Hubbard Fellowship Post – Kees Catches Lightning (Bugs) in a Bottle

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Today’s post is written (and illustrated) by Hubbard Fellow Kees Hood. Kees (pronounced “Case”) came to Nebraska from the Los Angeles, California area. He brought with him a strong interest in grasslands and an even stronger curiosity about the prairies east of the Rocky Mountains.

This past summer, whenever anyone has asked about the Hubbard Fellowship, I’ve inevitably found some reason to steer the conversation to fireflies. My home state of California lacks the mass firefly displays common east of the Rockies, instead being home to a diversity of cryptic flashless or solitary ground-flashing species. The first firefly at PRP began displaying June 12, a lone, blinking light outside my window. Within several weeks, this had built into a spectacular twilight performance, with thousands emerging at dusk to outshine the stars for a few brilliant hours.

I spent many midsummer nights out on the prairie watching fireflies, much to the delight of the local mosquito population. If you watch them carefully, you’ll quickly discover that there is more than one “firefly” – a fact that surprises most people I talk to. Male fireflies have distinctive flash patterns that can be used to differentiate species. Females, watching from the ground or nearby vegetation, pass judgment in a classic case of sexual selection. An adult firefly only has a few weeks to mate, so they must make every night count.

Male Photinus pyralis on some side oats grama. Photo by Kees Hood.

The show begins with the common eastern firefly, Photinus pyralis, that gives a burst of light while flying upward in a “J” motion, hence their nickname  – “big dippers”. They begin about 30 minutes after the sun goes down, when the sky is still fairly bright. Their displays build in intensity before fading out about an hour later. If you’re near a shrubby area, the smallest firefly on the Platte, Photinus curtatus, joins the show with little blinks every 3-5 seconds. It flies within and around shrubby thickets for a short 20-30 minutes before retiring for the night, making it easy to miss.

Photinus curtatus, the little gray firefly. Photo by Kees Hood.

The next act occurs on the edges of wetlands. Two species in the genus Photuris explode into a flashing symphony. One flashes every 2 seconds in a consistent, continuous pattern. The other looses 4-6 rapid flashes in quick succession, roughly every 5 seconds. Along wooded edges, ghostly, hovering lights become brighter over a few seconds before shutting off only to reappear several seconds later. The show becomes more difficult to follow. Hungry female Photuris imitate the females of other fireflies species, luring males to their death and using the extra nutrients for reproduction. By an hour and a half after sunset, the Photuris are at their peak, but the Photinus have begun to fade. The males that fly late into the night seem to fly increasingly erratically, confusing the novice firefly observer. The main show is over by midnight, but stragglers may continue until dawn on warm, humid nights.

Male Photuris firefly, species unknown. Photo by Kees Hood.
Fireflies at the Platte River Prairies on June 22, 2024. If the video link doesn’t work, click on the title of this post to open it online.

We know shockingly little about fireflies, especially in Nebraska. There are several reasons for this. They spend most of their 1-2 year lives as larvae living in leaf litter and soil. This makes them hard to find and almost impossible to study in the wild until they emerge as flashing adults. Many species(especially the genus Photuris) are remarkably hard to tell apart physically. A firefly expert who visited the Platte this past summer recommended against using physical features for the identification of Photuris.

Further complicating identification is the presence of many undescribed species – the riparian rapid flashing species found on the Platte, Niobrara, and Republican rivers potentially being one of them. Ranges for described species are poorly defined. A pinned specimen cannot preserve a flash pattern, and the limited number of firefly experts can only be in so many places at once. Firefly abundance and diversity decreases with aridity, and the Great Plains has received far less firefly research attention than the more speciose southeast.

Top view of another unidentified Photuris firefly showing off its dramatic coloration. Photo by Kees Hood.

There is a widespread perception among scientists and the public that fireflies have been on the decline, a trend that is both difficult to confirm and understand due to a lack of data. The factors implicated in insect declines generally- habitat loss, modern pesticide use, and light pollution – are probably contributing. Beyond these issues, we don’t really have a great idea why they’re declining or how to protect them.

The greatest diversity and density of fireflies are associated with wet meadows and riparian habitat along the Platte. At the Platte River Prairies they appear to be just as abundant in restored wet meadows and prairie as they are in remnant areas, suggesting that protecting and restoring these habitats is a good place for firefly conservation to start.

Fireflies are illustrative of what draws me, and I think many others, to the natural world. There is so much to know about any given species, so much we don’t know, and so much we may never know. Rabbit holes are everywhere in ecology, and you may fall into any given one for a lifetime and feel like you’ve barely scratched the surface.

Why Aren’t More People Talking About Migratory Flies??

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About a century ago, there were lots of reports of migrating insects along the East Coast of North America. Among those were numerous sightings of large, apparently migratory congregations of flies. And then, for reasons no one seems able to explain, there is nothing about North American fly migration in the scientific literature for almost 100 years.

WHAT HAVE WE BEEN DOING THAT’S MORE IMPORTANT THAN FOLLOWING UP ON REPORTS OF MIGRATORY FLIES??

It’s unconscionable, really. There are flies. Migrating long distances. And no one thought to go out and learn more about this?

Ok, that’s not fair. There’s been some great work in Europe on migratory flies (and other insects) – much of it in topographic locations like mountain passes where flying migrants of many kinds are funneled through narrow locations. They’ve documented numerous fly species, especially in the family Syrphidae (hover/drone flies), making seasonal flights in huge numbers. There’s still an awful lot to learn, but at least they’ve made a good start.

What’s especially frustrating is that some of those same migratory fly species are here in North America, too, along with many other close relatives. If they’re migratory in Europe, they’re almost surely migratory here, right? So why has no one checked?

Eristalis tenax, the common drone fly, appears to be a migratory species in both Europe and North America.

Well, after the long, inexplicable century of ignoring this fabulous field of research, there have finally been two recent North American studies (One in California and one in Illinois) on the topic. Both have confirmed that flies do still migrate on this continent, but we still know almost nothing about which species migrate, where they go, and why. Let’s fix this!

In the meantime, while we don’t know much about fly migration here in North America – and have huge knowledge gaps in Europe and elsewhere – we can at least marvel at it. First of all, as is the case with most migratory species on our continent, fly migration is probably a way to escape cold temperatures in the winter and then to spread out (and escape competition) when temperatures are moderate. Birds aren’t the only animals cool enough to do this, no matter what snooty ornithologists will tell you.

(I don’t mean to imply that all ornithologists are snooty. In fact, many are surprisingly decent and nice to talk to. If an ornithologist was snooty, though, they’d surely be braggy about bird migration, wouldn’t they?)

You might not think of flies as cold tolerant animals, but many can survive sub-freezing temperatures. Body size is one predictor of that (bigger flies can generally survive colder temperatures.)

It appears that within at least many fly species, part of a population migrates south for the winter and the other part doesn’t. This is common among other insect groups as well. It’s a good way to hedge bets. If the subpopulation that stays put is wiped out by a particularly nasty winter, the migratory party can return and keep the species going. Or, if the migrants all die during their perilous journey, the ones who stayed home will persist.

How does an individual fly know if it’s supposed to migrate or hunker down for the winter? GEE, WOULDN’T IT BE GREAT IF WE KNEW SOMETHING ABOUT THAT??

Generally speaking, the assumption is that fly migration is a multi-generational phenomenon. The flies that head south in the winter have babies that then start the northward migration the following spring. By summer, either those progeny or their offspring will return to where their parents/grandparents had been the previous year. Of course, we don’t really know that BECAUSE NO ONE IS PAYING ATTENTION.

Drone flies like this one resemble bees but have bigger eyes, short antennae, and only two wings instead of four. THEY ALSO MIGRATE.

I’d love to continue this incredible, compelling story and provide lots more details. Unfortunately, as you might have gathered by now, we scientists have largely wasted a century doing less important work than fly migration research. As a result, I’ll just stop here.

This drone fly is clearly staring at us in astonishment because we’ve not been curious enough to learn about its (surely) epic migratory activities.