Something Blue

One of the most striking plants in our prairies this time of year is pitcher sage, also known as blue sage (Salvia azurea).  It’s tall, of course, but more importantly, as the surrounding prairie is dominated by green-becoming-gold grasses and big yellow flowers, pitcher sage stands out simply because it is starkly and unabashedly blue.

A few weeks ago, I posted a photo of a bee that specializes on pitcher sage, but there are many more insects commonly seen on the plant.  Last week, I spent about 45 minutes in our Platte River Prairies, photographing pitcher sage and as many visitors as I could.

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I initially pulled my camera out because there were several monarch butterflies flitting around a patch of pitcher sage.  While chasing them around (and, as always, being thankful no one was watching me), I came across quite a few other insects – some of which I managed to photograph.

A sulphur butterfly (and a second partially shown at the bottom left) enjoys pitcher sage.
Anthophora walshii (a digger bee) is a species I see on pitcher sage frequently, and this was just one of several hanging around a single patch of flowers.
This moth was nose deep.
Several skipper butterflies were around, including this sachem skipper.
Not all the insects were feeding on pollen and nectar.  I’m not sure what this plant bug was doing, but there it was.
This blister beetle was feeding on the flower itself.
This monarch was so distracted by the nectar of pitcher sage, I took this photo from about a foot away with a wide angle lens.
One more monarch…

In addition to being tall, striking, and beautiful, pitcher sage is also pretty good at withstanding drought.  During late August of 2012 – a year of extreme drought, pitcher sage stood out against a background of brown dormant grass, blooming just like it does every year.  Not only did it provide some welcome color when many other plants were wilting, it gave all the insects pictured above, and many others, something to eat when they needed it most.

What a great plant!

Photo of the Week – July 13, 2018

You know how you can look at something for years and still not see every aspect of it?  I was walking through Lincoln Creek Prairie this week, stretching my legs after photographing for my square meter project, when I came upon a couple big patches of Illinois tick clover (Desmodium illinoense).  There weren’t any active flowers on the plants, and I was about ready to move on after just a quick glance when I spotted something white along one of the stems.  Upon a closer look, I could see it was a moth, and it seemed to be plastered up against the plant.

This white moth seemed to be stuck on the stem of this Illinois tick clover plant.

As I inspected the moth more closely, it was clearly dead, and appeared to be essentially glued to the stem.

Here is the same moth, photographed from a different angle. Here you can see the abdomen stuck to the stem, and the mess it apparently made as it struggled to escape.

Now, I’ve known that tick clover plants (and especially their seeds) can be sticky, but I always ascribed that to the tiny stiff (and sometimes hooked) hairs covering them.  I sure wouldn’t have thought those hairs could catch and hold an insect.  However, as I looked more closely at the hairs on this plant, there were little tiny droplets of clear sticky fluid at the tip of each hair.  How can I have spent 25 years or more looking at prairie plants and not noticed that?  I looked online and in my copy of the Flora of Nebraska book and didn’t find any reference to those droplets in either place, but surely other people know of this.  I’ll have to look harder.  In the meantime…

…as I looked at nearby plants, I saw lots more dead or dying insects glued to them.  The most common of those were lightning bugs, followed by Japanese beetles.

Lightning bugs were the most abundant of the insects I found stuck to tick clover stems. I must have seen at least 20 within a few minutes.
Japanese beetles (invasive species) were also a common victim of the sticky tick clover plants. This one appeared to have become stuck on a leaf, so I guess it’s not just the stems that have adhesive qualities.

I’ve written before about insects getting stuck to the bracts beneath thistle flowers and discussed the possibility that the sticky bracts helped keep ants and other non-flying nectar thieves from stealing floral resources.  Do tick clovers do the same thing?  If so, why haven’t I noticed?

This little gnat (midge? something else? I can’t see the antennae) was the smallest insect victim I found.  If you click on this photo you can zoom in and see the droplets on the tips of the hairs.
This mosquito lost its life when it apparently tried to take a rest break on this tick clover plant.
This picture-winged fly was still struggling when I found it.

I’m really curious to know if others have noticed insects losing their lives to tick clover plants, and whether or not it happens with other Desmodium species.  Does the plant produce the sticky droplets of liquid throughout its growth period, or just when it is flowering?  WHAT IS GOING ON HERE?

Thanks for any help.

Re-emerging into the Warm Sunshine

On Monday, I took advantage of very pleasant weather to visit one of our Platte River Prairies I hadn’t seen for a while. The warm sunny day felt great to me, but apparently also invigorated a lot of other creatures. Wild turkeys were in full display mode, with males showing off to each other and to nearby females, and I flushed a prairie chicken from near where it and others had been lekking earlier in the day.

More interestingly, I saw all kinds of insect activity. Big green darner dragonflies were zipping around wetlands adjacent to the river, and nearby patches of bare sand were full of small hordes of brightly colored tiger beetles chasing after flies and other tiny insects.  I wondered whether the adult insects I was seeing had spent the winter as adults, and if so, how.  Green darner dragonflies are migratory, so the ones I saw might have moved back north from wherever they go during the winter.  I’m pretty sure the tiger beetles I saw had spent the winter as adults, sheltered in their burrows.

I’m pretty sure this is the bronze tiger beetle (Cicindela repanda) because it fits both the visual description and the habitat (bare moist sand near the river). This was the most common tiger beetle I saw.
There many fewer festive tiger beetles (Cicindela scutellaria), but they were certainly the most colorful.

As I was crawling through the sand on my belly, trying to get close enough to photograph tiger beetles, I occasionally flushed band-winged grasshoppers that were hanging around on the same patches of bare ground.  I managed to photograph both green and brown ones, which I assumed were different species until I got home and looked more closely at the photographs.  Despite the different colors, the patterns and textures of the grasshoppers looked identical to each other, so I sent the photos to a couple friends who have shown themselves willing to put up with my grasshopper questions in the past.

The brown form of the greenstriped grasshopper was much more common (and harder to see against the mostly still brown grass) in the prairies this week.

Both Ellen Welti and Angela Laws responded and let me know that both the green and brown grasshoppers were greenstriped grasshoppers (Chortophaga viridifasciata).  Greenstriped grasshoppers are band-winged grasshoppers, which are known for their colorful wings and their habitat of crepitation (loud snapping noise) as they are flushed and fly away.  Band-wings also tend to hang out in areas of bare ground, which matches where I found them this week.

The greenstripped grasshopper is very common and abundant in the eastern United States, but it is found in much more scattered populations out here in the west where it tends to be tied to areas of moist soil. The grasshoppers hatch from eggs in mid-summer and then overwinter as late stage nymphs.  Once they emerge in the spring, they molt into their adult form. During the winter they are in diapause (a kind of dormant state) that is apparently broken in the spring, not by temperature, but by increased photoperiod (daylength).  All of this means that greenstriped grasshoppers have to be extremely cold tolerant.  They have to survive the winter, of course, but even after they emerge in the spring they still have to face the kinds of spring cold snaps we’ve been dealing with this year.  During those cold periods, the grasshoppers find a place where they can nestle into some prairie thatch until temperatures rise again.  Then they bask in the sun until they’re warm enough to resume their regular activities.

In its green form, the greenstriped grasshopper is sure handsome, isn’t it?

Ellen shared a great anecdote about how cold tolerant the greenstriped grasshopper can be.  While doing grasshopper research at Konza Prairie (near Manhattan, KS), she put a batch of caught grasshoppers in the freezer – a standard way to kill insects before sorting, identifying, and pinning them.  Three days later, when she brought the bag of frozen insects out to work through them, a greenstriped grasshopper started kicking its legs!  Ellen said she felt bad for the grasshopper and ended up taking it back out to the prairie, where it seemed to be completely unphased by the whole experience and hopped back into the grass.

Seeing how quickly insect activity resumes after cold snaps during the spring is a great reminder of how resilient and well-adapted those creatures are.  We complain about having to put up with wild temperature swings, but we’ve got cozy homes and appropriate clothing to help us cope.  Birds, insects, and other animals don’t have the advantages we have – they’re just tougher than we are.  While not all of them can stand being frozen solid like the greenstriped grasshopper (though many of them can), they have been dealing with crazy weather events for many thousands of years, and will likely continue to do so in the distant future.  I bet they whine a lot less about it too.

Pollinators and Insect Conservation Field Day – August 5

Here are some more details on our upcoming field day at the Platte River Prairies on Saturday August 5.  The day will run from 9 am to 2 pm and will focus on pollinators and other invertebrates.  We’ll talk about ecology and natural history of invertebrates, but also about invertebrate-friendly strategies for prairie restoration and management.  The format will all be field-based, so our presenters will be talking as they lead hikes around the prairie.

The gray hairstreak butterfly is just one of many insects we should see on August 5. Did you also notice the little beetle next to it? Come learn about both the easily visible and more hidden aspects of the invertebrate world!

Jennifer Hopwood of the Xerces Society will be on hand to talk about pollinator insect ecology and conservation issues.  Julie Peterson, with University of Nebraska extension will be talking about other invertebrates.  They’re both really engaging and have strong expertise, so be ready to see (and catch!) some insects and learn all kinds of new information.

In addition, Sarah Bailey of Prairie Plains Resource Institute (PPRI) will be leading tours of our restored prairies and talking about restoration methods that favor pollinators and other invertebrates.  Sarah and PPRI have restored well over 10,000 acres of prairie in eastern Nebraska in recent years with high diversity native seed mixtures.  I will also be leading tours and talking about how to use fire and grazing management to sustain strong and diverse invertebrate/pollinator populations.

The field day is free and open to the public, and should be useful to nature enthusiasts and their families, as well as conservation professionals.  You can come anytime between 9 and 2 and join in with whatever tours are going on.  Bring your own lunch and water bottles, but we’ll provide snacks and cold drinks as well.  Be sure to bring along whatever other field supplies you need – sunscreen, hat, insect repellant, etc.

The prairies should be putting on a good show – we’ve had some recent rains and the wildflowers and insects are having a really good year.  I hope to see you there!

Location: The Nature Conservancy’s Derr House.  Take the Wood River Exit (#300) off Interstate 80 and head south for two miles.  When the highway curves sharply to the east, take the gravel road that allows you to continue south and you’ll immediately see the TNC sign and big brick Derr House on your right.  Parking is at the bottom of the hill before you get to the house.

Hubbard Fellowship Blog- Marvels in the Mud

This post was written by Evan Barrientos, one of our Hubbard Fellows.  Evan is a talented writer and photographer and I encourage you to check out his personal blog. If you would like to see more of his photographs, you can follow him on Facebook.

April 2nd was the kind of spring day where you triumphantly open every window in the house. I wanted to get out and explore somewhere new, so I drove to the Fort Kearny Hike and Bike Trail. When I arrived, a bored-looking family was slowly rolling down the weedy trail…in a golf cart. I despaired, thinking that I had driven half an hour to look at weeds with joggers huffing by. Nonetheless, I walked down the crowded trail for a couple of uneventful minutes minutes until it crossed over the Platte River. Much to my relief, there was a staircase inviting visitors to explore the sandbar below. I descended the stairs and started exploring the one place no one else was. It would be another three hours until I returned.

I began by walking in the thicker vegetation, hoping to flush some of the first insects of the year. As I did, several small spiders scurried away. I knelt down to look at them and noticed a few gnats mating on the blades of grass. After a long winter with no insects, these gnats were as exciting for me to photograph as Sandhill Cranes.

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Once I was on my belly, more details revealed themselves and a story began to unfold. A few feet from the gnats I spotted a muscid fly. I’m grateful that winter had made me so appreciative of even the common insects; otherwise I might not have taken a closer look. I did, however, and noticed that this wasn’t your typical potato salad-sucking housefly. It was devouring one of the gnats!

The calls of sandpipers drew my attention away from the microcarnage and I went over to the open part of the sandbar. There, I found a migratory flock of Baird’s Sandpipers foraging in the mud. I sat and watched them, wondering how they could possibly find enough food in the muck to sustain their 3,700-mile migration from Argentina. When they flew away, I thought I’d try to figure it out. A tiger beetle distracted me and I started stalking the speedy predator on my belly. Each time I would crawl close enough for a decent photo he would dart a few inches ahead. For several minutes this continued until he had led me to the muddy edge of the sandbar. There, with my nose inches away, it dawned on me how much amazing life that mud contained.

With my camera flat on the ground I spent an hour discovering and photographing insect after insect, many of which I had never seen before. I’m no expert, but I know my insect families fairly well. Yet two of these species were so alien I can’t even tell what order they’re in! If you know, please tell me!

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These muscid flies reminded me of sandpipers on a much smaller scale. Both patrol the same mudflats, probing the ground for food. The flies, however, let me watch them from inches away.
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This even smaller fly might be contributing to the sandpipers’ food supply. Occasionally I saw the fly press the tip of her abdomen to the mud, perhaps laying eggs or larvae that the sandpipers would certainly slurp up.
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Almost every one of these flies was paired with a mate. Presumably, the male is on top, guarding his female from other males while she tries to go about her life as normal. I don’t know that for sure, but I do know of another species that mates this way.
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This mystery insect delicately unfolded her cellophane wings in front of me. I have no idea what kind of insect it is. A beetle?
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Another mystery insect. I’ve never seen anything like this!
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At first I thought this little jewel was a tiger beetle, but I later learned that it’s a marsh ground beetle (Elaphrus sp.). Never seen one before!
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Springtails were the tiniest and most abundant invertebrates present, but finding them in my viewfinder was impossible because of their size. I only managed this photo because the springtail jumped into the frame while I was photographing the flies in the background.
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Above the muddy valley, a spider hunted for prey.

After completing my goal of photographing every species I could find in that puddle, I got up, stretched my very sore neck, and walked over to the other side of the sandbar. There, I found a small pool with about a dozen small fish huddled together (later identified by Chris as Plains Killifish, Fundulus zebrinus). I began crawling over to them but stopped when I heard some splashing coming from a trickle of water connecting the pool to a larger one. I went to investigate and realized that the splashing was coming from the fish as they struggled to swim through the shallow channel! Like tiny salmon, fish after fish darted through this passage. I wish I knew more about them, but I can only guess that they were on a reproductive migration.

The killifish were extremely wary and freakishly good at spotting me from underwater. I crawled up to their stream and lay still, waiting for them to swim by. I don’t know how they could see me so easily, but I learned that if I moved even the slightest bit they would panic and turn back. After many frustrating failures, I only managed to record a few mediocre videos of this fascinating behavior. To give you an idea of how quick these fish were (and how hard it was to photograph them), these videos are in slow motion at half-speed.

At this point my knees, neck, and elbows could tolerate no more strain. I walked back to my car smeared with mud and drawing lots of puzzled looks. But that was okay, because that mud had given me an afternoon of joy and wonder. If you ever find yourself bored in nature, I recommend you get off the trail and on your belly.

Hubbard Fellowship Blog: Ant Swarm (and Lunch)

This post was written by Evan Barrientos, one of our Hubbard Fellows.  Evan is a talented writer and photographer and I encourage you to check out his personal blog. If you would like to see more of his photographs, you can follow him on Facebook.

Don’t worry, I didn’t eat a swarm of ants. But late last September while I was harvesting seeds I did notice enormous clouds of small flying insects swarming above the prairie. The swarms were constantly shifting shape but they were roughly the size of small cars slowly floating across the land. Intrigued, and slightly mesmerized, I walked directly beneath one.

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Closer up I could see that the mystery insects had very narrow waists, which suggested that they might be in the order Hymenoptera (ants, bees, and wasps). Their brown color made me think they might be flying ants.

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Then I began to notice several individuals crawling in the grass below the swarm. Some were caught in spider silk; not complete webs, but loose strands of silk. Looking around, I realized that there were dozens of silk strands scattered among the grasstops of the prairie. As I knelt to photograph one ensnared ant, I saw a small jumping spider stalking another. The spider crept up, grabbed the ant, and carried him away for lunch. Were these silk strands deliberate traps set by the jumping spiders or were they just remnants of ballooning juvenile spiders that happened to catch the ants? I still don’t know.

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Later, I sent the photo below to James Trager, an ant expert, and learned that these were in fact flying ants, Myrmica americana to be specific. It still AMAZES me that there are people who can identify insect species  from just one photo!  He explained that there are actually three different species that currently are all called M. americana because two have not been officially named yet. The unnamed species I encountered is very common, which shows how much we still have to learn about even the insects in our backyards.

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Not only did Trager know the species’ name, but also the explanation for their hypnotic swarming behavior. When it’s time for M. americana to reproduce,  winged males swarm together, forming what’s called a lek.  Reproductive females are drawn to the spectacle and watch from the leaves below. Males will periodically descend from the swarm to crawl around in search of females to mate with (or get snagged by spiders). If a male is lucky enough to avoid the predators below, he may find a female to copulate with. But the challenge doesn’t end there. Once a male begins copulating, dozens of other males will often swoop in and try to do the same, forming what’s called a “mating ball.” After the whole fiesta has ended, the female pulls out her wings (so that she can convert her wing muscle into food to feed her offspring via glandular secretions) and walks away in search of a place to start her own colony.

Finally, here’s a video of the lek, first at full speed, then in half-speed slow motion.

Photo of the Week – July 9, 2015

Upright yellow coneflower (Ratibida columnifera), aka Mexican hat, is blooming all over the Platte River Prairies right now.  As with most showy flowers, the coneflowers are crawling with insects of many kinds.  I spent a fun half hour (31 minutes, to be exact) last week, trying to photograph as many of those insects as I could before I had to pop into our field headquarters for a meeting.

Bee on upright prairie coneflower.  The Nature Conservancy's Platte River Prairies, Nebraska.
Sweat bee (Halictus ligatus, I think) on upright prairie coneflower. The Nature Conservancy’s Platte River Prairies, Nebraska.
Bee and beetle on upright prairie coneflower.  The Nature Conservancy's Platte River Prairies, Nebraska.
The same sweat bee species on a different flower, this time joined by a small brown beetle.
Bee on upright prairie coneflower.  The Nature Conservancy's Platte River Prairies, Nebraska.
A different bee with the antennae of another insect beneath it.
Hover fly (Syrphid) on upright prairie coneflower.  The Nature Conservancy's Platte River Prairies, Nebraska.
It took me a while to finally capture an image of one of these syrphid flies (hover flies).  They were a lot more skittish than the bees.
Long-horned beetle on upright prairie coneflower (Ratibida columnifera).  The Nature Conservancy's Platte River Prairies, Nebraska.
Long-horned beetle feeding on pollen.

I wrote about long-horned beetles last summer after photographing them on the same flower species.  I think this one is Typocerus confluens, but I’m just guessing based on photos from last year.  You might remember from last year that adult long-horned beetles feed on flowers, but larvae are wood borers or subterranean root feeders.

Katydid nymph on upright prairie coneflower.  The Nature Conservancy's Platte River Prairies, Nebraska.
A tiny katydid nymph.
Tree cricket nymph on upright prairie coneflower.  The Nature Conservancy's Platte River Prairies, Nebraska.
A tree cricket nymph.

As is always the case in prairies (and nature in general), the closer you look, the more you see.  The number of insect species feeding on this one flower (and, in some cases, pollinating it) is a great example of the complexity of life found in prairies.  Complexity leads to resilience because there are multiple species that can play fill similar roles.  If one species has a bad year, others will fill in for it.  That redundancy helps keep all systems functioning all the time.

Hurray for complexity!

Photo of the Week – June 12, 2014

While I was in Iowa last week, I took advantage of some free time just before sunset to return to one of the restored (reconstructed) prairies we’d visited earlier in the day at the Kellerton Wildlife Management Area.  As I walked into the prairie, I could hear a few straggler (desperate?) prairie chickens booming on their lek and I flushed a pair of northern bobwhites from the fenceline.  Bobolinks, dickcissels, eastern meadowlarks and grasshopper sparrows were noisily announcing themselves across the prairie, and upland sandpipers were whistling and chattering above.  The insects were less noisy but were abundant, once I started looking closely for them.

Tall white indigo in restored prairie at the Iowa Department of Natural Resources' Kellerton Wildlife Management Area.
Tall white indigo in restored prairie at the Iowa Department of Natural Resources’ Kellerton Wildlife Management Area.

As the sun lowered itself toward the horizon, I reflected upon the various ways the success of this particular prairie restoration effort could be measured.  It was certainly aesthetically pleasing, plant diversity was high, wildlife and insects certainly seemed to be responding well to it, and by replacing cropland with prairie, the Iowa DNR had – at least incrementally – defragmented the grassland landscape.  Seems like success to me!  …I decided to focus on the aesthetics for a while, and took advantage of the golden evening light until the sun disappeared completely.

A stinkbug on purple coneflower.
A stinkbug on purple coneflower.

 

Crab spider on Ohio spiderwort.
Crab spider on Ohio spiderwort.

 

A bug (Hemiptera) sits perched in the late day sunlight.
A bug (Hemiptera) perches in the late day sunlight.

 

Ohio spiderwort.
Ohio spiderwort in the afterglow of the sunset.

 

Photo of the Week – May 30, 2014

I made another trip up to Griffith Prairie last week.  It looked pretty much as it had the week before – still lots of ragwort blooming –  but the photographs I returned with were very different.  This time, I came home with a bunch of photos of dumb invertebrates.

(I don’t mean that invertebrates as a group or concept are dumb, rather that the particular individuals I photographed seemed not to be very smart or savvy.  I’ll explain in a minute.)

Since I’d spent quite a bit of time photographing landscapes on my previous visit, I decided to put my macro lens on the camera and look for insects this time.  It was immediately clear that the long winter had dulled my insect photography skills…

First, I had to get my brain refocused on the idea of finding small creatures.  That part actually came back fairly easily.  Second, however, I had to work on my approach once I spotted those small creatures (come in low and slow).  I started by tracking some damselflies that were flitting just ahead of me as I walked.  I’d wait for one to land, then creep slowly toward it.  Unfortunately, just as I’d set my tripod down and lean forward to focus, the damselfly would fly about 2 feet further away and I’d have to repeat the whole process.  That highlighted the third aspect of insect photography I had to recapture… patience.

This was not the first damselfly I tried to photograph...just the one that finally let me get close enough to get a picture of it.
This was not the first damselfly I tried to photograph…just the one that finally let me get close enough to get a picture of it.

I did finally manage to get a photo of a damselfly.  I think it was a matter of following several different ones until I found one that wasn’t as skittery.  Of course, that’s probably a bad sign for the potential survival of that individual damselfly, since skittery is a good tactic to avoid predation.  I often wonder whether the insects I photograph are the ones that are not long for the world…

This returns us to the “dumb insect” topic.  Do you suppose smart insects look different from dumb ones?  I’ll probably never know because the only invertebrates I can photograph are the ones that are too dumb to run, jump, or fly away!

Here is a selection of some of the invertebrates that hung around on ragwort flowers long enough for me to photograph them last week.  I wish them the best, of course, but I’m not optimistic about their long-term survival…

This tiny beetle was on several ragwort plants.  Most of the beetles turned away or jumped to safety when they saw me coming, but this one didn't.
This tiny beetle species was on several ragwort plants. All of the other similar-looking beetles turned away or jumped to safety when they saw me coming, but this one didn’t.  It appeared to be enjoying its pollen dinner too much to bother running away.  It’s probably inside a bird or spider by now.

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Not a very smart little fly...
Not a very smart little fly…

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I must have seen two dozen crab spiders before I got this photo.  All the rest of them crawled beneath the petals when I approached, or dropped to the ground if I kept coming.  This one just sat there.
I must have seen two dozen crab spiders before I got this photo. All the rest of them crawled beneath the petals when I approached, or dropped to the ground if I kept coming. This one just sat there.

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I got several photos of various individuals of this bug species (a true bug - Hemiptera).  Maybe the whole species is not so smart?
I was able to photograph several individuals of this bug species (a true bug – Hemiptera). Maybe the whole species is not so smart?

It was pretty neat to see the diversity of insects and other invertebrates using this one species of wildflower.  There were quite a few more than I’m showing here because most of them didn’t stick around long enough to be photographed (the smart ones).  I’m grateful to those that did.

…and I bet there are some grateful predators out there too.

Follow up to my earlier Swallows-on-Cold-Days Post

I posted earlier this week about swallows feeding from the surface of water bodies during a cold and windy day.  In that post, I included a link to a report on a mass die off of swallows and intriguing research on some rapid evolution of swallow body and wing sizes by Mary Bomberger Brown at the University of Nebraska – Lincoln.  I intended to follow up with Mary to get more information, but she beat me to it and contacted me first!  I asked for permission to share what she told me, and she agreed.

This is what Mary had to add to my short blog post:

This sort of foraging behavior is fairly common in the swallows, especially at this time of year when the birds are transitioning from migration to nesting. All of the swallows that occur in Nebraska (Bank, Barn, Cliff, Purple Martin, Tree, and Violet-green) do it. They are picking insects off the surface of the water—insects just emerging as flighted adults from aquatic instars, surface species (e.g., water striders) or moribund adults floating on the surface. Usually swallows feed on concentrations of insects caught up in thermals, mass emergences or mating swarms. Those concentrations form in the sort of weather conditions that allow thermals to form (warm, sunny, high barometric pressure days). On cool, wet, cloudy days (low barometric pressure days) thermals don’t form, insects don’t swarm and hungry swallows are left to pick insects off the water surface. With their long wings swallows aren’t particularly well-designed for that type of acrobatic flight, so, energetically, that style of foraging is probably ‘net loss’ or ‘even sum’ for them, but better than not foraging at all. You can think of swallows as being flying barometric pressure indicators—low pressure, insects down low, so swallows down low, high pressure, insects up high, so swallows up high.

 

And, about the 1996 Cliff Swallow weather kill—Cliff Swallows (and probably most swallows) typically carry fat reserves sufficient to carry them for about 4 days without feeding, beyond that they starve and die. In the last week of May 1996, the weather was cold, wet, windy and miserable across the Great Plains. It was too cold for insects to emerge and/or fly. The swallows got wet and chilled when out trying to feed on insects that weren’t available…the only successful foraging they could do was picking insects off the water surface. The swallows survived for 4 days, but on the 5th day as much as two-thirds of the population died. The swallows that survived had shorter wing and tail feathers, larger skeletons and were perfectly bilaterally symmetrical, meaning they were efficient, acrobatic fliers that could carry larger fat reserves. The swallows that did not survive were just the opposite. In the years following the weather kill those swallows and their descendants have maintained the shorter feather lengths and larger skeletons (there was significant survival selection for those heritable traits).

 

The road kill study mentioned in the last paragraph of the blog showed that the wing feather lengths of Cliff Swallows nesting on bridges and road culverts declined significantly over the past 30 years. The shorter wing feathers made them more efficient, acrobatic fliers that could better avoid being hit by cars/trucks/SUVs/RVs and survive to reproduce, producing offspring who also had shorter wing feathers. The presence of humans on the landscape with their roads and vehicles was the cause of significant survival selection for that heritable trait…a demonstration of birds adapting to accommodate anthropogenic change in the environment. The two results (bad weather and road kill) are similar (shorter wing feathers leading to more efficient, acrobatic flight and survival selection), but with very different causes, one natural and one unnatural.

Many thanks to Mary for this great information!