TRAVERSE CITY — Audrey Menninga and Andy Harmon plodded into the woods on snowshoes, on a mission to help halt the spread of yet another problematic invasive species.

Local environmental officials are busy tracking the progress of a new invasive pest insect making its way north along the Lake Michigan shoreline: the hemlock woolly adelgid. Menninga and Harmon are survey technicians for the Northwest Michigan Invasive Species Network who are spending this winter trekking through local woods in search of signs of the invasive pest.

The bug, often called by acronym HWA, is native to East Asia and feeds by sucking nutrients from hemlock trees. Individual insects are nearly microscopic, Harmon said, so the best time to spot the creatures is during winter months when their ova sacs can be seen with the naked eye as "white, cottony, little balls" clinging the the bottom of hemlock needles.

"You'll never see the crawler, but you will see the ova sac," Menninga said.

This week, the survey technician duo inspected hemlocks at Timbers Recreation Area in Long Lake Township, a property protected by the Grand Traverse Regional Land Conservancy. It makes the 34th site they surveyed already this winter.

The technicians check at least four branches on each hemlock they come across. Some sites take more time than others to cover, depending on the forest type.

For example, it took upwards of five days to survey Arcadia Dunes preserve, Menninga said, and she suspects it may take an entire season to cover Sleeping Bear Dunes National Lakeshore once it's targeted for survey work.

Experts suspect HWA have spread north along the Lake Michigan shoreline as hitchhikers on humans.

"A lot of it is probably hiking trails," Menninga said, adding campgrounds and parks to the list.

Damage caused by HWA insects ultimately may kill hemlock trees.

Harmon said the bugs consume nutrients from the tree at the base of the evergreen needles. The tree recognizes the threat and cuts off energy to the needles, which will die and drop to the forest floor. That means the tree can't photosynthesize, so it must live on its energy reserves until it either heals or dies, he said.

Hemlocks are shade-tolerant, long-living trees which provide critical food, habitat, shelter and ideal winter cover for both birds and mammals. The loss of hemlock forests in the northeastern part of the country led to increased erosion, warming of surface water temperatures and changes in wildlife populations, according to environmental experts.

"Hemlocks are not as key for timber, but they are huge for wildlife," Harmon said.

Environmental officials in southwest Michigan are already coping with HWA infestation sites, including exhaustive surveying and actual treatment with pesticides.

Sites with active HWA infestations are found along the Lake Michigan shorelines in Allegan, Muskegon, Oceana and Ottawa counties, according to the Michigan Department of Natural Resources.

The hope is the invasive pest insect can be halted, Menninga and Harmon agreed, but its appearance here remains a possibility. That's why they are out surveying this winter.

The Michigan Invasive Species Grant Program issued a grant to national nonprofit The Nature Conservancy. The program funds the work now underway in Benzie, Grand Traverse, Leelanau and Manistee counties among officials with the Northwest Michigan Invasive Species Network, as well as within the Charlevoix-Antrim-Kalkaska-Emmet Counties Cooperative Invasive Species Management Area.

A map of Michigan's areas infested with HWA can be found at online.

Editor's note: This story has been updated to correct information about a grant. The Michigan Invasive Species Grant Program issued a grant to The Nature Conservancy. — Feb. 12, 2019