December 2019
Zebra Mussels Now in Lake Marble Falls, Worsen in Granger Lake

Lake Marble Falls, upstream of Austin on the Colorado River, on Thursday joined a growing list of Texas lakes infested with invasive zebra mussels (Dreissena polymorpha), according to the Texas Parks and Wildlife Department.

Lower Colorado River Authority biologists confirmed the presence of zebra mussels in Lake Marble Falls after finding mussels as well as larvae at multiple sites this fall, a statement from Texas Parks and Wildlife said. Biologists said they expected the zebra mussels to spread downstream to Lake Marble Falls because Lake LBJ had previously been found to be infested with the invasive mollusk.

Granger Lake in Williamson County was also upgraded from "positive" to "infested" Thursday after biologists repeatedly found zebra mussel and their larvae throughout the lake, the TWPD statement said.

The rapidly reproducing zebra mussels can have serious economic, recreational and environmental effects on Texas reservoirs and rivers, the statement said.

Zebra mussels are in 29 Texas lakes across five river basins as of November.

zebra mussels on rope
Credit: Hans Landel,, LBJWC

Researchers Studying Invasive Slugs in Texas for Harmful Nematodes

Several invasive slugs and one flatworm species present in Texas are becoming a human health concern, because they can transmit Angiostrongylus nematodes to mammals. Those slug species are the Black Velvet Leatherleaf slug (Belocaulus angustipes), Yellow Garden slug (Limax flavus), Giant Garden slug (Limax maximus) and Marsh slug (Deroceras laeve); and the flatworm is the New Guinea flatworm (Platydemus manokwari). The slugs are found throughout the state, and through citizen reporting and TISI expert collections, we have documented the New Guinea flatworm in Gulf Coastal and Central Texas.

Over the past three years, the Texas Invasive Species Institute (TISI) has been documenting the true distribution of these species, and in late 2018, they started testing these slugs and flatworm for Angiostrongylus nematodes. The Rat Lungworm (Angiostrongylus cantonensis) and Intestinal Angiostrongyliasis (Angiostrongylus costaricensis) are the two species of concern for TISI. The Rat Lungworm is native to southeastern Asia but is found in Alabama, California, Florida, Hawaii, Louisiana, Mississippi and Oklahoma, while Intestinal Angiostrongyliasis is native to Central America and was once documented in Texas in the 1970s. In order to complete their lifecycle, Angiostrongylus species requires one mollusk (snail/slug) host and one mammal host. The TISI is focused on testing slugs/flatworm because the nematodes reach their infective larval (L3) stage within them, and those L3 are excreted in their slime trails.

In their native lands, these nematodes are often transmitted to humans eating raw or undercooked slugs and snails; however, in the USA, we are subject to exposure through the handling of infected slugs and/or garden vegetables/fruits covered with contaminated slime trails. Prevention of these nematodes is very easy: just simply washing your hands, fruits or vegetables can significantly reduce any exposure to Angiostrongylus.

TISI is still actively accepting sighting information and slug specimens. If you think you have one of these species, please email a photo and your location to Ashley Morgan-Olvera at for confirmation.

Black velvet leatherleaf slug
Black velvet leatherleaf slug. Credit: Tim Searfoss, TISI Citizen Reporter

Giant garden slug
Giant golden slug. Credit: Jesse Berryhill, TISI Citizen Reporter

Marsh slug
Marsh slug. Credit: Dustin Pfannenstiel, TISI Citizen Reporter

Yellow garden slug
Yellow garden slug. Credit: Amanda Smith, TISI Citizen Reporter

New Bipartisan Legislation Introduced to Stop the Spread of Aquatic Invasive Species, Including in Texas

U.S. Senators Michael Bennet (D-Colo.), Steve Daines (R-Mont.), and Jon Tester (D-Mont.) introduced the Stop the Spread of Invasive Mussels Act of 2019, new legislation to slow the movement of aquatic invasive species, like zebra and quagga mussels (Dreissena polymorpha and D. bugensis), into Western States, including Texas. The bill authorizes the federal government to assist states in building and staffing new inspection stations. For more information, see this news release, this explanation of the bill, and the bill itself.

US Capitol

Measuring the Cost of an Invasive Tree Killer

For the first time, a study has attempted to assess the devastation caused by the emerald ash borer (Agrilus planipennis) in US forests that shape river systems. Researchers discovered a variety of ways that the ecologically vital habitat is being systematically changed at a landscape level as tens of millions of ash trees disappear.

The cost to the nation's economy has been estimated to exceed $10 billion. However, a team from Michigan State University saw that little attention had been paid to how the invasion was changing the face of riparian (water/river system) forests. Effects they found included whether dead ash trees remained standing or fell and began to decay, contributing to soil nutrients; logjams in streams; conversion from closed-canopy to open herbaceous ground cover, especially sedges; fewer invasive species infesting than expected; a large ash sapling cohort; and the loss of seeds from the now-gone adult trees, which not only lowers recruitment but also meant less food for the animals that rely on the seed.

emerald ash borer with wings spread
Credit: David Cappaert, Michigan State University

Crews to Begin Removing Invasive Species from Suter Wildlife Refuge

The Suter Wildlife Refuge in Corpus Christi is about to get a huge makeover that will take several years to complete. The 72-acre park is covered with grasses, shrubs, and trees that are not native to the area. With a $30,000 grant from Citgo, the City of Corpus Christi will be partnering with American Conservation Experience to remove the invasive plant species to allow for native plants to repopulate the area.

"We intend for this to be a multi-year partnership to begin removing the invasive species in the park," said Jermel Stevenson, Director of Parks and Recreation.

For more information, see this story at

Credit: MJ, TripAdvisor

US National Parks Face "Crisis" Over Invasive Animal Species

More than half of America's national parks are facing a "deep and immediate threat": the ongoing presence and spread of invasive animal species, such as rats, cats and feral hogs. The National Park Service (NPS) has taken the first step in combating this invasion by asking a group of experts to help chart a course that will ensure the survival of these national treasures. The new report notes that, "Of the 1,409 reported populations of invasive species in National Parks, only 11% are under control."

Among the efforts the report says the NPS should make is collaboration with the public and with neighboring agencies. David Hallac, superintendent of the National Parks of Eastern North Carolina and co-author of the report, said, "Without a question, the best possible way to manage invasive animals is to prevent them from invading an ecosystem in the first place. And that can rarely be done alone by an individual park. That's something in which park managers have to absolutely partner with and work collaboratively with communities and adjacent land managers." The NPS must also develop better coordination among the parks, capitalize on emerging technologies, and improve management and monitoring.

Learn more at,, and

The original article published in Biological Invasions can be found here.

NPS logo feral cat and feral hog
Credit: feral hog - TPWD; feral cat - C. Potter, Department of the Environment, Australia

Texas Gulf Region Cooperative Weed Management Area to Hold Meeting and Work Day the Week of Port Aransas Whooping Crane Festival

The Texas Gulf Region Cooperative Weed Management Area (TGR-CWMA) will be holding its semiannual events in association with the Port Aransas Whooping Crane Festival. Its public meeting will be held February 18, 2 pm, location TBD. Everyone is encouraged to attend. Come and meet us, and hear what the CWMA has accomplished and what we are planning.

The TGR-CWMA will also conduct a workday 8 – 11 am at the Birding Center, to remove Brazilian peppertrees (Schinus terebinthifolia). Please dress appropriately and bring water. Tools and gloves provided, but bring your own gloves if you have them.

During the Whooping Crane Festival, February 21-23, the TGR-CWMA will have representatives at Paradise Pond and at a table at the Community Center. Stop by to see us and get information!

Keep your eye on the next iWire for more details.


Invasive Spotlight:
Sirex Woodwasp
(Sirex noctilio)

The sirex woodwasp is a large insect that attacks pines. Females drill holes through the bark to lay their eggs in the wood. In the process, they also inject a toxic mucus and a symbiotic fungus (Amylostereum areolatum), which together kill the tree while creating an environment in which the larvae can thrive. It has the potential to cause extensive damage across North America.

The sirex wood wasp is a member of a group of wasps called horntails because adults have a spear-shaped plate (cornus) at the tail end. It is a large, robust insect, usually 1.0 to 1.5 inches long. In general, its body is a dark metallic blue or black, although in males the middle segments of the abdomen are orange. Its legs are reddish-yellow, its feet black; however, males have thickened, black hind legs. Its antennae are entirely black. Females have a long ovipositor under the cornus. There are many native woodwasps, so positive identification of S. noctilio needs to be confirmed by an insect taxonomist.

Larvae are creamy white, legless, and have a distinctive dark spine at the rear of the abdomen. They create tunnels, or galleries, in the wood under the bark. When adults emerge after pupating in the wood, they chew round exit holes that are from 3 to 8 mm (1/8 to 3/8 in) wide.

The sirex woodwasp can attack live trees, unlike native woodwasps that only attack stressed, dying and dead trees. Foliage of infested trees initially wilts, and then changes color from dark green to yellow, and finally to red during the 3-6 months following attack. Infested trees may have resin beads or seeps at the egg laying sites.

This insect is originally from Europe, Asia and northern Africa. It was introduced inadvertently into New Zealand, Australia, Uruguay, Argentina, Brazil, Chile, and South Africa. The wasp was discovered in New York in 2004. It most likely hitchhiked in imported wood products. It is now found in Connecticut, Michigan, New York, Ohio, Pennsylvania, and Vermont. It is not yet found in Texas, and let’s keep it that way!

Because of its potential negative impacts in Texas, the sirex woodwasp is a Report It! species as part of the Sentinel Pest Network, a component of If you believe you have found a sirex woodwasp, please report this species. Because there are many native horntail wasps that might be confused with the sirex woodwasp, we ask that you collect a specimen to aid in identification. Don't worry, they don't sting.

Follow this link for more information on the sirex woodwasp.

 sirex woodwasps
Sirex wood wasp female (left) and male (right).
Credit: Vicky Klasmer, Instituto Nacional de Tecnologia Agropecuaria

sirex woodwasp larva

Sirex woodwasp larva.  Note dark spine at end of body.
Credit: Bernard Slippers (FABI, University of Pretoria)
sirex woodwasp damage: wilt
Left: Pine needles hanging down (wilted) and turning color.
Right: Red needles.
Credit: Dennis A. Haugen and Kent Loeffler (Dept. of Plant Pathology, Cornell University)
sirex woodwasp damage: sap weeping from wounds
Left: Sap weeping from egg laying sites.
Right: Larval galleries under the bark.
Credit: Dennis A. Haugen and Kent Loeffler (Dept. of Plant Pathology, Cornell University)

sirex woodwasp alert

More News

Integrated Approach for Managing Aquatic Invasive Species in California
Though small and somewhat nondescript, quagga and zebra mussels (Dreissena bugensis and D. polymorpha) pose a huge threat to local rivers, lakes and estuaries. Thanks to aggressive measures to prevent contamination, Santa Barbara County's waters have so far been clear of the invasive mollusks, but stewards of local waterways, reservoirs and water recreation areas remain vigilant to the possibility of infestation by these and other non-native organisms. Learn more at

Scientists Uncover Patterns That Predict Which Insects Will Harm North America’s Conifers.
Researchers have developed a set of models that were able to successfully identify which insects became pests on conifers in North America in the past. The models therefore may be able to predict which specialist insects might be deadly if they arrive in North America and which tree species are likely to be vulnerable. Interestingly, life history traits of the insects such as number of offspring produced or dispersal ability were not important. Learn more at

After Committing in April, Illinois Governor Holds Up Planning on Project to Stop Asian Carp
Outdoor sports advocates and environmentalists said Gov. J.B. Pritzker has been dragging his feet on allowing the U.S. Army Corps of Engineers to get started on a plan to keep Asian carp (Hypophthalmichthys spp., among others) out of Lake Michigan despite committing to the study in April. Learn more at

American Slipper Limpet Is Innocent in European Oyster Decline
Researchers have managed to shine some light on the population decline of the European oyster. Utilizing museum specimens collected over 200 years, they have concluded that the occurrence of the invasive American slipper limpet (Crepidula fornicate) is not one of the main causes for the oyster dying out -- unlike previously assumed. Learn more at

UK Study Investigates Diversity of Insects on Native and Non-native Garden Plants
Research finds that while native plants host the highest diversity of insects, non-native plants are also heavily used by insects, including some that are rare on native plants. Learn more at

Invasive Species Set to Exploit Climate Change in Antarctica
Scientists argue that the warming occurring in Antarctica will make it easier for non-native species
both to get a toe-hold there and to spread once there. And a big reason non-native species arrive on the continent is the tourists that come visit. Learn 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 Workshops

Invaders of Texas workshops train volunteers to detect and report invasive species as citizen scientists. Workshops, which are free, are designed to introduce participants to invasive species and the problems they cause, cover aspects of invasive species management, and teach identification of local invasive plants, and to train participants to report invasive plants using the TX Invaders mobile application. The workshop is 7 hours long (usually on a Saturday, but scheduling is arranged with each individual host group). The workshop satisfies Master Naturalist training requirements.

Sentinel Pest Network workshops serve to increase the awareness and early detection of a set of particularly important invasive species, to help prevent their spread into Texas or their further spread within Texas. Participants learn to identify species such as the Emerald Ash Borer, Cactus Moth, Asian Longhorned Beetle, and other pests of regulatory significance, and to report them. The workshop is 3.5 hours long. The workshop satisfies Master Naturalist training requirements.

Upcoming Workshops:

Saturday, February 15, 2020
Invaders of Texas Workshop
Location: Houston Advanced Research Center (The Woodlands, TX)
Contact: Teri MacArthur
(registration open soon)


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