Whirligig beetles still swimming in the bay
As we begin the delightful autumn month of October, it's good to take a look back at September. Though not always so apparent, the month was warmer and wetter than usual. Thanks to the earlier days, some in the 80s, we had a temperature that averaged several degrees above normal and only a few times did the mercury drop below 40 degrees. Perhaps the biggest weather factor of this month was the rain, sometimes quite hard, that gave us close to 3 inches above the norm. But looking back on these days of this season-changing month, I'm struck by the fact that for most of us, there was little-to-no frost.
Shorter days and cooling temperatures seem to go together as we get into autumn. During October, it is not unusual to experience frosts and maybe even some light snow. Along with the many other happenings of this month — colorful leaves dropping, more bird migration and "bright blue weather" — we also see the beginning of ice formation. Ice first forms on puddles or containers left outside. Thawing and melting later, the ice may next be found in small ponds or shallow swamps. Often by the end of October, ponds will hold an ice coating, even though it may be temporary. Larger bodies of water follow this lead later in the season.
It is during October that we'll see more of a response to the coming cold. We usually look for these changes with larger animals, but it happens with insects as well. Mostly we think of migration with birds and some mammals such as bats, but it also happens with some insects such as monarch butterflies and green darner dragonflies. Both of these insects have been apparent with their fall flights this year.
Many other insects will hibernate. This is seen in the anglewing butterflies: mourning cloak, comma and tortoise-shells. And ladybugs combine these two. They migrate to a safe location, often near the lake, and go beneath debris to hibernate.
But the bulk of insects will die as the cold moves in. Grasshoppers, crickets, most dragonflies and mosquitoes still about on these fall days will lay eggs and then succumb to the cold. Protected in soil or water, many of the eggs will hatch next spring. And there are those insects that keep active as long as they can with the cold moving in.
Each visit to a lake or pond in recent weeks has revealed an abundance of movement of tiny insects out on the surface of the water. Most aquatic insects live under water, often maturing to take up a terrestrial life as an adult. But these insects remain on the surface. Anyone going to a lake in summer is likely to see the skating of water striders on the surface and maybe even a large fishing spider moving here as well.
Further out in the water is often a large gathering of small dark oval-shaped beetles swimming, frequently in circles. When we get close they go into a panic-type of swimming motion, looking like they all are confused. This is their defense, making them harder to see and catch. When the danger is past, they settle and resume a normal life.
These floating mobile insects are called whirligig beetles. They've been with us since earlier in the summer. The rafts have grown and now may be made up of hundreds of individuals.
A closer look reveals that they are a marvel of adaptation to life in this zone. While most swimming insects have large hind legs for quick movements, the whirligig beetles have extended front legs, allowing them to do this whirling circling motion that we usually see. Also unique are their eyes that are divided so they are able to see above and below simultaneously.
These gregarious beetles are predators, feeding and traveling at night, sometimes moving long distances on the lakes. They may be in a bay one day, but not the next and then return later.
As I look at these surface beetles on this day in October, I note their movements and obvious territorial sites on the water, but I also wonder what will become of them when the weather gets colder and the bay begins to freeze.
The answer was seen on a previous trip during another year when I found the whirligigs still on the water as ice formed nearby. Looking closer, I also saw some on the shore. Apparently, these aquatic insects will stay as long as they can in the water, but then go on shore to go beneath the leaves and snow to hibernate for the winter. I enjoyed watching them in late summer and fall and I look forward to seeing this gyro motion on the water again next year.
Retired teacher Larry Weber is the author of several books, including “Butterflies of the North Woods,” “Spiders of the North Woods” and “Webwood.” Contact him c/o firstname.lastname@example.org.