And now they are eating…caterpillars!

Almost two weeks ago we solved the mystery of what warblers were eating in the streets of south Oak Park: Beetle larvae!

Well, the beetle larvae are not longer tumbling from our elm trees, but the warblers and thrushes and Indigo Buntings keep coming, along with tanagers and orioles and more! So, to find out what the birds are eating now, I grabbed a white plastic box lid, held it under some low elm branches, and started shaking:

I shook the elm branches and caught whatever fell off them with a white plastic lid.

Here’s what I found: Little green caterpillars! (I put the dime there. Money doesn’t grow on trees in our neighborhood.)

Little green caterpillars that have been feeding on newly opened elm leaves.

Just in case someone out there can identify what type of moths or butterflies these become, here are some closer views:

Little green caterpillar number 1.

Little green caterpillar number 2.

I can’t identify the caterpillars, but I do know they taste good to birds. During the past week, we’ve seen 23 kinds of warblers feeding in and under our elm trees:

Golden-winged Warbler

Tennessee Warbler

Orange-crowned Warbler

Nashville Warbler

Northern Parula

Yellow Warbler

Chestnut-sided Warbler

Magnolia Warbler

Cape May Warbler

Yellow-rumped Warbler

Black-throated Green Warbler

Blackburnian Warbler

Palm Warbler

Bay-breasted Warbler

Blackpoll Warbler

Black-and-white Warbler

American Redstart


Northern Waterthrush

Mourning Warbler

Hooded Warbler

Wilson’s Warbler

Canada Warbler

Feeding along with the warblers we’ve seen:

Yellow-throated Vireo, Warbling Vireo, and Red-eyed Vireo

Veery, Gray-cheeked Thrush, and Swainson’s Thrush

Gray Catbird

Summer Tanager and Scarlet Tanager

Rose-breasted Grosbeak

Indigo Bunting

and Baltimore Oriole

These birds are all spring migrants. The Catbird is the only one who’s likely to stay and nest in our neighborhood. The caterpillars in our elm trees have helped them survive and refuel before the next night with southerly winds to speed them on their journey north.

Did I mention that last week we found thousands of tiny caterpillar poops on our cars each morning? The polite term for caterpillar poop is frass. This morning our cars were almost frass-free, although there was lots of bird poop on our windshields.

We’ll finally get some southerly winds later this week, so we expect most migrant birds to continue north. In their wake we expect our elms to enjoy an almost caterpillar-free summer.

Now if we could just find a biological control for the bark beetles that spread Dutch Elm Disease….

Look What’s Falling from Our Elm Trees!

Every spring there are a few days in late April and early May when we see warblers in the streets, feeding on something. Two years ago it happened in late April, as seen in these photos of Yellow-rumped Warblers on our south Oak Park  block:

Yellow-rumped Warblers feeding on South Elmwood Street, April 27, 2009

Yellow-rumped Warbler on South Elmwood Street, April 27, 2009

Well, it’s been happening again the past few days. It’s like a block party for the birds, and it got me wondering–what’s for breakfast, lunch, and dinner? What tasty things are the warblers feeding on?

My best guess was that there was some sort of insect feeding on the opening leaves of the American Elms that tower over many sections of our block. Every spring there are also warblers feeding on something in the treetops, and every year there are tiny holes chewed in the leaves:

American Elm leaves - note the insect-chewed holes.

So, I was thinking that maybe whatever was feeding on the leaves somehow fell to the ground, where sharp-eyed warblers could spot them on the asphalt and continue their meals.

To test my hypothesis, I placed a white plastic lid where it could catch whatever was falling. I left it there from late afternoon yesterday until early this morning:

White plastic lid set up to catch whatever fell from the elms. May 4, 2011

Then, this morning, I brought the lid inside to see what I could find. It was covered with tiny, pale yellow grub-like insect larvae!

Tiny, pale yellow grub-like insect larvae that fell onto the lid

Closer view of grub-like insect larvae

So, one question answered: That’s what’s falling from the trees, and probably what the warblers are eating. But many questions remain:

  • What are these things? Hatchling caterpillars, or some other kind of insect?
  • Why are so many falling from the trees? Shouldn’t they be better adapted to hang onto the leaves? Or do they “jump” whenever a bird is picking at their leaf?
  • Once they hit the ground, they are still alive–you can see them moving. Can they somehow continue to live on the ground, perhaps feeding on fallen elm leaves and elm seeds? If so, when they are larger and stronger, would they climb back up into the trees?

So, I guess our next challenge is to try to raise a bunch of the larvae until they are large enough to identify. And once they are bigger we can put some of them at the base of an elm tree and see what happens.

I’ll let you know what happens!


A few hours I posted this, a Facebook friend and garden designer made this comment (Thanks, René!):

“I’m no entomologist, but after some research, my best guess is Elm Leaf Beetle. These guys feed on elms and drop to the ground in large numbers as little yellow guys to pupate. Sounds like the yellow-rumped Warblers are doing a good job of natural pest control.”

Here’s a photo of Elm Leaf Beetle damage:
Here’s a drawing of the Elm Leaf Beetle life cycle:
Here’s a photo of some Elm Leaf Beetle pupae:

We’ve put some of our fallen larvae (or whatever) into a plastic box with newly opened leaves–now we’ll see what happens!


Here are links to our earlier blog posts about birds in our streets:

First Hard Freeze for Our Jars of Water

Back on November 29th we started an experiment on our front porch, with four plastic jars filled with water. At the start of the experiment, the jars looked like this:

Water jar experiment, Day 1, November 29, 2009
Here's what the experiment looked like five days ago, before the temperature hit the freezing mark.

Now, here’s what the experiment looked like on Friday, December 4th, after the air temperature went below freezing, hitting 24 degrees Fahrenheit overnight:

Water jar experiment after a hard freeze, December 4, 2009.
Here's what the water jars looked like after a hard freeze. Three of the five jars had frozen overnight: A, B, and D. Also, we had added a fifth jar: In Jar E, the water that had been BOILED first, then cooled, put in the jar, and sealed with a lid that had NO holes in it. (Thanks to J of Science Museum of Minnesota for suggesting this addition to the experiment.)

Three of the jars had frozen water in them, including the jar with SALTY water. No one predicted that! The two jars that did not freeze were both sealed tight — there were no holes in their lids.

Here’s a closer look at Jar A, which started out as cold, fresh tap water, and was covered by a plastic lid with holes drilled in it:

Jar A (fresh water, started cold, holes in top), Decmber 4, 2009, 24 degreees F
A closer look at Jar A shows intersecting sheets of ice, more densely frozen closer to the top of the jar.

Jar B showed a similar pattern, although the sheets of ice were more horizontal than vertical:

Jar B (fresh water, started warm, holes in top), Decmber 4, 2009, 24 degreees F
Jar B also had sheets of ice, more densely frozen towards the top of the jar -- but the ice sheets were more horizontal than vertical.

Jar D was most surprising. I was expecting the salty water wouldn’t freeze, but the top part of the jar was frozen fairly solid. However, the bottom of the jar was not frozen, but had a bunch of bubbles sticking to the side of the jar:

Jar D (SALTY water, started cold, holes in top), December 4, 2009, 24 degreees F
In Jar D, notice the clear division between frozen water above and unfrozen water below.

So, that leaves us with two mysteries to solve:

  • Why did most of the water in the salty jar freeze?
  • Why did the water in the sealed jars not freeze?

I have some ideas, but I won’t tell you about them yet. However, I will give you one hint about the second mystery. Here’s what the lower part of salty Jar D looked like on December 2, 2009 — three days after the experiment started, but before the temperature dropped below freezing:

Jar D (SALTY water, started cold, holes in top), December 2, 2009, 37 degrees F
Here's what Jar D looked like three days after I had mixed in several handfuls of sidewalk salt, but before the first hard freeze. How can this help us understand why the top of the jar froze, but the bottom did not?

Feel free to tell us your ideas in the comments section (below) or on Facebook.

Last of the Fall Wildflowers at Columbus Park?

Earlier this year Neighborhood Nature showed the earliest examples of spring flowers we could find. Now that November’s two-thirds gone, I guess it’s time to show the last wildflowers still blooming in Columbus Park. (I’ll do my best to give their names, but bear with me — I’m not a botanist!)

It was sunny and almost warm during this morning’s bird monitoring in Columbus Park. However, some parts of the Park were devoid of birds, so I had time to look down as I listened hard for any birdlike sounds. These nickle-sized flowers caught my eye — I’m pretty sure they’re Daisy Fleabane. (You can see a photo of the entire plant here.)

I'm guessing Daisy Fleabane, Columbus Park, Chicago, November 20, 2009.
Although these look like daisies, the flowers are much too small. So I think it's Daisy Fleabane.

The small patch of prairie habitat beside the lagoon held two plants in flower. The first one looked like a very small example of Queen Anne’s Lace (aslo called Wild Carrot) — the flower head was less than two inches across. (You can see a photo that shows the leaves here. Please use the comments, below, to correct me if I’m wrong.)

I think this one is Queen Anne's Lace, Columbus Park, Chicago, November 20, 2009.
This one looked like a very small example of Queen Anne's Lace (also known as Wild Carrot).

I’m also uncertain what this plant is called. I’m guessing this might be False Dragonhead, a kind of mint. Another name for this species is Obedient Plant, since if you push the flowers to one side, they stay there until you push them back. However, I forgot the try that test today, so my identification has not been physically confirmed. Also, this flower looked more pinkish in the field — I’m not sure why the photos don’t do justice to the color. (You can see a photo of the entire plant here.)

I'm guessing this is False Dragonhead, Columbus Park, Chicago, Illinois, November 20, 2009.
I'm guessing this is False Dragonhead, a kind of mint. (Again, use the comments, below, to help me out!)

My final flowers were just hanging on — most of the others on this plant had gone to seed. It was a kind of thistle, found in Austin woods — but don’t ask me what kind of thistle, I wouldn’t have a clue. (Again, these looked more pinkish in the field. You can see a photo that shows some leaves here.):

Thistle flowers, Columbus Park, Chicago, Illinois, November 20, 2009.
A few thistle flowers remained, but the rest had gone to seed.

“Gone to seed” is where all these flowers are bound. Food for birds, and sometimes a feast for the eyes despite the lack of color. Check out these goldenrod seeds, which may be Showy Goldenrod, one of the most beautiful of its kind. (You can see a photo that shows more of the plant here.)

Gone-to-seed goldenrod, Columbus Park, Chicago, Illinois, November 20, 2009.
Even gone to seed, goldenrods are beautiful.

So, are these the last wildflowers I’ll see this year in Columbus Park? I’ll keep looking for more on future visits. (And I’ll also try to tame that possible Obedient Plant.)

Natural Leaf Prints on a Concrete Canvas

For the past few weeks our neighbors have been raking and blowing fallen leaves into the streets to be hauled away to someone else’s compost heap. Soon all out trees will be bare, and most our leaves will be gone — only memories of a leafy summer will remain.

Or so I thought. Until I saw this:

Natural leaf prints, Maple, Oak Park, Illinois, November 1, 2009.
Naturally made prints of maple leaves on a concrete sidewalk.

Some leaves remained as ghostly stains on the sidewalks of south Oak Park! I found the first leaf prints after a week of wet weather had given way to the first dry day. Perhaps water-soaked leaves had been plastered to the sidewalk for days, leaching biochemical stains into the sidewalk cement.

The best individual prints were along this stretch of sidewalk:

This stretch of newer sidewalk, with widely spaced young trees, had the best individual leaf prints.
This stretch of newer sidewalk, with widely spaced young trees, had the best individual leaf prints.

The sidewalk here was pretty new, smooth and fairly flat, and the trees were small and evenly spaced. When leaves were scrunched instead of flat, or when sidewalk blocks were tilted, the prints were less than perfect:

Runny leaf print, Oak Park, Illinois, November 1, 2009.
This leaf was scrunched up in the middle, so the print was incomplete. And the sidewalk here was tilted, so the stain left a streak mark as it leaked out from under the leaf and towards the street. (These imperfections provide clues to how the leaf prints formed.)

When trees above were large or closely spaced, the prints were crowded together and often overlapped:

Lots of Maple leaf prints, Oak Park, Illinois, November 1, 2009.
When too many leaves were plastered on the sidewalk, their prints overlapped and blended together.

That must be why concrete street gutters are stained brown this time of year:

Concrete gutter stained brown by water soaked leaves.
Concrete gutter stained brown by mounds of water soaked leaves.

The first prints I saw were maple leaves — I wondered if other leaves could make prints, too. Searching the neighborhood sidewalks, I found some oak leaf prints, but they were on a older stretch of sidewalk, so weren’t as well defined:

Oak leaf print, Oak Park, Illinois, November 1, 2009.
This oak leaf was printed on a stretch of older, rougher sidewalk.

Then I found some clearer oak prints on a newer sidewalk — but they were black instead of brown:

Oak prints of a different sort, Oak Park, Illinois, Nove,ber 1, 2009.
These oak leaf prints were different — they brushed away. They were made of dark, dusty dirt, not brown stain.

I looked closely and saw that these prints were made of dark dirt trapped in tiny rough spots on the sidewalk. They were dust-prints, not stains, because I could brush the prints away. I noticed that dust-prints had only formed in a sheltered spot, by a recessed door:

Site where the oak dust-prints had formed, Oak Park, Illinois, November 1, 2009.
The oak dust-prints had formed in a sheltered spot beside a little-used, recessed door.

So, here’s my guess about how these prints formed: I think a layer of dust accumulated in the sheltered spot beside this little-used door. Then oak leaves blew onto the dusty sidewalk. The previous week’s rains had first plastered the leaves to the sidewalk — protecting the dust below — and then washed away the dust between the leaves. As the weather cleared, the oak leaves dried and blew to one side, exposing the leaf-shaped patches of dusty concrete below.

Now, here’s a question: If humans provide the concrete canvas, but nature does the rest, are these leaf prints art? I think not. But an artist inspired by these prints could make art using nature’s techniques. All that’s needed for stain-prints would be  a stretch of newer sidewalk, leaves, water, and time — at least several days, I’d guess. To make the dust prints, you’d need new sidewalk, dust, leaves, and water. If I’m right about how these prints formed, you could make them in a few hours.

And if you try to do the art, you will also be testing my ideas about how the leaf prints formed. If my hypotheses prove wrong, then your art will fail, too. Hypothesis testing is science — so you’d be doing art and science at the same time!


Go here to read about the biochemistry of leaf stains. The stains may be made by tannins, or perhaps by pigments called anthocyanins.

Go here to contribute to a debate on “Is there a name for the stains left on sidewalks by fallen leaves?” Here are some of my favorite contributions from that debate (beyond “leaf stains”):

  • Ghost leaves or tannin shadows  (steef’s contributions)
  • Leaftovers  (krippledkonscious’s idea)
  • Foliagraph  (contributed by Terminal Verbosity)

If you don’t like leaf stains and want to make them go away, try here or here. (I can’t personally vouch for either site, though — you’re on your own with this issue!)


Note added Friday, November 13, 2009: On this morning’s walk I found examples of a third type of leaf print on a concrete sidewalk. Here’s a photo of imprints made when leaves fell onto a concrete sidewalk right after it had been poured — when the cement that would eventually bind it all together was still soft and wet:

Elm leaves imprinted into a concrete sidewalk, Oak Park, Illinois, November 13, 2009.
These prints were made when Elm leaves fell onto concrete when the cement was still soft and wet.

On a 20 foot stretch of sidewalk there were at least 50 prints of two types of leaves (plus a trail of squirrel footprints — more about that in another blog post). In addition to the Elm leaves, there were also a dozen prints that looked like a type of Basswood or Linden:

Elm and Basswood/Linden leaf imprints in concrete, Oak Park, Illinois, November 13, 2009.
These prints include a Basswood or Linden leaf above and two Elm leaves, below.

Although it’s hard to tell from these photos, the leaf prints were a couple of millimeters deep — that’s why I called them imprints. Because many of the prints were so perfect, I imagined that the leaves must have stayed in the concrete until after the cement had set, perhaps rotting in place. However, as shown in the photo above, some prints were not perfect — the leaves were folded or had slipped to one side after they had fallen into the soft cement.

So, I’m wondering if we can tell anything more from these imprints. Because there are so many leaf prints, does that mean the sidewalks were poured during autumn, when leaves were falling? Did strong winds blow the leaves onto the concrete and then fold or slide some once they were embedded in cement? Perhaps the evidence can’t rule our other possibilities, but it’s interesting to speculate.

By the way, other folks have posted photos of similar leaf imprints on the web.  Some folks call them “sidewalk fossils,” and teachers sometimes use them to get students thinking about how fossils form:


If you’d rather make your leaf prints in a more portable form, here are some web pages to help get you started:


Our First Ice of the Season!

According to the closest Oak Park weather station, the temperature hovered just above freezing early this morning. But skies were clear, so heat radiated from the upper layers of our backyard pools. By dawn we had our first backyard ice of the fall:

The first ice of the season formed as heat radiated from the upper layers of the water.
Ice formed as heat radiated from the surface layer of water.

If it had been cloudy, or if there had been a breeze to circulate the water in the pool, we wouldn’t have had ice. But with a clear sky and calm air, we got these fantastic ice patterns right outside our back door!

Why the triangles in the ice? I’m not sure, but that’s the pattern we got last year in similar situations. If you look at this blog post from last February, you’ll see another example of triangular-patterned ice. That post talks about “wrinkles” forming in the super thin ice — maybe triangles develop where three wrinkles intersect. Anyway, that’s a puzzle for me to work on over the next few months.

There’s no natural water where kids can go and play, except after big storms and snow melts, and they set things up so even that’s supposed to drain away. There are no streams, no lakes closer than Columbus Park — just some human-made garden ponds in fenced off yards. And the Park District swimming pool. And the drainage ditches along the highway, which have cattails and Red-winged Blackbirds and mosquitos, but those are also fenced off too. But there’s no stream or pond or swamp where I can let the boys wade free, throwing rocks, racing sticks, collecting frogs and eels.There’s no place like I had growing up.So, we import our water through pipes, then fill containers in our back yard. There’s a plastic swimming pool where our pet turtles swim in summer; another half sand, half water, with a pump to make a stream; a pool with buggy water from the golf course pond behind Grandma’s condo; a black container for panning gold; and a pool that’s just for playing.

Every fall I promise to drain the pools and store them, but it never happens. Then I wake up on a winter morning and find this

Cicadas Are Singing, So It Finally Sounds Like Summer!

Despite the cool start to the day, Annual Cicadas have been singing almost continuously since the boys left for school. It finally sounds like summer — on September 1st!

So far I’ve heard three kinds of cicada songs: A slow-pulsing buzz, a faster-pulsing buzz, and a high-pitched, continuous whine. The best matches I’ve found for these songs are Scissor-grinder, Dog-day, & Linne’s Cicadas, respectively. Recordings of these cicadas (and many other insects) are online at the Songs of Insects website, here.

By the way, I’m glad someone finally gave common names to these cicadas! I especially like the name “Scissor-grinder Cicada.” Also, the folks who did the Songs of Insects website have a book with CD. We’ve got copies, and they are both beautiful and useful.

One more thing: I’ve still only seen two adult cicadas in our neighborhood this year: One sitting on the side of our neighbor’s house and another that a Robin was trying to catch — the Robin dropped it when it saw me coming. I wonder if adult cicada numbers will increase through September, or if the cicada nymphs still in the ground will just wait until next year.

Caterpillar in the Street: Tragedy or Transition?

During a break in this afternoon’s rains, I was walking along our street checking for migrant birds. Something caught the corner of my eye — I looked down and found this:

I found this sphinx moth caterpillar laying motionless on the street, under an American Elm tree.
I found this three-inch sphinx moth caterpillar laying motionless on the street, under an American Elm tree. The head is on the left, the hind end (with its horn-like projection) on the right.

We find at least one of these caterpillars each summer, always on the street or sidewalk under an American Elm tree. The green color, overall shape, and especially the pointed projection on the tail convinced me that this must be some kind of hornworm — the caterpillar stage of a sphinx moth.

The caterpillar was motionless. I wondered if it had fallen 30 or 40 feet from the tree above and died. Just in case it was merely stunned, I brought it in our house and put it in a plastic box with some elm leaves. When Ethan and I checked it a few hours later, it was moving its head slowly, stiffly swinging back and forth, so it was still alive. Maybe we could save it!

Then we had a brainstorm. We knew that many hornworms dig into the ground and make a pupa — the transition stage from caterpillar to moth — without spinning a cocoon. And caterpillars often stiffen up before they split their skins, revealing the pupal stage within. Maybe this caterpillar had dropped to the ground on purpose, but had the bad luck to land on the street rather than soft soil. So we added some damp sand to the box, set the caterpillar on the sand, and waited.

Two hours later Ethan checked the box — the caterpillar had disappeared! However, a bit of digging revealed that it had merely dug its way into the sand and curled up into a tight C-shape. We left it alone, because pupating caterpillars can get all messed up if you bother them during this critical transition.

We’ll check again tomorrow and let you know what happened.


Update: The caterpillar continued burrowing in the sand, digging all around the container and finally settling into a rounded cavity just below the surface. Then, after about a week, it died without making a pupa. It turned out to be a tragedy after all. We were very sad.


Follow these links for more information about sphinx moths:

If our caterpillar pupates successfully we’ll have a sphinx moth to identify, which may be easier than identifying a caterpillar or pupa.

What Happened to this Year’s Cicadas?

I’m still wondering what happened to this year’s cicadas in our neighborhood. It’s a warm day in late August, yet it’s way too quiet here in south Oak Park. With all our big old trees to feed cicada nymphs, we usually have a pretty deafening chorus this time of day. However, this summer the cicada chorus has been pretty much of a bust through the hot part of the day, then a little louder at dusk. My family has found about a dozen shed cicada skins, but so far no live cicadas or dead adults have crossed our paths. What’s more, traffic on our Kids’ Cicada Hunt home page is way down — less than half of previous years.

On the other hand, I’ve seen maybe 10 times as many Cicada Killer Wasps as usual, mostly because I saw a couple of leks* at sand traps on the Columbus Park Golf Course. Also, traffic is high on my Cicada Killer web pages (here and here, and especially this photo of my then-five-year-old son’s hand). (The week-old blog post is already number 2 with a bullet on my list of all-time top posts.) It makes me wonder what all those mommy wasps are going to feed their babies!

So, how are the cicadas in you life doing? Same as usual, fewer — or are they blasting your ears out? Inquiring minds, like mine, want to know. Is anyone else worried what happened to their cicadas?


*A Cicada Killer Wasp lek is an area where the Cicada Killers emerge and congregate, and the males fight for the right to mate with females of their species. (See here and here.)

Cicada Killer Wasps Are Back!

On this morning’s walk through south Oak Park, I got my first close look at a Cicada Killer Wasp for 2009:

This Cicada Killer Wasp kept perching on a plant overlooking a rather barren garden. That made me suspect it might be a male, guarding a space where he hoped females might dig their burrows.
This Cicada Killer Wasp kept perching on a plant overlooking a rather barren garden. That made me suspect it might be a male, guarding a space where he hoped females might dig their burrows. (The wasp must have been about an inch-and-a-half long, but it looked much larger in person!)

Most of the Cicada Killer Wasps I’ve seen have been near burrows in bare soil, like in a construction site or at the edge of a playground sandpit. In fact, just yesterday I was scanning the Columbus Park golf course, looking for birds, when I spotted a Cicada Killer Wasp at the edge of a sand trap. Then I saw another — and another — and another — until I counted 25 Cicada Killers flying just above that sand trap. Then I looked at the next sand trap west and saw at least 25 more. (Now there’s a hazard that might scare even Tiger Woods!)

This wasp was behaving differently. It kept perching on the top of an 18-inch-tall plant, flying off when I tried to take its photo, then landing again as I pulled back. Once it hovered right in front of my face, looking me in the eye, before returning to its perch. This made me wonder — was this a male Cicada Killer guarding some sort of territory? If so, I’d never seen one of those before — but how could I tell for sure? I decided to check my photos for a stinger — I expected a female would have one, but a male would not. This is what I found:

The tip of the Cicada Killer Wasp had what looked like a small stinger -- not as big as I expected.
The tip of the Cicada Killer Wasp's butt had what looked like a small stinger -- not as big as I expected.

I’ve seen really long stingers on dead Cicada Killers, but this one looked really short. What was going on?

I searched the web for answers and found some useful photos and a surprising fact (here). Female Cicada Killers can retract their long stingers inside their bodies, so you don’t always see stingers on live female wasps. However, male Cicada Killers have a pseudostinger — a fake stinger, one that doesn’t work — that you can see when they are alive.

So, it seems I really did see a male Cicada Killer in that south Oak Park garden. Next time I walk past there, I’ll look for females and burrows.


Here are some websites about Cicada Killer Wasps:

Five-year-old Ethan holding dead Cicada Killer Wasps
Five-year-old Ethan holding dead Cicada Killer Wasps