migration | The Prairie Ecologist

The fall migration is in full swing through our prairies. Dragonflies, birds, butterflies, and more are moving southward. Going out on dewy mornings is a great way to check up on butterflies and dragonflies because I can find them immobile and covered in dew on their overnight roosts. This week was a big week for variegated meadowhawks (dragonflies), apparently. I found dozens of them at our family prairie one morning (more photos toward the end of this post).

Variegated meadowhawk at sunrise. Helzer family prairie.

There are lots of little brown birds skulking in the vegetation this week. Many of them are grassland sparrows of various species, but there also were a bunch of sedge wrens at our family prairie. Most of those birds are hard to see unless you flush them while walking through the prairie, but just standing still is also a good way to hear them as they rustle around in patches of tall grass. The sedge wrens made it easy because they not only rustled, they also called to each other with their machine gun songs (“Dot Dot d-d-d-d-d-d-d-d-d-d!”).

One of many sedge wrens hiding in the grass this week.

Monarchs are far from the only migratory butterfly (not to mention moths) coming through. I’ve seen a lot of painted lady butterflies this week and found a few orange sulphurs that (probably?) were on the move. There was a cluster of pearl crescent butterflies in our yard this week, too, but as far as I know, those aren’t migratory. They looked like they’d all recently emerged as adults, so they’d better hurry if they’re going to lay eggs before freezing temperatures hit!

As I see the abundance of flies still active at this time of year, I can’t help wondering how many of them are migrants. A year ago, I wrote a post complaining about the lack of North American research on migratory flies. I’m sure that spurred a flurry of activity among researchers (eye roll) and that we’ll soon know a lot more about the topic. In the meantime, I’m left to wonder, especially about all the different drone flies and hover flies I see. Are they just scrambling to eat (and lay eggs?) before frost? Or are they fueling up during a long southward journey?

A gorgeous dew-covered fly. Is it a migrant or resident? I don’t have any idea. Lincoln Creek Prairie.

Most insects, of course, don’t migrate, so they have to survive Nebraska winters however they can. That usually involves finding a sheltered place to hide and then just withstanding freezing conditions. Species vary in terms of whether they go through winter as adults, eggs, or larvae/nymphs. All of those options seem to work ok.

This katydid thought it was hiding from me on an early morning this week. I’m not sure whether this species lives through the winter as adults or eggs.

Male American bumblebee (*Bombus pensylvanicu*s) roosting on the underside of a tall thistle leaf.

A lot of the individual insects out and around now will simply die as winter hits. The only bumblebees, for example, that survive the winter are the fertilized females that will be next year’s queens. Everyone else in the colony will perish at the end of this season. Other insects that lay eggs before winter will also die after completing that task. I imagine that abundance of dead insects provides a big bonanza of food for any animals out poking around after the first big freeze or two. If not, bacteria, fungi, and other microorganisms will clean up the rest.

This caterpillar was literally hanging around on some big bluestem (remarkably camouflaged!) this week. I imagine it’ll spend much of the winter frozen solid, either as a caterpillar or pupa.

Plants are also shutting down for the year. Most wildflowers and grasses are finished blooming and have produced seeds if they can. Perennial prairie plants are also making buds. Woody plants make buds aboveground where new leaves or stems will emerge next year so the plants can continue to grow larger (assuming they don’t get burned, chewed, or cut down). Herbaceous plants, though, including grasses, wildflowers, and sedges, create buds at their bases, usually right below the surface of the soil.

Over the winter, the entire aboveground portion of perennial herbaceous plants dies back. In the spring, though, those plants will start a new season of growth from their basal buds. Seeds are still important for those perennials, though, both because it allows them to combine DNA with others of their species (cross-pollination) and because it lets them spread progeny into new places. Seed dispersal strategies are fascinating and beautiful, and it’s a fun time of year to see a lot of them in action.

Indiangrass seeds dangling from a seed head, ready to be carried off by a breeze or passing animal.

This milkweed seeds are poised to fly off in the wind once the sun dries the dew drops from them.

Late summer and early fall are great times for dewy mornings. Those water droplets are a boon for insect photographers, but they also make nice photo subjects on their own.

Dew drop hanging from a leaf after sunrise.

Back to the abundance of variegated meadowhawks this week… I can’t remember seeing so many at a time before, but that doesn’t mean much. I tried to quickly photograph a selection of those I found at our family prairie one morning, but I just kept finding more and more. Here are the ones I managed to photograph:

There was one dragonfly in particular that was perched attractively on top of some stiff goldenrod as the sun came up. I circled back to it a couple times as it started warming up and managed to photograph it from multiple angles while it was still too cold and wet to fly away. All the rest of the photos below are of that same individual.

I don’t know how much longer this late season flurry of activity will last, so I’m trying to catch as much of it as I can. I’ve gotten behind on some projects because I’m trying to see things before they’re gone, but I’ll have the whole winter to catch up, right?

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.

The Prairie Ecologist

Essays, photos, and discussion about prairie ecology, restoration, and management

Tag Archives: migration

Photos of the Week – October 10, 2025

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