Last Updated 03 Jan 2023

Research Related to Hemlock Woolly Adelgids: An Extremely Invasive Species

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The hemlock woolly adelgid that attacks North American hemlocks. WA has spread along the East Coast from Georgia to Maine and now occupies nearly half the eastern range of native hemlocks. Since the findings in 1985, HWA has now spread through the Catskill Mountains and the Finger Lakes Region, into western NY. Once HWA hatch, they begin to suck out trees stored starches and as a result, do not allow trees to maintain themselves. In effect, many trees die just 4-10 years after they have been infested. As well, HWA does not follow a specific mating season, thus during the winter months, they are still reproducing at their average scale. In effect, the hemlock trees are unable correctly store glucose and necessary nutrients, for the HWA, are constantly utilizing the tree for its own benefit, therefore, the population of the trees begins to decrease exponentially.

Hemlocks are ecologically important, as they create unique environments because of their large, dense canopies. Because of this, they are extremely important to a variety of species, for they depend on them for food, protection, and ideal growing conditions. Furthermore, Hemlocks are essential for the stabilization of shallow soils, as they provide erosion control. Moreover, Hemlock trees are found on steep slopes, or low wetland, most often near streams of local water sources. As such, their placement around water allows both flora and fauna to utilize the tree, whether it be for shelter, nutrient-rich soil, or nutrients. The removal and decay of the hemlock trees can dramatically change an ecosystems process and may even result in the loss of unique plants and wildlife.

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In order to better understand the effects of the HWA, my investigation will evaluate the severity of the invasive species on hemlock trees. Cochecton New York holds a vast amount of flora and fauna in upstate New York, and as such, the hemlock trees are an essential aspect to the ecosystems present.


If there were to be a large presence of HWA in Cochecton, it would be plausible to conclude that not only are the Hemlock trees losing in population size, but also the biodiversity of other tree species in the area.


In order to analyze the tree diversity in Cochecton NY, I utilized a part of the forest in which my house is on and the Simpsons index. As such, I randomized the area, with the control being the measurements I used, 3x4m. In order to measure the area, I used a measuring tape and a stick to mark the area. Furthermore, in order to avoid the risks of disrupting local ecosystems, I made sure that I was extra careful while handling the land around me. Furthermore, to attempt to find any HWA, I used a small, handheld magnifying glass. Each hemlock I approached, I observed the tree, taking note of the color of its branches and the leaves, checking as much of the tree as I could, in order to find HWA’s.

Experimental Variables:

Named Variables

Equipment or procedure for measurement or control



Tree species

Tree identifier book

In order to ensure that each tree species I observed was correct.


The amount of HWA

The number of the types of tree species.

Magnifying glass.

To ensure that I wasn’t missing any minute or specific detail I could’ve missed with my bare eyes.


The measurements of the quadrants- 3x4m

The area in which I collected data: Cochecton, NY.

Map of property

Measuring tape.

To ensure that my measurements were as exact as possible and to make sure I knew where exactly to put down my quadrants.

Risk Factors:

There are many small ecosystems I could disrupt in the deciduous forest I was studying, therefore, I wanted to ensure that I was not disrupting them when walking around. In order to do so, I attempted to always stay on the designated path that runs through my property, and if I did have to step off the path, I was aware of any small patches or holes that could be home to warrens, skulks, or any other group of small animals that commonly burrow. As well, when I was collecting data, it was hunting season, and as such, was unable to go far into the forest as it posed a risk to my life.


Raw data: Sample 1 Sample 2 Sample 3 Sample 4 Sample 5

Woolly Adelgid

Hemlocks 1 2 2

White Pine 3 2 1 4

White Ash 1

Total 5 2 3 6

Total N= 16


n(n-1) 1 3 6 1 2 2 2 2 1 2 2 4 12 24

Total n= 16 Total n(n-1)= 24

D= 0.1 = Very low diversity.


With the results of the data, it is evident that there is little to no diversity in the area that I studied. The diversity of each tree I found and/or cataloged was relatively the same in each area, being that hemlock trees were increasingly dominant in some areas and not in others. As well, the hemlock trees were most often found by steep slopes and the stream that runs through my property, and as such, the diversity of tree species in those areas is not diverse, for there aren’t as many trees that gather near/on very steep slopes, most especially during the colder seasons. This is because the soil in that area is most affected by soil erosion during winter and fall, thus most tree species do not have direct access to nutrient soils. However, whenever I found a few hemlock trees, I noticed, and the data suggests, that there is more tree diversity surrounding them. For example, in sample one, I found 1 hemlock, 3 pines, and 1 white ash in the area in which the randomly chosen quadrant was. From the results of this data, it can be hypothesized that where there are more hemlock trees, there are most often higher percentages of diversity in terms of flora, as well as probably fauna.

Although my data suggests that there was very low diversity of tree species in Cochecton, New York, it is plausible that it is not as a result of Hemlock Woolly Adelgids. When looking for HWA in each quadrant, I found none. When doing further research into the specific regions which the HWA are most often found, I noticed that they gather near the lower half of New York state, including Cochecton, NY.

= Cochecton area

When doing further research into the specific regions which the HWA are most often found, I noticed that they gather near the lower half of New York state, including Cochecton, NY. However, my data and diversity index suggested that there were no woolly adelgids. Despite the absence of woolly adelgids on my property, there was still very low tree diversity. This is most likely because areas near streams or bodies of water in deciduous forests naturally have very low tree diversity, for the steep slopes and wetland makes it increasingly difficult for a multitude of tree species to thrive on.

= Significant natural


= Rare plants or animals

= Location

As well, according to this environmental resource mapper, created by NY’s department of environmental conservation, the area in which I was collecting my data, there are no essential ecosystems or rare species found. As such, my data suggests that because there were no significant natural communities, the HWA would most likely not gather in my area, but rather the areas in which obtain essential ecosystem, in order to find better quantities of resources.


Although I was unable to find any HWA during my data collection, I was able to identify and observe how hemlock trees affect the ecosystems in a deciduous forest.

The deciduous forest I researched had large quantities of dry deposition, such as snow, and it was unusually cold for that time, being somewhere between 10 to -10 degrees Celsius throughout the day. As such, the biodiversity of the area is extremely low, as the flora had fully decomposed. However, despite the low biodiversity in the area during winters, especially, HWA most often don’t need high amounts of diversity, as they use Hemlock tree’s through the winter to sustain themselves. Most HWA actually thrives during the winter, as they have limited predatory competitors, therefore allowing the reproduce at a rapid rate. What I found surprising is that because of this, I expected to see HWA in the area, as they are very common in upstate New York, however, there were none. In effect, I came to the conclusion that either the HWA were not present in the area as a result of plainly not populating that area, or that because of the unusually low biodiversity and lack of hemlocks as a result, the HWA’s had died during the beginning of winter.


After looking over and analyzing my data, I noticed that the number of tree types I utilized in my data was quite small, being just 3 different species of trees. As such, I was unable to take note of other tree types, and in effect, making my conclusion less accountable, than if I were to observe more tree species. Furthermore, I only took 5 samples, with a small amount of space within each quadrat. As such, I could’ve missed an abundance of trees, specifically hemlock trees, which had HWA. The biggest limitation I faced was my sampling strategy and planning. Since I used a randomized quadrant strategy, I faced some bais, in which I chose tree’s that did not look well, or we pratically dead. As such, I was faced with more biased and condensed data, limiting my ability to fully analyze flora and fauna. Moreover, when I collected my data, it was winter and hunting season, therefore I wasn’t able to go further into my property, limiting my perception and collection of proper data.

If I were to redo this experiment, I would still use the Simpsons index, but instead of utilizing a randomized approach, in terms of choosing the area in which to collect data, I would decide beforehand and use a transect with systematic quadrants along it, or a linear approach, in which each quadrant is 1 meter away from one another. In effect, my variable would be even more controlled and I would be able to find more samples, as the area in which I collect my data would be systemized, thus allowing for larger and more controlled data collection, rather than randomized points of data. As well, I would try to collect more samples, by creating more quadrants, and as such, my data might be more accurate.


Hemlock Woolly Adelgids is an extremely invasive species and can be difficult to prevent and get rid of. Hemlock Woolly Adelgids don’t have a specific mating season, thus allowing them to survive through harsh winters, using hemlock trees in order to survive. In recent years, states have recommended the use of Soil injections or a long term biologic control with the use of rearing predator beetles, called Galerucella beetles. The beetles have yet to be used, but scientists do expect that they will be effective, as they are a long term solution and will effectively kill HWA’s without causing any serious harm to Hemlock trees and other flora in the area. Soil injections, however, have been used throughout New York, as the technique entails injecting a “concentrated insecticide suspension at 2 to 5 depth around the base of the tree using a low volume soil injector.” The process of soil injections can be immensely effective, as it is long lasting and kills the HWA attached to a specific Hemlock tree, rather than spreading throughout other trees, thus causing more damage than good. Moreover, the direct injection of insecticide into the tree can be used in environmentally-sensitive areas, as there is little non-target organism exposure. As such, the soil injection can also be used on sites where soil drenching might not be practical: excessively wet, sandy, or compacted environments.

Though there are multiple benefits of soil injection, there are also limits and weaknesses. Soil injections can be very costly, thus limiting the demographic that have access to the equipment. As well, injections are labor intensive and do not allow people who might be weaker than others to use. The injections can cause wounding and injury to the roots and trunk of the tree, therefore posing a risk to the tree itself. Moreover, pesticides contain harmful chemicals to other flora and fauna, and by utilizing a soil injection method, poses a risk to the food chain. For example, if flora utilizes the soil near a recently injected hemlock tree, they are also absorbing the harsh chemicals, however, it is important to note that most hardwood trees will eventually heal, while palms will not. 

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