Wednesday, April 7, 2010

Adirondack Insects: Fireflies, Firefly Larvae, and Glowworms

I was strolling along the other evening, headed back home from a trip to a vernal pool to check out the singing frogs, when my eye was caught by a small movement on the pavement. I stopped to take a closer look. What I saw was one of the strangest insect larvae I have ever encountered. It looked as though someone had crossed a caddisfly larva with a pangolin (those odd armored mammals from Africa and Southeast Asia). As it moved across the road, it would tuck its tail beneath it, kind of like a crayfish does when it wants to bolt. The head extended and contracted at the end of a long and rather telescopic neck. I stuck it in a vial and brought it home, hoping to identify it when I returned to the office.

It turns out that this odd-looking creature was a firefly larva. There are 20 genera of fireflies (family Lampyridae) in North America, with something like 150-200 species. So far I have been unable to identify which species my armored friend is, so I will have to be content with just knowing it is most likely in the genus Photinus or Photuris. The former are the small fireflies that blink around our yards on sultry summer evenings. Members of the genus Photuris, which are also in our yards, are slightly larger and harbor a deadly secret.

Well, perhaps that is a bit unfair, for it is only the females of Photuris that are deadly, and they are only deadly to any male Photinus who is so focused on finding a mate that he isn’t quite paying enough attention. Let me explain.

The blinking lights that fill our yards are secret codes. The males of each species are flashing specific patterns to attract females of the same species. When a female blinks back the right response, the male flies over for a little tête-à-tête (wink, wink; nudge, nudge). This is how little Lampyridae are made. Enter the female Photuris. She’s lurking in the yard waiting to trick a male Photinus her way. When she sees him blink, she blinks back with the code of a female Photinus (how she got the Photinus code book I don’t know). An unsuspecting male sweeps in, thinking he’s got a hot date, and she eats him. In all fairness, though, she does this for her offspring, for the defensive chemicals she absorbs from his body are used to protect her eggs.

Any article on fireflies (aka: lightning bugs) is bound to mention how it is that these insects (which are not flies or bugs; they are beetles) create light. It is a highly efficient chemical reaction, involving specialized cells: phytocytes and reflector cells. The phytocytes contain the necessary chemicals (oxygen, magnesium, luciferin and the catalyst luciferase), while the reflector cells intensify and direct the light. Air mixes with these chemicals and the reaction creates light, known in the scientific world as bioluminescence.

Not all fireflies create light, though. Some fireflies, like those belonging to the genus Ellychnia, are diurnal, and as such have no need to create light. After all, firefly light isn’t really all that bright (it just looks bright in the dark of night), so during the day it just wouldn’t show up. Therefore, it would be a total waste of energy for these diurnal species to produce it. However, just because the adults don’t glow, doesn’t mean the children don’t. In fact, as far as I’ve been able to find, all known species of firefly larvae (and some eggs) glow, which is probably why they are called glowworms, but this is a misnomer.

Technically, glowworms are insects from the family Phengodidae, which are related to fireflies. In this family, it is only the larvae and adult females that can make light. Phengodidae is a rare family in the northeast, so we aren’t likely to encounter them, which is a shame, because the larvae are militant predators of millipedes, and it would be interesting to see one in action.

And if that weren’t confusing enough, there is a species of fly larva that is bioluminescent (from the family Mycetophilidae), and it is also referred to as a glowworm.

But for us, here in the North Country, any natural object producing its own light at night is probably a firefly. And if it is on the ground, it is probably a firefly larva (although it could be a fungus known as foxfire…but that’s fodder for another article), out in search of food, such as snails, worms, or maybe even slugs. They are good to have around.

Traditionally, we don’t see fireflies up here in the mountains until about mid-June. It will be very interesting to see when the first blinkers show up this year, considering how early everything is appearing this spring. Firefly watching can be a great deal of fun, and if you watch the blinking patterns carefully, you might be able to discern which species is in your yard (the book Discover Nature at Sundown has an illustration of different firefly blinking patterns). Armed with a flashlight, you might even be able to attract a male firefly to your hand.

I want to leave you with one last thought. It seems that fireflies, like many other species, are declining. Development appears to be the culprit, which these last few years has been compounded with the fashion of putting solar walkway lights around one’s house. As mentioned above, firefly light isn’t really terribly bright. With all the lights that are on throughout the night in urban, suburban and even some rural areas, fireflies are having a difficult time seeing each other’s signals. If they are unable to find each other, they cannot breed. As a result, populations have dropped, in some places quite dramatically. Just something to think about if you are considering putting solar lights, or any other permanent outdoor lights, around your property.

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Ellen Rathbone

Ellen Rathbone is by her own admission a "certified nature nut." She began contributing to the Adirondack Almanack while living in Newcomb, when she was an environmental educator for the Adirondack Park Agency's Visitor Interpretive Centers for nearly ten years.

Ellen graduated from SUNY ESF in 1988 with a BS in forestry and biology and has worked as a naturalist in New York, New Jersey, and Vermont.

In 2010 her work took her to Michigan, where she currently resides and serves as Education Director of the Dahlem Conservancy just outside Jackson, Michigan.

She also writes her own blog about her Michigan adventures.


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