Thursday, June 11, 2009

LOOK FOR: Fireflies

One night many years ago I looked out over a field dancing with fireflies and I had a realization: this is why people believed in fairies.

fireflies in a jar by jemelah
Photo credit: jamelah
I must have been thinking of Disney's Tinkerbell and her trail of twinkling pixie dust, so much like the swooping, twinkling light of the fireflies. Or J.M. Barrie's description: "when the first baby laughed for the first time, its laugh broke into a thousand pieces, and they all went skipping about, and that was the beginning of fairies."

But those dancing lights aren't fairies. They aren't flies, either: they're beetles, actually. In the light of day, they look like nothing special: black beetles, sometimes with a red head. The exact looks of a firefly depends on the species; there are 23 genera and about 200 species of fireflies in North America.

fireflies mating
Mating fireflies by
The Natural Capital
The different species also have different flashing patterns at night. (The Museum of Science, Boston, has an animation that shows what to look for to tell the difference.) Some come out at dusk; others wait for more darkness. Some are high in the trees; others are closer to ground level. They also may flash different numbers of times, with different duration, and flying in different patterns while they flash. That way, they only seek mates of their own species. Unless, that is, they've been tricked by an impostor in the genus Photuris, which mimics the flashing patterns of other fireflies to lure them in and eat them.

When they're done mating, female fireflies lay their eggs in the ground or in rotting logs. The larva of a firefly looks like a grub, and eats other insects, as well as worms, snails and slugs. The larvae -- and the eggs -- can glow in the dark. This gives the family of fireflies their name: Lampyridae, from the Latin and Greek words for "glowworm." One theory is that the green glow is a warning sign to predators that these larvae don't taste good. Apparently, the adults don't taste good either.


Photo credit: James Jordan
But humans don't care what they taste like. And so we like the dancing green glow: as a sign of summer, as a memory of childhood. Or as a glimmer of hope that fairies really do exist, if we only believe.

In the wild: Different species like different habitats, but a good bet is to look at the edge between forest and open field. They also seem to like to be near a source of water. The picnic areas at Rock Creek Park are probably ideal.

In your yard: Even when we lived in a 6th floor condo in Dupont Circle, we could see fireflies in the street trees. But there are some things you can do to help attract and protect fireflies in your yard, if you have one:
  1. Habitat. Because they spend a lot of time on the ground during the day, fireflies may be harmed by lawn mowing. In addition, lawn pesticides aimed at grubs may kill firefly larvae, which also live in the soil. This is just one more reason it makes sense to avoid spraying your lawn, and let it grow to at least 3 inches before cutting. Better yet, consider replacing some lawn with plants that do not need to be mowed.
  2. Darkness. Some scientists think outdoor lights and streetlights may interfere with fireflies' ability to communicate and find mates. You may have a better show if you leave your outdoor light off.
  3. Research. The Museum of Science, Boston asks people to report their observations of fireflies once a week throughout the summer, to learn more about firefly distribution and behavior. Sign up at Firefly Watch.

Have you started seeing fireflies yet? Do you have a favorite place to watch them? Leave a comment.

6 comments:

Jamey said...

I recall while paddling on a NC river once after dusk, my eyes noticed a splattering of lights slowly dimming on and off in the muddy bank. However, when I turned on my flashlight I could not see anything but mud. Only after turning the light on and off several times could I find the well camouflaged gray segmented beetle grubs with the glowing rump. This was my first encounter with firefly larva... the glow-worms.

2 nights ago my daughter caught 5 fireflies in our yard and promptly placed the little fairies in a bottle by her bed... a ritual every year for the first night they appear. I can testify that we have more in our yard than in any other on our street... no doubt due to the fact that I put zero chemicals on the lawn and cut the grass only at gunpoint.

Elizabeth I recall reading as a kid that some fireflies females don't have wings, but to date I've never found a wingless one signaling back. I'm thinking maybe we don't have these species in our area. Any ideas Elizabeth?

mattandeliz said...

Good question. Poking around on the web I can find statements like "the females of many species are wingless," but not a lot of detail. In England they call the females glow-worms, so I suspect this is more common with European species than with the species that are common here. We'll have to keep an eye out...

WashingtonGardener said...

Saw my first of the season last weekend in my backyard -- my cat enjoys sitting in the screened-in sunroom and watching the nightly show at dusk too. Better than TV!

Colleen said...

My younger daughter (just turned 6) has spent most of the evenings this week catching fireflies, and even took them into school (with the container covered in a towel, so the fireflies would think it was nighttime.) My older daughter (almost 9) is horrified that she is killing them. (That UU principle to respect all life showing through :-) Do you think the fireflies can survive 18 or 20 hours of captivity?

mattandeliz said...

It's ok to keep fireflies for a day and let them go the next night. If you put a moist paper towel in their container it's supposed to help. It's probably also better to let them have normal light during the day so they don't get confused (but don't heat them up in direct sun).

The adults don't live very long, so if some die on your watch it's not necessarily your fault. But you do want them to be out in the world making the next generation of fireflies!

MarkNearRFK said...

Great blog, Elizabeth and Matt! I might just go on a mycological foray! And a buddy and I just noticed the fireflies in fair abundance in Rosedale two nights ago. Ciao!

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