Bringing natural holiday greenery into Maine or shipping it out of the state risks transporting invasive pests over state lines. Credit: Linda Coan O'Kresik / BDN

No one appreciates uninvited guests who crash holiday celebrations.

It’s annoying enough when it’s distant friends or relatives. But when it comes to what may be lurking in your festive decorations, it can be a disaster for native ecosystems.

That’s why the Maine Department of Agriculture, Conservation and Forestry is stressing to Christmas tree growers and wreath-makers the importance of preventing the movement of pests into and out of Maine on holiday decorations that contain plant material.

“Invasive insects, diseases and plants can easily be moved long distances on Christmas trees and wreaths,” said Gary Fish, state horticulturist with Maine DACF. “All of these pests can end up emerging on old wreaths or trees that are left out in the yard after the holidays.”

Branches and leaves from boxwood is a popular wreath material, especially for people who want the decoration to last beyond the holiday season. This year Maine DACF says it’s more important than ever to know the source of any boxwood greenery because it could contain box tree moths.

The moth is a new invasive that was first found two years ago in New York. It’s hard to detect and the caterpillars can kill the plant by rapidly stripping its leaves and girdling its stems.

In Maine, the winter-hardy boxwoods are popular landscaping plants, including in hedges.

Box tree moths overwinter as small caterpillars in a structure called a hibernaculum, which is made of a few leaves tied together by webbing. In this structure, caterpillars can easily hide and survive in any boxwood material, including live or cut plants and stems used in holiday decorations.

To keep the moths out of Maine, DACF wants you to stay away from any boxwood sources from Niagara and Orleans counties in New York; Clinton, Eaton, Ingham, Jackson, Lenawee, Livingston, Monroe, Oakland, Washtenaw and Wayne counties in Michigan; Hamilton and Clermont counties in Ohio; and all of Massachusetts.

If you are thinking of sending some Maine-made holiday decorations that have fresh plant or tree material, keep in mind that there are pests here that are not in other states.

“All of the states work together through the National Plant Board and USDA-APHIS (Animal Plant Health Inspection Service) to help prevent or slow the spread of invasive species that threaten plant health in all states, tribal lands or territories,” Fish said. “We observe quarantines that are adopted by each state.”

So before sending anything using living Maine vegetation, check it first for any insect activity and whether you are even allowed to ship it to the intended destination.

There is also a USDA federal quarantine in place for the spongy moth — formerly known as gypsy moth — active in Maine.

That means USDA certification is required to send any plant materials sourced in Maine — including live trees, cut trees, wreaths or cut branches grown outside of a greenhouse — to any state other than Delaware, Maryland, Massachusetts, Michigan, New York, Pennsylvania, Rhode Island or Vermont because they are already infested with the moth.

Certification is available from the Maine USDA-Plant Protection and Quarantine office.

Spongy moth caterpillars are invasive pests on many of Maine’s hardwood species including oak, apple, birch, poplar and willow. The caterpillar can devastate large areas of trees by defoliating them.

The moth overwinters as eggs laid in buff-colored masses resembling sponges on trees and other outdoor surfaces. That makes it easy for them to spread to other areas if egg-infested greenery is used to create holiday decorations.

A tiny but serious pest with piercing and sucking mouthparts has established itself along the southern Maine coast from York to Hancock counties.

The elongate hemlock scale bug uses those mouthparts to drink the fluid from the needles on hemlock, pine, fir, spruce, cedar, yew and juniper trees. This causes the needles to die and drop off.

Wisconsin now has a quarantine preventing elongate hemlock scales from getting into the state. To send any holiday decorations made from the affected trees in Maine, you need to contact officials in the state horticulture program at for possible export certification.

Being on the lookout for invasives is something that should be practiced year-round, Fish said.

“I think the holidays are significant, but less important than international commerce or people moving firewood around,” Fish said.

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.