville northeast of Austin.

TPWD and Lower Colorado River Authority (LCRA) biologists confirmed the presence of zebra mussels in Lake LBJ at several locations. Zebra mussel larvae were also found in plankton samples. Zebra mussels are expected to spread downstream from Lake LBJ into Lake Marble Falls where they haven’t been found to date.

"It is disheartening to see zebra mussels spreading higher up the chain of the Highland Lakes in the Colorado River basin, as only boats can move this invasive species upstream to uninvaded reservoirs and downstream dispersal is inevitable," said Monica McGarrity, TPWD Senior Scientist for Aquatic Invasive Species Management [emphasis added]. Their introduction into these lakes "reinforces how critical it is for boaters to take steps to prevent their spread."

TPWD also confirmed the presence of zebra mussels at Lake Pflugerville after Inland Fisheries staff found adult zebra mussels attached to aquatic vegetation during a routine survey.

Meanwhile, Lakes Placid and McQueeney in the Guadalupe River basin, downstream of infested Canyon Lake, have been added to the list of 11 "positive" lakes where zebra mussels have been detected on more than one occasion.

“If you are going to be recreating on these and other lakes in Texas, it is essential to make the effort to prevent zebra mussels from spreading further," McGarrity said. “If you are on the lake for the day, take the time to properly clean, drain and dry your boat and gear before traveling to another lake. If you store a boat in the water on a lake with zebra mussels or work at a marina where boats are stored, please reach out to us directly to make sure proper decontamination procedures are being followed before any vessel is moved. A single mussel-fouled boat or barge can carry thousands of zebra mussels and cause a new lake to become infested."

In Texas, it is unlawful to possess or transport zebra mussels, dead or alive. Boaters are required to drain all water from all types and sizes of boats, whether powered or not, used on public waters before leaving or approaching a body of fresh water to prevent the transfer of zebra mussels and other invasive species.

Anyone who finds zebra mussels in lakes where they haven’t been found before or who spots them on boats, trailers or equipment that is being moved is encouraged to help prevent new introductions by immediately reporting the sighting to TPWD at (512) 389-4848, by emailing photos and location information to, or by using the Report It function of the website or mobile app.

More information about zebra mussels can be found online. A short instructional video on how to properly clean, drain and dry boats and equipment can be found on the TPWD YouTube channel. A status map and full list of these lakes can be found on the TPWD website.

zebra mussels on rope
(This is not from a Central Texas lake.) Credit: Hans Landel,

Lake LBJ
Credit: Lake LBJ Real Estate, Facebook

Clean, Drain, Dry poster

North American Invasive Species Forum

The North American Invasive Species Forum will be held September 30 – October 3, 2019 in Saratoga Springs, New York. The North American Invasive Species Forum is a biennial conference encompassing the interests of professionals and organizations involved in invasive species management, research, and regulation in North America. The 2019 Meeting will be a joint conference with the New York Invasive Species Research Institute out of Cornell University, an internationally renowned center of academic research and outreach.

The conference program will seek to bridge the geographic divide between West to East and North to South, connecting terrestrial and aquatic invasive species management, research, policy, and outreach initiatives and opportunities across North America. Presentations, workshops, tours, and special symposia will highlight successful initiatives that bridge the gap between geographic, political, and public-private boundaries.
Click here for more information.


Mussel Detection Dogs Returning to Lake Meredith

Over the Labor Day weekend, specially trained dogs will be at Lake Meredith, north of Amarillo, helping to inspect watercraft as well as the lake's shoreline itself for zebra mussels. These dogs are amazingly adept at sniffing out the invasive mollusk, and can inspect a boat much faster and more thoroughly than a person can, one to two minutes compared to 10 to 20 minutes. Any boat found with mussels will not be allowed to launch until it's been decontaminated. The dogs will be wearing booties as they inspect watercraft to eliminate any damage they might cause as they rove about the craft.

“The inspections are more about educating the public,” said Eric Smith, Superintendent at Lake Meredith National Recreation Area. “We want to ensure their bilges drain and that their ballast tanks drain, their live wells drain and it's to ensure that they're not moving water from one body of water to another."

Lake Meredith is free of zebra mussels, so please help to keep it that way.

For more information, see this article and accompanying video from KTX News.

zebra mussel dog

zebra mussel dog sniffing for mussels

Taxoplasm Parasite from House Cats Killing Sea Otters

As we know, cats can wreak havoc on their environment in many ways (see this previous article in the iWire). A recent study has demonstrated a further avenue of harm.

As a federally threatened species, sea otters (Enhydra lutris) face many threats. In California, one of these is the parasite, Toxoplasma gondii. The parasite enters the otter orally and makes its way to the brain, causing many problems and even death. If the parasite doesn’t kill the otter directly, it can render it more likely to be hit by a boat or eaten by a shark. Among sea otter carcasses examined over 4 years, T. gondii was determined to be the primary cause of death for 17% of otters, and contributed to mortality for an additional 12% (C. Kreuder et al. 2003: J. Wildl. Dis. 39, 495-509. [doi:10.7589/0090-3558-39.3.495]). New genetic research has now determined the source of the parasite: cats.

Several animal species can serve as hosts in the lifecycle of Toxoplasma, but only wild and domestic felids serve as "definitive hosts" - the hosts in which a parasite completes sexual reproduction. Because T. gondii reproduce in the gut, hundreds of millions of environmentally resistant oocysts are shed in the feces. Intermediate hosts, such as sea otters, can become infected by ingesting oocysts in contaminated food or water, or by consuming tissue cysts in infected prey. Sea otters do not typically prey on warm-blooded intermediate hosts of T. gondii (e.g., mammals and birds) and are likely infected via ingestion of oocysts that accumulate in coastal habitats receiving contaminated freshwater run-off. Several studies have demonstrated that oocysts are likely to accumulate in habitats where sea otters live, followed by acquisition of T. gondii by marine snails, an important sea otter prey item.

Using genetic analyses, researchers have shown that the same strains of Toxoplasma found in feral cats and a bobcat from local watersheds were found in the carcasses of sea otters, some of whom died primarily as a result of being infected. This is the first time a connection has been demonstrated between animals in terrestrial watersheds and those in marine shoreline waters. In this case, felids are apparently the source of T. gondii that infect some sea otters.

For more details, read this article in The New York Times.

Sea Otter
Credit: Marshal Hedin/Wikimedia Commons/CC-BY-SA-3.0/GFDL

Credit: Contra Costa Animal Services

toxoplasm lifecycle
Credit: E. Keats Shwab et al., PNAS July 17, 2018 115 (29) E6956-E6963;

What Happens When an Invasive Species Is Otherwise Endangered?

That's precisely the question facing some resource managers along the eastern United States coast. As an article in The New York Times reports, "Around the world, [a plant species] is going extinct. But from summer through late fall, the carnivorous, rootless, wetland-loving plant is plentiful in [a] swampy body of water near the Catskill Mountains." That plant is the waterwheel, Aldrovanda vesiculosa.

Closely related to the venus flytrap (Dionaea muscipula), these relatively small plants float just beneath the surface and, just like their relative, capture prey with leaves that snap shut instantly. They feed on any little animal that finds its way into a leaf, but seem to be especially adept at catching mosquito larva. Unfortunately, the waterwheel, which is native to Europe, Africa, Asia, and Australia, is highly endangered. A combination of over-collection and habitat loss and degradation have driven the species to the brink of extinction – at least in its native homelands. In an intriguing and, some would say, troubling twist, waterwheel has been introduced to water bodies in Virginia, New Jersey, and New York. And there, it is classified as either "invasive" or is on a state watch list. Like the Burmese python, which is threatened in its native range but highly invasive in the Florida Everglades, and a species of bumble bee that is disappearing in Britain but seems to be outcompeting native pollinators in Argentina, the waterwheel is presenting the dilemma of how to deal with an otherwise endangered or threatened species that is invasive, or potentially invasive, in its introduced range.

To help to save the waterwheel, conservationists in Europe have successfully reintroduced it, but they have also transplanted it to places its never been. Should the populations in the United States be allowed to flourish? Or should they be eradicated, to prevent their becoming another hydrilla, an outcome that is not certain? The answer seems to be both. For now.

Credit: Barry Rice,

fish caught by waterwheel
Credit: Alex Kawazaki

Invasive Spotlight:
Chinaberry Tree
(Melia azedarach)

Chinaberry is a tree that outcompetes native vegetation due to its high relative resistance to insects and pathogens and its quick growth. Its leaf litter raises soil pH, thus altering soil conditions for native plants and seed germination.

It is a deciduous tree that grows to 50 feet (15 m) in height and 2 feet (60 cm) in diameter. Its dark-green, deciduous leaves are distinctively multiply pinnately compound, giving them a lacy look, and have a musky odor. It produces clusters of lavender flowers in spring that yield poisonous yellow berries that persist through the winter.

In winter it may be confused with western soapberry (Sapindus saponaria) because the fruit are similar. However, Chinaberry fruit remain opaque during the winter, while soapberry fruit are translucent. They can't be confused when in leaf, as their leaves are completely different.

Chinaberry reproduces on-site primarily from root sprouts, and over longer distances via birds that feed on the abundant fruit and thus disperse the seeds.

It was introduced in the mid-1800s from Asia and is widely planted as an ornamental. It is now common on roadsides, at forest margins, and along riparian corridors. It cannot be killed by cutting, as it will simply resprout. If an individual is too large to be pulled, typically a method using herbicide will be necessary.

In Texas, Chinaberry is regulated by the Texas Department of Agriculture. It cannot be sold, distributed, or imported.

Follow this link to learn more about the Chinaberry tree.

Chinaberry Tree Leaves

Note the multiply-compound leaf in the foreground. Credit: John Huecksteadt, Invaders of Texas

Chinaberry Tree Berries

Credit: Invaders of Texas

soapberry berries

Soapberry berries for comparison. Credit: Norman G. Flaigg, NPONA, Lady Bird Johnson Wildflower Center

More News

Disease-Carrying Non-native Mosquitoes Push Northern Limits with Special Eggs
Invasive Asian tiger mosquitoes (Aedes albopictus) at the northern limit of their current range in North America are producing more of what are called diapause eggs than those from southern areas of their range, and those eggs survive better in winter. These special eggs have a very slow metabolism that allow them to survive winter or drying ponds. This new evidence of rapid local adaptation could have implications for efforts to control the spread of this invasive species. Read more at

Monster Tumbleweed: Invasive New Species Is Here to Stay
A new species of gigantic tumbleweed (Salsola ryanii) once predicted to go extinct is not only here to stay -- it's likely to expand its territory in North America. A new study supports the hypothesis that the new tumbleweed grows more vigorously than its progenitors because it is a hybrid with doubled pairs of its parents' chromosomes. Read more at

Global 88 Percent Decline of Big Freshwater Animals
Scientists have now quantified the global decline of big freshwater animals: From 1970 to 2012, global populations of freshwater megafauna declined by 88 percent - twice the loss of vertebrate populations on land or in the ocean. Large fish species are particularly affected. Read more at

Invasive Plants Negatively Impact Native but Not Exotic Animals
Biologists have completed a comprehensive meta-analytic review examining the ecological impacts of invasive plants by exploring how animals -- indigenous and exotic -- respond to these nonnative plants. Read more at

Asian Longhorned Beetle Larvae Eat Plant Tissues That Their Parents Cannot
The larval offspring of the wood-borer Asian longhorned beetle (Anoplophora glabripennis), native to China, can feed and thrive on tree species whose tissues would sicken their parents, perhaps explaining how the beetle expands its range, even when its preferred host trees are not nearby. Read more at

Non-Native Invasive Insects, Diseases Decreasing Carbon Stored in US Forests
Scientists have found that non-native invasive insects and diseases are reducing the amount of carbon stored in trees across the United States. Read more at

Python Wars: The Snake Epidemic Eating Away at Florida
Non-native parrots can cause substantial agricultural damage and threaten native biodiversity. A pan-European team of researchers, conservationists, wildlife managers and policy-makers worked together to conclude that measures to prevent parrots from invading new areas are paramount for limiting future harm. Read more at

How Red-Eared Invaders Are Hurting California's Native Turtles
Western pond turtles (Actinemys marmorata) got fatter and healthier after scientists removed nearly 200 invasive red-eared slider turtles (Trachemys scripta elegans) from the UC Davis Arboretum, reports a new study. The study is the first to quantify competition between these two species in the wild. Read more at


If you would like to highlight a successful invasive species project or nominate a special person to be highlighted in an upcoming iWire, please send the details to

Sentinel Pest Network and Invaders of Texas Species Workshops

Invaders of Texas workshops train volunteers to become citizen scientists to detect and report invasive species. Workshops, which are free, include information on the Sentinel Pest Network, which serves to increase the awareness and early detection of the Emerald Ash Borer, Cactus Moth, Asian Longhorned Beetle, and other pests of regulatory significance.

Workshops are tailored to meet the interests of your volunteer group, and supplementary session examples include an introduction to the TX Invaders mobile application and the Eradicator Calculator, a feature on designed to help organize and track volunteer-based eradication efforts.

Upcoming Workshops:

Tuesday, October 8, 2019 (6 pm)
Sentinel Pest Network Workshop

Location: Martin Dies, Jr. State Park, 634 Park Road 48 S (Jasper, TX)
Contact: Lori Horne
(Registration opening soon.)

For more information or to register to attend a free workshop, please visit the Workshop Page.