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May 1998

Why Do Fireflies Glow?

Plus 24 other round-the-campfire brain stumpers every nature buff should know.

21. How can crickets tell the temperature, and what other creatures are weather forecasters?

The Weather Channel is more reliable than any critter, but the male snowy tree cricket (Oecanthus fultoni), found in all United States regions except the Southeast, does vary its chirping according to the temperature. Adding 40 to the number of chirps made in 15 seconds provides a close measure of the temperature in degrees Fahrenheit. Evidence is spotty for other creatures, but owls hooting throughout an autumn night are said to be harbingers of a storm, waterfowl usually fly higher in clear weather and lower in stormy weather, and woolly bear caterpillars are supposedly blacker before severe winters.

22. What do tree rings mean, and how do I count them?

In temperate zones, including North America, most trees add a ring every year, making a tree the only organism whose age can be precisely determined. Tree rings enable scientists called dendrochronologists to not only date specimens, but also “interpret how these trees have been treated by mother nature and human activity,” explains Dr. D.W. Larson, a professor of botany at Guelph University in Ontario, Canada. “Each of these long chronologies, as they are called, is a living clock whose ticks are louder or softer as a function of drought, cold, heat, and disturbance.” Certain tree species’ rings are easily identifiable, such as oak, ash, hickory, tamarack, fir, or northern white cedar. Each annual ring actually consists of two rings: a light-colored ring (earlywood) and a dark-colored ring (latewood).

23. Can snakes spit venom?

Yes, but thankfully not the ones in this hemisphere, Fellows says. The spitting cobras of Africa have a propensity for defending themselves by squirting a thin stream of venom toward the eyes of an attacker.

24. Why do leaves change color?

The green pigments known as chlorophyll, which capture energy from the sun, dissipate as the days grow shorter and the nights colder. This lets the yellow, brown, and orange pigments, called carotenoids, already present in the leaf shine through. Red and purple come from anthocyanin pigments, which are produced in sap cells beginning in late summer.

25. Do opossums really play dead or hang by their tails?

They’ll play “possum” when confronted by an aggressor and are known to secrete a foul-smelling substance like skunks do. As for hanging, young ones do but mature opossums are unable to support themselves by their tails, although they use them while climbing.

Matt Purdue hoards his Reese’s Pieces in the Southern California backcountry.

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