Christmas trees have the potential to spread unwanted critters

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This week:

Three years ago, an owl made headlines after being found in a Christmas tree that was about to be put up at 30 Rockefeller Plaza in New York City.

Trees provide habitat for wildlife, and that's a good thing. But it also means that Christmas trees can carry a variety of live cargo with them when they travel — and many aren't as harmless as "Rockefeller" the owl.

The Centre for Agricultural Biosciences International, a non-profit organization focused on science-based solutions for agriculture and the environment, lists the 12 pests of Christmas trees on its invasive species blog. The list includes the Western yellowjacket, a wasp native to western North America whose young queens spend the winter in species often exported as Christmas trees.

This has caused a huge problem in Hawaii, which imports about 90,000 Christmas trees a year, mostly from Oregon. At least two strains of the invasive Western yellowjacket are thought to have been introduced from imported live Christmas trees in the 20th century. 

The wasps are voracious predators that have eaten their way through local insect populations, competing with native birds and insects.

In order to reduce the importation of wasps and other critters, including garter snakes and slugs carrying the rat lungworm parasite, a certain proportion of trees imported to Hawaii are shaken, either mechanically or by hand, before shipping and after arrival. Infested trees may be sent back to the shipper, or "treated" with more shaking or hot water (to remove slugs).

Hawaii isn't the only place that imports Christmas trees and is concerned about hitchhikers.

Canada is a net Christmas tree exporter, but also imports some. In 2022, Canada exported 2.4 million trees worth $98 million, Agriculture Canada reports, mostly from Quebec, Nova Scotia and New Brunswick.

More than 95 per cent went to the U.S., but some also went to Panama, many Caribbean countries, Venezuela and the United Arab Emirates.

One pest of concern that can move between Canada and the U.S. via Christmas trees is the LDD or spongy moth, formerly called the gypsy moth. It can also be a concern with trees moving between different parts of Canada; it caused the shutdown of at least two Christmas tree lots in Thunder Bay, Ont., last year. 

According to the Canadian Food Inspection Agency, trees moving from "regulated" Canadian areas infested with the moth to non-infested U.S. areas need a "phytosanitary certificate" saying they've been inspected and have either been found free of moths or have been treated for it.