For many locations in the Adirondacks, the growing season ended last week when the temperature dropped into the mid-20’s. The hard frost that formed on unprotected garden vegetables and cultivated flowers that were not covered was enough to destroy these sensitive forms of vegetation, along with many herbaceous plants that thrive in fields and meadows.
However, not all places in the region experienced freezing temperatures, as the calm air that permitted heat to be radiated from the atmosphere into space also allowed many spots to retain just enough warmth to stay several degrees above 32. In heavily wooded areas, the dense canopy of leaves that still exists is able to act like a sheet of plastic placed over a garden and trap the warmth of the ground beneath it.
The thermometer at my house, which is positioned about a dozen feet into a wooded setting, recorded a minimum temperature of 35 degrees on the morning when my entire lawn was coated with a very noticeably layer of frost. (I do periodically check the calibration of this device to verify that it is working correctly, so I am certain that the 35 degree reading was accurate for this specific location.)
Since exposure to freezing temperatures is lethal to many bugs, once the air begins to cool significantly, a number of these invertebrates temporarily retreat from an open area to the shelter of a wooded spot in order to escape the cold. This is one of the main reasons why many bugs continue to be encountered in the days following a killing frost. Mosquitoes, midges and moths are all likely to be noticed in the coming weeks despite the inability of various species of these flying insects to survive the freezing temperatures that have already been recorded throughout the region on several early mornings this season.
A mass of cold air, accompanied by a strong pressure gradient, occasionally causes a breeze at night which flushes the warm air from protected pockets beneath the canopy. During these cold snaps, the temperature in deciduous woodlands can plunge to near the same levels as those occurring in more open places. Bugs that sought refuge among the twigs and lower foliage of the underbrush during these early autumn events eventually perish, as they would if they remained in the open.
After the leaves have fallen in another several weeks, this shelter will be lost to those invertebrates that remain active into the early autumn. A hardwood forest from the middle of October through early May is nearly thermally identical to open areas that experience a rapid rate of cooling on clear, calm nights.
Bugs that spend much of their lives in nooks and crannies are able to continue to function longer into the autumn than those that fly. Crickets, earwigs, centipedes and millipedes all concentrate a significant portion of their time in places that are protected from the first few cold snaps of the season. Eventually, even these locations experience freezing temperatures as the cold becomes more intense, and they also perish.
Over the course of the next several months, our region will experience ever increasing cold spells. As the layer of leaves falls to the ground, and then as the moisture in the soil starts to freeze, no place will remain for bugs to escape the cold. This is why all of these organisms have evolved a dormant stage in their life cycle in which to pass the coming season. When a creature enters into an inactive state, its chemical composition is able to change to allow it to withstand temperatures that regularly drop below the freezing mark. Despite the periods of sub-zero weather that our region experiences in winter, most bugs, like mosquitoes, remain alive in a state of dormancy.
Just because we have had several mornings when a hard freeze has killed everything in the garden except carrots and pumpkins, it does not mean that all our bugs have been destroyed. While a few have died in this initial blast of cold air, it takes numerous such events, especially after the leaves drop from the trees to do away with this segment of our fauna, which always returns the following spring after the leaves emerge from their buds to again provide shelter from the drastic changes in temperatures here in the Adirondacks.