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Backyard Birder

From glowworms to fireflies, a world of lights

A few fireflies pulse their Morse code signals now, prelude to the big show a few weeks from now when meadows will sparkle in the dark. Count the pulses and you might be able to ID the species.

I have vague memories of catching fireflies when I was young. I don’t remember if we called them “lightning bug” or “firefly,” but catch one in a jar and you’ll see its true identity is beetle, not bug or fly.

When one becomes stranded between window screen and window, or all the way into a bedroom, their bioluminescence is impressive when the lights are turned off.

There’s a couple dozen firefly species in New England. To minimize courtship confusion, species have different flight times and fly at different heights. Each species has a preferred habitat — typically field, forest or marsh. Different species also have different color lights, from yellow to orange-yellow to a greenish tinge. A species’ unique pulse pattern is recognized by females perched below who flash once in response. The timing of the female’s flash — how soon it follows the male’s — is unique to each species.

Male and female continue their Morse code exchange as the male seeks the female’s location.

She lays her eggs on moist ground. The resulting larvae also produce light and often are called glowworms. That glow is thought to deter predators, as many firefly species contain chemicals repellent to predators.

Actually, the plot thickens. Female members of a genus lacking that chemical will flash a signal that lures males from species that have the repellent — and consume them. All the better to pass the chemical protection on to their offspring.

While the adult beetles live only a few weeks, the larval stage lives one or two years, depending on the species. Adults emerge in early summer and soon light up dewy fields and forests with the spectacular firefly display.

Fireflies have brought their periodic light shows to the world for some 20 million years before humans evolved. I suspect their displays were brighter than today’s, and more widespread.

For all the usual reasons — from pesticides to paved-over or disturbed habitat — firefly numbers have declined. In some urban areas they’ve disappeared entirely.

Streetlights, car headlights and residential lighting add further challenge, throwing off firefly pulse patterns and interfering with their visibility.

Often when wildlife species are threatened, the narrative turns to future medical advances that might be missed out on if a species goes extinct. Aspirin was derived from willow trees; horseshoe crab blood is used to detect contamination of vaccines and drugs administered intravenously.

Two chemicals that combine with oxygen to produce a firefly’s flash are increasingly used in medicine for bioluminescent imaging with a number of applications.

As one example, a healthy cell lights up when the chemicals are introduced but cells damaged by cancer or certain other diseases do not. Specialized cameras detect the presence of a tumor as well as its change in size over time.

The chemicals can be synthesized in a lab now, but the real thing can still be purchased. Live harvesting still goes on but to an unknown extent.

Meade Cadot at the Harris Center remembers collecting fireflies for a penny apiece when he was a boy. Adults could make a couple thousand dollars in a season.

I’m not a fan of the argument that species extinction should be avoided because of future medical applications yet to be discovered: “Save the Whales” because some whale extract will turn out to cure a deadly disease. That approach is exclusively human centered, a narrow focus that blinds us to larger issues.

However, if that argument works let’s use it to the max. A natural diversity of plants and animals needs all the advocates it can get, no matter the rationale.

There are firefly conservation efforts worldwide. Many people involved have sentimental reasons, not medical or ecological.

Nostalgia for the fireflies of youth motivates a lot of advocates for wild spaces and pesticide-free backyards.

As for the annual summer show, I wonder how many families have a tradition of waking up the young ones to witness the wonder of a sparkling, twinkling world coming soon to a field and forest edge not far from the backdoor.

It’s never too late. The younger the child the greater the magic.

Backyard Birder by Francie Von Mertens appears every other week in the Monadnock Ledger-Transcript.

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