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A spruce beetle, Dendroctonus rufipennis, is a very small beetle that digs into the bark of certain types of spruce trees. The species is native to North America with high concentrations found in Nova Scotia, British Columbia, Ontario and Quebec; it is also found in some northern areas of the US. Full grown spruce beetles are no more than 0.75 inches (0.64 cm) in length and are often hard to spot. Typically the way the presence of these pests is first known is by the serious damage caused to the trees they inhabit. Trees infested with these destructive insects frequently die.
The spruce beetle favors some types of spruce, including white and Sitka trees, but it tends to avoid the black spruce; on occasion it will infest them as well. It lives in the phloem, a relatively thin layer of actively growing wood. This layer is between the bark and the solid wood core of the tree. The spruce beetle kills many of the trees it infests, but because it does not dig deeper into the wood of the tree the wood can often be salvaged after the tree dies. All of the inner wood can typically be used commercially, as long as it is harvested within a reasonable time frame.
A large tree that is hosting a population of spruce beetles may have 100 or more of these insects for every square foot of bark. In the summer the spruce beetle will come out of an existing host tree and fly to other trees in the area. They typically live in dying or damaged trees, but if these are unavailable the spruce beetle will establish residence in any spruce it can find.
Human activity often encourages the spread of the spruce beetle. They can live in firewood and slash piles of debris left over from logging operations. When conditions are favorable, the insects will emerge from these places and find new homes in living trees elsewhere in the forest. Once established in an area, the pests can kill trees year after year, causing harm to both the trees and the economic stability of a region.
The spruce beetle causes a great deal of damage in areas that it infests. In the US, Alaska has lost millions of acres of forest, and in the 1990s Maine reported a loss of about 90% of the larger trees in some areas. People can help minimize the spread by not storing firewood for more than a year. Any cut wood should be de-barked, split, and dried to kill any spruce beetles that may be infesting it.