Keeping the Legacy Alive

HWA Survey Methods

© Connecticut Agricultural Experiment Station Archive
Telltale Signs of HWA in Late Fall - Early Spring

HWA is easiest to identify by the presence of small woolly masses on the underside of Hemlock twigs, near the base of the needles which can be seen in late Fall,Winter, and early Spring. HWA goes through four development stages or “instars” as it secretes its “wool” then lays its eggs as an adult. During this time an infestation will be characterized by white, waxy masses that are secreted around the bodies of the insect, always clumped on twigs near the base of the hemlock needles. Tips: Sometimes the infestation is best seen while looking at the underside of a hemlock twig. In the case of a lighter infestation you may only see one or two woolly masses present. The photo to the left shows a heavy infestation.

© S. Hudson
Telltale signs of HWA in Late Spring - Early Fall

 In late Spring-Early Fall HWA is not growing, they are in a dormancy period known as aestivation. This time of year HWA appears as small, black nymphs, called sistens, at the base of hemlock needles on tree’s new growth. The sesame seed-shaped sistens will have a distinct white halo. Finding HWA at this time of year may require use of a magnifying glass or hand lens (7x or 10x magnification). Tips: It may help to look at underside of twigs for HWA; remnants of wool from previous season may also be present.

© C. Gray
Tree Damage

On trees, look for premature needle loss, dieback of twigs and branches and thinning crowns. Symptoms will progress to fading, thinning and dying limbs, with die off beginning at the base of the tree and moving upwards. 

© C. Gray
A Noticeable Gray Casting

From a distance, a noticeable grey casting can been seen in infected hemlock patches. An indication that Hemlock Woolly Adelgid has been present for some time. 

© C. Gray
Remnant Egg Sacs

Look for remnant egg sacs on the tree trunks, especially when wet. Hemlock Woolly Adelgid may not be detected if there are no reachable branches without the use of other detection tools, so checking tree trunks for remnant egg sacs may be one of the only ways to confirm the presence of HWA. 

© C. Gray
Young Hemlock Seedlings to Large Old-Growth

Check all sizes and ages of hemlock from the forest floor to high in the canopy. HWA has been found on young hemlock seedlings and on large old-growth hemlocks.

© C. Gray
Fallen Branches

Look for fallen branches from the trees canopy on the forest floor especially after a wind storm. HWA could go undetected in the lower branches but reveal HWA from above. In some older hemlock stands it is difficult to reach the upper branches so taking advantage of the windfalls.     

© D. Brown


HWA Imposters

Don't be fooled by these common imposters on hemlock, such as this spittle bug! Many things look like hemlock woolly adelgid at first glance. On closer inspection, they can be ruled out either because of their texture, their location or another characteristic. Remember, HWA will usually be found on the undersides of twigs at the bases of needles and is coated with a waxy material.



Spider egg sacs can be large to medium balls of webbing, often connecting multiple needles and twigs. At first glance they can also look somewhat like HWA and require a second closer look.(not harmful) 





The Oak skeletonizer spends the winter months in small, white cocoons resembling ribbed grains of rice. The cocoons may be attached to fallen leaves, branches and limbs.In the spring, tiny little moths emerge and lay eggs on leaves where the larvae feed until they move off the host to pupate and begin the cycle again. Oak skeletonizer is often found on hemlock needles.

© S. Limbu

© C. Gray
Detection Tools

Slingshot sampling with a velcro covered ball shot into the upper canopy of hemlock trees using the slingshot to sample for hemlock woolly adelgid.





Another detection tool is the pole pruners that can reach into the upper branches to detect a light infestation that could be missed otherwise.


HWA Biosecurity Checklist

It is important to keep in mind that there is always a possibility of spreading HWA to uneffected areas, therefore if you know that the area you have surveyed has HWA present or suspect that it may, please follow the checklist below to help prevent further spread!

  • Use a lint roller to remove potential crawlers from clothing once you have left the forest stand
  • Beat and/or lint roll hats and coats
  • Avoid placing gear on or near hemlock trees
  • If possible, avoid visiting hemlock stands in uninfested areas for several days
  • Do not collect branch samples or specimens, photograph instead
  • Do not bring your pet into infested stands
  • Wearing light coloured clothing could assist with detecting and removing crawlers
  • Do not park your vehicle near or under hemlock trees
  • Launder all clothing prior to re-entering the field
HOW TO: Sticky Trap Sampling for Hemlock Woolly Adelgid
HOW TO: Ball Sampling for Hemlock Woolly Adelgid