Looking at Lichens
in a narrow range of habitat conditions. This makes them especially susceptible to habitat disruption. Many species are sensitive to air pollution, and lichens are used throughout the world to assess and monitor air quality. Despite these sensitivities, lichens are capable of growing in the harshest of natural environments. They live in fresh and salt water, deserts, tropical forests, alpine summits and even in Antarctica.
Because of the slow, uniform growth rates of lichens, scientists use some species of them in polar regions to establish the time and speed of glacial retreat. Some tropical lichens even grow on the shells of beetles and tortoises. In Missouri we have nearly 500 different species of lichens, including some found nowhere else in the world. Lichens are found in every square mile of the state, although in urban areas they are fewer, smaller and easily overlooked.
Lichens often contain bitter chemicals and are not a major wildlife food source, but they are an important component of the food chain. Land snails and many other small animals feed on lichens. In northern tundra, lichens are a staple winter food of caribou and reindeer. Locally, deer sometimes consume small quantities of lichens, especially in winter.
Several birds, including the ruby-throated hummingbird, eastern wood pewee, and blue-gray gnatcatcher, use lichens in nest construction. One of Missouri's most colorful warblers, the northern parula, prefers either old man's beard lichen (Usnea) or Spanish moss for its nest. Spanish moss is a flowering plant related to the pineapple and does not grow as far north as Missouri. Local populations of northern parula warblers often use the abundance of old man's beard lichens in healthy Ozark woodlands.
People have used lichens since antiquity as medicines, dyes, food, decoration, perfumes and even crude clothing. The subtle browns of Harris tweed fabric come from dyes made of lichens. Artisans in Europe have used lichens for centuries to produce a vivid purple dye. The acid sensitive litmus paper that many of us remember from high school chemistry classes also is made from lichen extracts. Some antibiotic salves also contain lichen extracts.
Although not poisonous, lichens generally are not palatable to humans, and some people have developed rashes from prolonged contact with certain lichens. People use a few species for food, especially during hard times, and the "manna from heaven" described in the Bible is thought by some people to be a desert lichen. In Asia, a large, saucer