Tag Archives: life cycle

What’s behind a fabulous firefly season?

Sometimes our summer nights are ablaze with silent sparks, while other years we might barely see a flash in the exact same spot. What gives? A recent study provides some insight into what drives these fluctuations, and it reminds us to take the long view.

These flashy adults are the just reward for having survived many months during their larval stage.

Keep in mind that the flashy adult represents just a tiny fraction of a firefly’s life cycle. Before that, they spent up to two years living underground in a juvenile larval stage. During this time they are eating machines, growing steadily as long as they have access to their prey – mainly earthworms, snails, and slugs. Only if they manage to survive predators, competitors and climatic conditions will they eventually emerge into an adult firefly.

Fireflies spend many months being very cute in this larval stage

The study:

Firefly Watch observations gave info on firefly abundance across all species

What was their goal? Tracy Evans and her colleagues (see full citation below) decided to see if they could predict changes in adult firefly abundance across different U.S. locations using data on weather conditions during juvenile development.

What did they do? They took data gathered by citizen scientists who participated in Firefly Watch between 2008 and 2016 (only total firefly counts were used in this study). They combined this with information from NOAA on monthly temperature, precipitation (rain & snowfall) and soil moisture for each location.

Weather conditions before adult emergence had an impact on firefly abundance.

What did they discover? Weather conditions during juvenile development had a small but significant effect on the abundance of adult fireflies. In particular, adult abundance increased when soil moisture was high during development, and decreased when soil moisture was low. Precipitation also mattered: for 20 months before adult emergence, both too much and too little precipitation reduced firefly abundance. Very high maximum temperatures during the previous winter and spring reduced abundance.

What does this mean? Of course different firefly species will have different requirements, but this study reveals some interesting general patterns. Fireflies seem to thrive when there’s sufficient soil moisture, and when there’s just enough precipitation – not too much and not too little during their juvenile stages.

Citation (warning, paywall!): Evans, Tracy R. ; Salvatore, Donald ; Van De Pol, Martijn ; Musters, C. J. M. 2019. Adult firefly abundance is linked to weather during the larval stage in the previous year. Ecological Entomology, 44: 265-273.

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Pyractomena Strangeness #3

“Tis strange – but true; for truth is always strange. Stranger than fiction.”

                               – Lord Byron, Don Juan (1823)

The previous episode left our Pyractomena larva hanging  – literally – doing some aerial pupation, very unusual behavior for a firefly! Forsaking the amphibious wanderings of its snail-eating childhood, the pupa now hangs quietly. But inside, a maelstrom of cellular reorganization and growth is transforming its larval body. In just a few weeks, it will emerge as an adult firefly. At this next stage, our Pyractomena will have only one thing on its mind: sex. And yup – you guessed it: Pyractomena fireflies have strange sexual habits, too!

Most male lightningbugs fly & flash to win females. But after racing to emerge early, Pyractomena borealis males forcibly mate with their child brides! Continue reading

Pyractomena Strangeness #2

We’ve already heard (previous post) about the weird hunting habits of Pyractomena larvae – they’re amphibious.  So let’s continue our Pyractomena tour, moving along to consider another strange behavior: they pupate en plein air!

Once they’re ready to metamorphose into adult fireflies, the larvae of most North American lightningbugs seek safety underground. Immobile, they huddle for weeks in soil chambers, finally emerging to light up our skies as adult fireflies. But no cold dark cellars for Pyractomena fireflies! Instead, these strange fireflies climb up onto vegetation to undertake a feat known as aerial pupation.

Pyr borealis pupation

Aerial pupation (photos from Faust 2012)

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Stranger Things – The Firefly Version

If you’ve been paying some attention, you probably already know that here in North America, we’ve got several different kinds of lightningbug fireflies. Those in the genera Photinus and Photuris are common and relatively well-studied. But the Pyractomena lightningbugs –  also pretty common – are a black box. We know so little about them! And more’s the pity because Pyractomena have a pretty bizarre lifestyle, making them quite a bit different from our other fireflies.

NAmerican Lightningbugs

Three North American lightningbugs, belonging to Photinus, Photuris & Pyractomena( L to R)

So here’s the first taste of Pyractomena strangeness: these amphibious larvae are snail-eaters! Continue reading

Next up: Fall glow-worm extravaganza

Autumn happens to be quite an exciting time for fireflies. I get it – you probably can’t imagine fireflies beyond summer.  And that is when adult get all reproductive and stuff. But there’s cryptic chapter in the firefly’s life story, and it’s starting right now.

Firefly Life Cycle.png

Once mated, the female firefly will produce 30-100 eggs, laying them one-by-one in some moist dirt or moss. After a few weeks, these eggs hatch out into tiny larvae that immediately burrow down underground. Though adult fireflies only live a few weeks, their progeny will spend up to two years hanging out underground.

Larval Jaws

photo by Melvyn Yeo (Flickr)

Baby fireflies happen to be voracious predators. They’re constantly on the hunt for earthworms, snails, and any other soft-bodied prey. They attack creatures that are much bigger than themselves. How do they manage this? First, they use their sharp, sickle-shaped jaws to inject the prey with paralyzing neurotoxins. Next, they secrete digestive enzymes to liquify their prey, then they slurp it up. Earthworm smoothie, anyone?

When they’re disturbed, larval fireflies glow from two tiny lanterns located at the tip of their abdomen. All firefly larvae can light up, across 2000+ species, even when the corresponding adults cannot. So we think fireflies’ light-producing talent first evolved because it gave these juveniles some advantage.

But … what’s the point of these juveniles being so conspicuous?

We know that fireflies contain nasty-tasting chemicals that help them avoid getting eaten (see earlier post). Lots of poisonous creatures use bright coloration to warn off potential predators. Yet firefly larvae are mainly active at night or underground, where having bright colors would be futile. But a flash in the darkness would certainly do the trick – like a neon sign, it  blazes out “I’m toxic – stay away!”

So get ready to watch for firefly larvae crawling along roadsides and wooded paths, glowing dimly. Often overlooked, these juveniles should rightly be celebrated as the original inventors of fireflies’ magical lights.

pageofbats life cycle illustration

Illustration by pageofbats (Flickr)

What’s good firefly habitat?

People often ask me this excellent question. Yet it doesn’t have a quick or easy answer. One reason is that different species live in different habitats. For instance, the salt marsh firefly Micronaspis floridana is restricted to intertidal regions along the Florida coast.  Another reason is that certain things matter to adult fireflies, whereas different things matter to the juveniles.

Micronaspis floridana

Some species have specialized habitat requirements (photo by Drew Fulton)

For adult fireflies, what’s most important is finding a dark place for their courtship displays. Artificial lights – streetlamps, outdoor security lights, even car headlights – can disrupt firefly courtship conversations.  Such bright backgrounds make it difficult for fireflies to see each other’s courtship signals. Another desirable habitat feature for adult females is easy access to suitable egg-laying sites, like moss, moist soil, or decaying wood.

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Texas Glimpses Some Late-Season Wonder

In most years, Texas fireflies have largely faded out by August. But this year, a second wave of fireflies has washed across central Texas during mid-September. What’s going on?

Last spring, warm & wet weather conditions produced a bumper crop of emerging adult fireflies (reported here). And similar weather conditions this fall have apparently created a repeat performance (reported here & tweets below).

fireflies-texas-sept-tweets

Sept 2016 sparked a firefly Twitterstorm from Austin

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