There are a few invasive animal species that threaten trees at West Rock, and one potential threat that has thankfully not arrived in the area. The existing threats are the non-native woolly adelgid, emerald ash borer and gypsy moths. The native eastern tent caterpillar is also a problem. Finally, the spotted lanternfly is a pest that is just beginning to arrive in Connecticut.
Animal Invasive: Woolly Adelgid
Perhaps the biggest devastation at West Rock has been caused by a tiny insect called the woolly adelgid. This tiny creature sucks sap from the needles of the Eastern Hemlock tree, gradually killing the tree over a period of about five years. Somewhere in this story there is a metaphor about the mighty being felled by the tiny, as the woolly adelgid is too small to be seen without magnification, and hemlock trees can grow to 150 feet tall and live for 400 or more years. The woolly adelgid is visible by the white egg sacs that give the insect its name. These egg sacs cling to the underside of the needles of infested trees.
The devastation at West Rock is most visible along the Regicides Trail where the trunks of felled hemlocks continue to lie alongside the trail. I can only imagine the shade they once provided along this ridgeline trail. A healthy hemlock is truly a magnificent tree with vibrant green needles that stretch from ground to crown. Unlike the white pine, hemlocks thrive in shade and keep all of their needles. White pines die in shaded areas and even in sunny areas, will gradually drop their needles on their lower branches as they are shaded by the upper branches.
An infected hemlock has a sickly greenish gray cast to its needles, no needles on the lower branches, and as the insect advances up the tree, fewer and fewer branches have needles. There are places in West Rock that still have isolated, healthy hemlocks.
The woolly adelgid has difficulty surviving in temperatures below -5 degrees Fahrenheit, which is positive news after the frigid temperatures in some recent winters with greater than 80 percent mortality in 2014, 2016 and 2018.
The adelgid has no predators in the United States, but does get eaten by a Japanese ladybug that the state has tested as a measure of biological control.
In a residential setting, the adelgid can be controlled by an oil or injection applied by a trained arborist. In the woods, there is no present and practical way of chemical control.
Links:
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| This tall hemlock tree leans across the Regicides Trail in Aug. 2017 after being killed by the woolly adelgid. The Regicides Trail used to be lined with hemlock trees that created cool shade along the top of the ridge, but they have been mostly killed off by the invasive insect. |
Animal Invasive: Emerald Ash Borer Invades West Rock
The emerald ash borer, an insect native to Asia, has killed the ash trees at West Rock Ridge State Park and there is no practical solution at the moment to save them in the forest. I have seen young ash trees growing, but how long they can avoid the borer remains to be seen.
Dead ash trees are widespread throughout Connecticut and locally can be seen across different parts of West Rock, along the Sanford Feeder, which is Regional Water Authority property, and on the Darling House property in Woodbridge.
The larvae kill the trees by eating phloem, cambium, and xylem inside the bark, which disrupts the flow of nutrients in the tree. A tree typically dies within two to three years of being infested. One concern is that the dead trees are prone to simply falling over, which presents a hazard to forest users. The other concern is the loss of an important forest tree.
Ash trees are estimated to comprise 5 percent of the trees in a forest. From my own informal observations, I see ash trees in scattered located at West Rock where oak, beech, birch, and maple trees are far more common. One positive sign in this infestation is that the borer feeds exclusively on ash trees, so other native trees will not be harmed.
The dead trees are mostly easily recognized by a phenomenon called “blonding” in which woodpeckers strip off the dark outer bark to reach the borer larvae, leaving the light-colored inner bark showing. Another telltale sign of borer damage is the D-shaped holes created by the adult insects where they tunnel out of the trees; the flat part of the D is on the top of the holes. If the bark is completely removed, the tunneling from the larvae is clearly visible.
The bright green colored adults are about a third to a half inch long. The adults resemble the native six-spotted tiger beetle. The state is investigating the use of a parasitic wasp from Asia to kill the eggs and larvae. For ash trees on cultivated properties, insecticides are a possibility to save trees that are not heavily infested.
The insect was first spotted in Michigan in 2002, and likely arrived on wood packaging materials from Asia. The borer has spread rapidly across the country, arriving in Prospect, Conn. in 2012. Sightings were confirmed in Hamden in 2014.
The most important advice people can follow is “don’t move firewood,” as moving infested ash trees is one reason why the borer spread so rapidly. The state had strict regulations regarding the movement of firewood, as a result of the borer infestation.
Some of the information from this article came from the following websites, which have more details than this quick article can provide:
Connecticut Agricultural Experiment Station: https://portal.ct.gov/CAES/Publications/Publications/Emerald-Ash-Borer-Agrilus-planipennis
Connecticut Department of Energy and Environmental Protection: https://portal.ct.gov/DEEP/Forestry/Forest-Protection/Emerald-Ash-Borer-EAB Midwest-based Emerald Ash Borer Information Network: http://www.emeraldashborer.info/
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| This ash tree along the Regicides Trail in January 2017 shows extensive "blonding" caused by woodpeckers stripping away the darker outer bark to get at the emerald ash borers that killed the tree. |
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| A closer look of the "blonding" caused by woodpeckers stripping away the darker outer bark of an ash tree. Small "D" holes are visible in the bark. |
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| An even closer look of the "blonding" caused by woodpeckers stripping away the darker outer bark of an ash tree. Small "D" holes are visible in the bark. The adult emerald ash borers create these holes when they tunnel out of the tree. |
Animal Invasive: Spongy Moth Caterpillars
The spongy moth caterpillar (previously called the gypsy moth caterpillar) is present at West Rock, but not in large numbers. West Rock was spared the destruction that central and eastern Connecticut endured in 2016 and 2017 when gypsy moth caterpillars denuded oak trees, their favorite food. They had a definite impact on the woods in adjacent Woodbridge, as seen in the photo below.
Their egg sacs are a tan oval about the size of a quarter that can be seen on trees. Experts say that simply scraping them off the tree is not enough; the eggs need to be soaked in oil, or covered in soapy water to kill them. The caterpillars are distinctive with their gray-black bodies with blue and red dots.
In 2015, I found many dead caterpillars along the Yellow Trail, apparently killed by the fungus that is fatal to them. In 2016, there was so little rain, the fungus was not activated. There was plenty of rain in Connecticut in 2017, but the caterpillars ate through many trees before it activated.
Information from the state of Connecticut on spongy moths: https://portal.ct.gov/deep/forestry/forest-protection/the-spongy-moth-in-connecticut-an-overview
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| The thin canopies of trees attacked by spongy moth caterpillars can be seen in Woodbridge in this view from the Regicides Trail, June 2017. |
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A spongy moth caterpillar crawls along a fern on the Darling House Trails in Woodbridge, June 2017. |
Undesirable Native Insect: Eastern Tent Caterpillar
The eastern tent caterpillar is sometimes mistaken for gypsy moths, but their tents, usually found in the forks of cherry trees are unmistakable. While native, they cause problems for cherry and other fruit trees by munching on their leaves. Breaking open the tents with a stick allows birds to eat them. Links:
https://portal.ct.gov/-/media/CAES/DOCUMENTS/Publications/Bulletins/B378pdf.pdf
Animal Invasive: Spotted Lanternfly
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The white protective tent created by eastern tent caterpillars is very visible along the Regicides Trail, May 2017. |
Animal Invasive: Spotted Lanternfly
The spotted lanternfly is a destructive insect from Asia that feeds on a variety of trees, particularly fruit bearing trees. I first spotted this invasive pest at West Rock in July 2024 along Mountain Road, and Aug. 2024 along Baldwin Drive.
The preferred host for this insect is the invasive tree of heaven, which is also native to Asia. The spotted lanternfly is another compelling reasons to cut down tree of heaven. I continue to cut down this tree when possible and girdle the bark to kill the larger ones.
People are encouraged to kill this pest in any form, and to scrape its egg masses off tree bark.
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A spotted lanternfly nymph crawls on a tree of heaven along Mountain Road in July 2024. |
Animal Invasive: Foliar Nematode
The foliar nematode is a microscopic roundworm that feeds on the leaves of beech trees, eventually killing the tree. This infection is called Beech Leaf Disease. The leaves of affected trees are crinkled and appear to be melted. Scientists from the Connecticut Agriculture Extension Station (CAES) are studying the nematode, which they determined has come from Japan. The nematode first appeared in southern Connecticut in 2020. The scientists are studying possible treatments for trees, but as of 2024, any treatments are not practical for woodland situations.
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A small beech tree along the Sanford Feeder Trail in May 2023 shows the beginning signs of Beech Leaf Disease with the characteristic wrinkling of leaves. |
Animal Invasive: Asian Longhorn Beetles (not yet in the area)
The Asian longhorn beetles is another worrisome insect from Asia that attacks trees. This one has not been seen in Connecticut, but remains a threat.
Animal Invasive: The Graffiti Artist and Litterbug
This is a two-legged invasive that somehow think is it okay to spray paint words and drawings on the park’s rock surfaces and the pavement at Baldwin Drive. I have yet to catch anyone and don’t know how to control them, but they certainly detract from the park’s beauty. Some will carve their initials into trees.
The litterbug variation leaves behind bottles, cans, cigarette wrappers and other trash. They somehow think that tossing the trash into the weeds, where it is harder to retrieve, is somehow better than just leaving it along the parking lot.
The litterbug variation leaves behind bottles, cans, cigarette wrappers and other trash. They somehow think that tossing the trash into the weeds, where it is harder to retrieve, is somehow better than just leaving it along the parking lot.
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| Painted-over graffiti on the pavilion at the South Overlook, as seen from the Regicides Trail. |
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