I write to you from Arapahoe, Ute, and Cheyenne land. I am interested in learning about the different animals that live in the place where I was born. Before we start with today’s animal, I want to emphasize that biological classification as understood by western society has its roots in racism, sexism, and transphobia – here’s a good explainer about why.
Coloradans who spend any amount of time in the mountains will have noticed large swaths of dead pine trees on our hillsides over the last decade or so. There are some areas where the dead trees seem to outnumber the living – Wolf Creek Pass, for example – and scientists this summer published research that increasing heat and drought are the main causes of this in Colorado. However, there are several species of beetle which also contribute to the death of our trees, and therefore an increase in fuel for forest fires. One notable species is the Fir Engraver Beetle (Scolytus ventralis), a relative of the spruce beetle and the mountain pine beetle (all usually called “bark beetles” colloquially). Each of these types of beetle uses the phloem, the inner bark of the tree that transports sugar throughout its body, as a nursery for their young. The Fir Engraver Beetle uses a number of tree species for this purpose throughout British Columbia, the western USA, and northern Mexico; the only tree they attack that grows in Colorado is the white fir (Abies concolor).
White firs’ natural habitat is the mountains of southern and central Colorado: the San Juans, the Sangre de Cristos, the southern end of the Sawatch range, and their most northerly population is on the southern flank of Pikes Peak. There are also a few non-native white firs in the Boulder area, which were planted by the Civilian Conservation Corps in the 1930s.
Unlike other bark beetles, the Fir Engraver Beetle only occupies a small area under the xylum (the woody exterior of the tree) that can lead to dead branches but otherwise will not affect a healthy tree. Unfortunately, for trees already stressed by heat and drought, or affected by root disease, even this small activity can be a death sentence. The life cycle of the beetle is usually just one year – emerging as a young beetle from inside of a tree around June and then beginning its mating cycle:
“Female beetles initiate attacks on random standing green trees, freshly cut logs, and recent wind throws. She bores into the tree’s bark and is followed by a male which she mates with. The female bores a horizontal gallery which radiates out on either side of a central nuptial chamber… The egg gallery may be anywhere from 4 to 12 inches (10-30 cm) long. During the 5 to 7 weeks after mating the female will lay between 100 and 300 eggs along the gallery. Four to six days after the female begins boring the egg gallery, a yellowish brown discoloration appears in the surrounding area. The stain is caused by the fungus Trichosporium symbioticum Wright, which is carried by the beetles.”
Unfortunately these beetles don’t have many predators and, although a prolonged deep freeze can kill them, usually the eggs survive under the insulation of deep snow. The main way to protect trees from them is to make sure the trees are healthy – so not stressed by heat or drought. Unfortunately things are not trending that way for the present, near, or distant future…