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Hemlock woolly adelgid, a pest native to East Asia, threatens hemlock forests in the eastern US. You can help researchers better understand the activity of this pest and time management activities.

Image credit:
Connecticut Agricultural Experiment Station Archive,

Hemlock Woolly Adelgid Phenology Project

Project Background

New York State Hemlock Initiative logo

Hemlock Woolly Adelgid (Adelges tsugae) is an aphid-like invasive forest pest that lives, feeds, and reproduces exclusively on hemlock trees (genus Tsuga). Hemlock woolly adelgid (HWA) gets it name from the white, woolly mass that it grows from November-May. The insect’s presence kills buds on infested branches which prevents new twig and needle growth, eventually killing the tree in 4-20 years.

Currently, little is known about hemlock woolly adelgid (HWA) phenology across the landscape. A deeper understanding of the life cycle of HWA can tell managers where and when to release biocontrol insects, where to monitor for biocontrol establishment, and allow them to track HWA responses to different climate factors in the field. The New York State Hemlock Initiative seeks to engage citizen scientists in submitting observations on HWA to fill in the gaps in data. 

Join us!

Help scientists better understand when hemlock woolly adelgid insects are active and most susceptible to treatment by reporting when you see this pest in various life cycle stages. 

There are two main activity periods for HWA. In the winter and spring, observers look for egg laying. From the end of the summer until the end of the fall, observers look for the growth of HWA post-dormant nymphs (which look like black sesame seeds in a white halo under a hand lens) as they wake from their summer inactivity. 

How to Participate

1. Join Nature's Notebook. If you haven't already, create a Nature's Notebook account. See our specifics of observing if you need more details on getting started. You can set up a phenology monitoring site in your backyard or another location you frequent.

2. Take observations. For this effort, we are seeking observations on the following life cycle stages of hemlock woolly adelgid:

Phenophase Definition Photo (click to enlarge)
Active Adults One or more adults are seen moving about or at rest. For Adelges tsugae, the wingless, "wool"-covered, adult females are settled in one spot on a plant, usually at the base of a needle on the most recent twig growth, and do not move. Also include "wool"-covered instars as they are difficult to distinguish from adults. Active Adults Photo: Kate O'Conner NY State Hemlock InitiativeInfo
Eggs One or more eggs are seen. The small, brownish-orange eggs are present when the white, woolly sac around an adult female appears puffy, generally starting in the early spring, and can be seen by gently scraping the "wool" aside.  Hemlock woolly adelgid eggs, photo: Nick Dietschler
Active nymphs One or more nymphs are seen moving about or at rest. Nymphs ("crawlers") are reddish-brown in color and move around before settling in one spot on a plant. Hemlock woolly adelgid crawler Photo: Kelly Oten, North Carolina Forest Service, 
Inactive nymphs One or more nymphs are seen in a dormant state. Nymphs settle in one spot, usually at the base of a needle, turn black in color with a small halo of white "wool", and enter dormancy (aestivation) between midsummer and fall.  Hemlock woolly adelgid inactive nymphs, photo: Nick Dietschler
Post-dormant nymphs One or more nymphs have come out of their dormant state. The post-dormant nymphs are still settled in one spot but are increasing in size and wooliness, and changing color from black to grey. Do not include individuals that have molted and shed their exoskeleton, often appearing as if another adelgid is riding on top of them. These individuals are "wool"-covered instars that can be considered "Active adults."  Hemlock wooly adelgid post-dormant nymphs, photo: Nick Dietschler

Observation tip: Nymphs are tiny! See how they compare to the size of a penny here.

The USA-NPN makes available Pheno Forecast maps that indicate when you will be most likely to see hemlock woolly adelgid eggs and active nymphs in your area. 

See the HWA Forecast

3. Report your observations. As you collect data during the season, log into your Nature's Notebook account and enter the observation data you record. You can also use our smartphone apps to submit your observations.


Questions about this effort? Contact