SEATTLE, Wash. — U.S. Customs and Border Protection continually inspects loads of firewood heading from Canada to the U.S. to prevent the entry of unwanted guests – the six-legged variety.

Despite ongoing inspection efforts, the threat of invasive species hitchhiking in wood shipments across the border remains. Effective Dec. 15 for commercial shipments (and Jan. 1, 2009 for noncommercial or personal shipments), hardwood firewood must be accompanied by either a treatment certificate or a treatment label certifying that the wood was heat treated to a core temperature of 71.1º Celsius for 75 minutes.

Without this proof of treatment, travelers will be turned back to Canada to dispose of their hardwood firewood. Hardwoods generally include: oak, beech, ash, maple, cherry and certain other varieties.

Softwood firewood, such as pine, may enter without treatment but it must be free of pests. It must also have written certification, which varies according to the type of wood and origin. If inspection at the border reveals plant pests, or if certification is lacking, travelers may have to take the firewood back to Canada.