Invasive insect found in two new counties in 2023
An invasive insect is continuing to spread in Michigan. The hemlock woolly adelgid — also called the HWA — was found this year in two new counties: Benzie and Washtenaw. That brings the total number of counties where HWA has been found to seven: Allegan, Mason, Muskegon, Oceana, Ottawa, and now Benzie and Washtenaw. HWA is native to East Asia.
The insect feeds on hemlock trees by sucking out the tree's sap, which contains nutrients vital to the tree. It is a threat to ornamental hemlock trees and hemlock forests statewide.
Drew Rayner is the West Michigan HWA coordinator with the state Department of Natural Resources (DNR). He said Michigan's 170 million eastern hemlock trees are vital to their ecosystems.
"They're a really important tree here in Michigan. If we lose this tree, it could have impacts to wildlife, to birds, to overwintering habitat for animals like deer," Rayner explained. He added that hemlock forests shade streams and rivers, making certain cold-water fisheries possible.
Rayner said that fall and winter are good times to look for signs of infestation — white, cottony masses on the underside of hemlock needles — because, unlike many other insects, HWA begins to feed as temperatures cool.
The DNR is encouraging people who have hemlocks on their property to check them over. Hemlocks are cone- or egg-shaped conifers that have drooping, feathery branches. The needles are dark green on top, soft and flat with two parallel white stripes on the underside. The undersides of twigs and needles are where the HWA deposits its white ovisacs.
Rayner said state officials are well aware of the threat that HWA poses to Michigan's hemlocks.
"The state has been really proactive in addressing HWA. To date we've treated a little over 220,000 trees. We have a lot of people out there doing surveys and treatments...on that leading front of HWA, trying to slow the spread to uninfected parts of the state."