By Kate Crowley
After giving a talk in Appleton, Wisconsin last night, we drove home, arriving around 3 a.m. Not our preferred time to be driving, but there was one unexpected bonus. After brushing my teeth and turning off the light in the bathroom, I thought I saw a tiny light outside the window, in the backyard. I pressed my face to the glass and there it was again: A firefly (or lightning bug to some) somewhere in the branches of the red pine. I watched it flash a few times and then it stopped. Yes, this is truly summertime, when the fireflies dance through the air.
I feel fortunate whenever we see these light producing insects (in the family known as Lampyridae, which comes from the Greek meaning “to shine”) in our fields because they have been declining over the decades where they have lost habitat to urban and suburban development. Many people over the age of 50 have strong memories of summer evenings spent chasing and catching the flashing beetles in canning jars and then keeping them overnight as bedside night lights.
I’m happy to report that three of my grandchildren got to experience a firefly evening when they lived in a small town in Ohio. There is magic in these tiny creatures; a magic that captures people of all ages.
In Minnesota there are at least 12 different species of fireflies, but a real aficionado could spend a life time trying to see all 2000+ species that exist in the world. They are found on all the continents, except Antarctica. It is usually around mid-June when they begin to appear and they peak around the 4th of July.
Glowworms are another light producing phenomena, but they are just the larvae of the fireflies. Producers of their own soft light, they also produce a poison which they inject into prey (snails, earthworms, and other invertebrates) which transforms into an easily digested meal for the larvae. They will then overwinter in the soil and in the spring transform into a pupa. Like a caterpillar in its chrysalis, fantastic changes occur and what emerges three or four weeks later is an adult firefly. Like all other insects its body consists of a head, antennae, thorax and abdomen, but here the similarities end – at the tail end of the insect. Appropriately called a lantern, this special organ contains cells with two chemicals called luciferase and luciferin. When these chemicals combine, and oxygen is added, as well as a molecule called ATP, light is created without heat. The oxygen comes through tiny holes in the abdomen and can be controlled, which in turns controls the blinking of the light.
All this blinking and flashing is part of the evolutionary trajectory for continuation of the species. Among most North American species of fireflies, it is the male who first flashes a signal with a specific color and timing to let females of his own kind know where he is. Females, who are generally clinging to leaves of one sort or another, will respond with a flash of their own. In this way they find one another and mate.
The two most common types of firefly in Minnesota are Photinus and Photuris. The former produces a yellow flash, usually right after sunset. The latter gives off a greenish or greenish-yellow glow and is more commonly found later in the night.
I have just looked out the windows this evening and it is nearing midnight. After staring into the darkened front yard for some time, I spot a faint flash. It almost seems as though my eyes are tricking me, but then I see another and another. Some are seen in my peripheral vision. All look yellow to me, but they show for such a brief moment, it’s hard to really determine their color. Still, they are out there and I am happy.
There is a special citizen science program called Fire Fly Watch (www.mos.org/fireflywatch). Based out of the Museum of Science in Boston, it is a national effort to learn more about the fireflies and their current populations. It takes very little effort and the results could turn out to be very useful to science and these special creatures. To make it even better, find a child to look with you and introduce them to these flashing fairies of summer.