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:

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

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

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

Ovenbird

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….

Hornet Nests Now Visible in Our Neighborhood

Now that most trees have lost their leaves, we find out what was hiding in their branches all summer long. Bird and squirrel nests are suddenly visible, and hornet nests turn out to be much more common than we ever imagined. I almost never see a Bald-faced Hornet in summer, but now I’m finding their nests in many trees in Columbus Park and throughout our Oak Park neighborhood. They look like big gray basketballs silhouetted against the sky:

Hornet nests look like big gray basketballs or balloons stuck in trees.

But when you get closer, you can see the arcs of hornet-made paper, glued by hornet “spit” to build the outer layers of the nest:

Hornets chew up dead wood, mixing it with saliva to make their own brand of paper.

Some brave creature tore off the bottom of this nest:

I'm hoping whoever tore into this nest waited until all the hornets were gone. (Worker hornets die off each fall, and next year's queen hornets burrow into soil or rotten logs to spend the winter in suspended animation.)

The outer layers of protective paper were torn away, exposing the inner cells — hexagonal tubes that look a bit like honeycomb:

Although the inside of a hornet nest looks like the honeycomb inside a bee hive, hornets build their entire nest with home-made paper (not beeswax).

Now, I’m not going to get all didactic and lecture you about the differences between honeybees and hornets. Let’s just say they both sting if you get too close, you’re not going to get much honey from a hornet, and honeybees won’t help control the fly population around your home. If you want to learn more, check out these online references:

• Who Are You calling a Bee, Mister?! Identifying Bees, Wasps, Hornets and Their Nests
• Wikipedia on Bald-faced Hornets
• Iowa State University on Baldfaced Hornets (I guess there’s more than one way to spell it.)
• Ohio State University Honey Bee Laboratory on Paper Wasps and Hornets
• Wikipedia on a bunch of other wasps that are also called hornets

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One of my Facebook friends had some advice for anyone who might consider bring a hornet nest inside for the winter. Patrick wrote, “I remember, as a kid, bringing one inside before the cold had done its deed to the hornets.” In other words, wait until there have been a couple of good hard freezes to kill off any remaining hornets (or other insects) inside the nest.

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P.S. Thanks to the Columbus Park walker who told me where to find the broken-open nest!

Caterpillar Found Under Dead Leaves

This afternoon Ethan was raking leaves when he found a beautiful, silky brown caterpillar on the curb, under dead elm leaves:

Ethan found this caterpillar, a bit more than an inch long. Can you tell which is the head end? (If you guessed the left end, then the caterpillar escaped with head intact, you silly bird!)

This caterpillar probably fed on leaves this summer and early fall. Now it’s looking for a safe place to shed its skin and enter a resting stage, while it changes into a moth. (The resting stage is called a pupa, which may or may not live in a cocoon.)

But, what kind of caterpillar is it? What kind of moth does it become? My old moth and butterfly field guides did not illustrate a match, but we did find a somewhat similar caterpillar pictured online. So, maybe it’s the caterpillar of the Sloping Sallow moth — or maybe it’s not.

We released the caterpillar in our rock garden, which has lots of good places to hide and make a pupa.

If you can help us identify this caterpillar, please leave a comment, below.

Katydids 1, Cicadas 0

When I stepped outside this evening — about a half hour after sunset — I heard a single Katydid singing slowly in a backyard tree. That reminded me: Even though yesterday was 70s and sunny, and this morning was sunny and 60s, I had not heard an Annual Cicada singing either day. In fact, the last time I heard a Cicada song in our neighborhood was October 9th. Temperatures dropped below freezing in Oak Park during Columbus Day weekend, and that must have been enough to kill off the last of our Cicadas. Grasshoppers, Crickets, and at least a few Katydids are still holding on, but the Cicadas’ season seems to be over.

I like fall — I even like winter — but I’m still going to miss the Cicadas.

To hear a Katydid song, go here. To hear the song of a Scissor-grinder Cicada — the last kind heard singing in our neighborhood — go here.

We Found Tiny Insects Inside Hackberry Nipple Galls

Way back on June 18 we did a Neighborhood Nature blog post about Hackberry Nipple Galls, which you can read here. On this morning’s walk I found two Hackberry trees with half a dozen or more Yellow-rumped Warblers in them, hunting for bugs to eat. That got me thinking that maybe some of the bugs they were eating had grown up inside Nipple Galls. The warblers wouldn’t let me get close enough to see what they were eating, so instead I found some Hackberry leaves with lots of galls on them and took them home to dissect.

Before I picked them, the leaves looked like this — covered with nipple-shaped growths, called galls, that grew when insects called Psyllids (SILL-lids) laid their eggs on the leaves:

These Hackberry leaves are covered with Nipple Galls. The galls formed when insects, called Psyllids, laid their eggs on the leaves. The gall became a nursery for the baby Psyllids, which fed on the insides of the gall. The gall provided shelter and food at the same time.

After I cut open one of the galls on our kitchen table, it looked like this:

The cut-open nipple gall had a tiny Psyllid insect inside a hollowed-out cavity.

I cut open a few more galls, and more tiny Psyllids crawled out. They were about as big as the head of a straight pin:

The pinhead-sized Psyllid on the lower left was walking around, but the Psyllid on the upper right was upside down. You can tell these Psyllids are not yet fully grown, because they don't have wings. They just have "wing buds" behind the head, which will become wings after they shed their skins another time or two.

So, maybe the warblers were eating adult Psyllids that had emerged from galls on the Hackberry trees, or maybe they were eating something else. But what I really want to know is if any birds peck open Nipple Galls to catch the not-yet-fully grown Psyllids. (I’ve seen Downy Woodpeckers break into Goldenrod Galls, but those galls are somewhat larger.) I guess I’ll have to keep a close eye on any birds I see in Hackberry trees this fall. I’ll also search through Hackberry leaves for galls dissected by bird beaks instead of knives.

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Update added two days later (October 22, 2009):  Rather than throw the gall-covered Hackberry leaves outside, we put them in a container with a lid and waited to see if adult Psyllids would emerge. When we opened the container this morning, this is what we found:

There were at least four of these winged adult Psyllids in the container with the gall-covered Hackberry leaves. (Because of the wings, they were twice as long as a pinhead is wide.)

Now, doesn’t that look like a good snack for a warbler?

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You can read more about Psyllids and Nipple Galls here and here and here.

Cicada on the Sidewalk: Not Quite Dead

Adult cicadas face a rough transition from nymph to adult and are always in danger of being eaten. However, quite a few cicadas do survive to mate and lay eggs. By late summer these survivors start to die of — what else can we call it? — old age.

So, a few days ago Aaron found our first half-dead Annual Cicada of the year. It just lay there on the sidewalk, legs folded up, as if it was asleep:

The dying Annual Cicada just lay there with its legs folded under its body.

When I picked it up, it started to buzz, vibrating my finger tips. But stopped after two seconds. Turning it over, we could see some body parts involved in making the buzzing sound (red arrow), plus the long, pointed beak it sometimes uses to suck sap from plants (blue arrow):

Underside of the Annual Cicada. The red arrow points to a protective covering (operculum) for the sound-producing organs. The blue arrow points to the tube (beak) that cicadas use to suck plant juice and occasionally jab a threatening animal -- or human.

Aaron and I decided to leave the dying cicada in peace. It was gone the next day, so it may have been found by a hungry bird or curious human.

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As noted in the caption, the part you see under the body is only protective — it doesn’t make the sound. The part that actually vibrates to make the buzz is up under the wings, and the muscles that cause it to vibrate are inside the body. If you’re interested in knowing more, there’s a detailed, illustrated description of cicada anatomy here. There’s a good technical description of how cicadas make sound here.

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Here’s an interesting observation about humans and cicadas. Although most years Annual Cicadas start singing in late June or early July, I’ve noticed that my Kids’ Cicada Hunt website doesn’t experience a big jump in visitation until 4 to 6 weeks later — when the cicadas start to die. I guess hearing cicadas doesn’t inspire much interest, but a cicada in the hand is worth a visit to cicada website or two. (My site is usually on the second or third page of results.) For comparison, my website statistics can tell when the first Cicada Killer Wasps emerge within a few days. The sight of a giant wasp inspires lots of folks to head for their computers, where they often find this picture of five-year-old Ethan holding dead Cicada Killers.

For a more complete analysis of when people visit my cicada website, check out this old CicadaBlog post.

Cicada FAIL: Growing Up Is Hard To Do

Maybe that title is a little harsh. Cicadas go through a lot as they convert from underground nymphs to adults flying through the treetops. Lots has to go right for it to happen, involving hormones and other complex biochemical activities on the inside and major changes to their bodies on the outside. And a lot of things can go wrong.

I’m not sure what happened here, but something cut short the life of this Annual Cicada, preserving it forever frozen in a transition from nymph to adult:

This nymph crawled out of the ground, climbed a wall, locked itself in place, and started to shed its skin -- but died before it could complete the transition to adult. The dead adult dried, darkened, and mummified into its current form.

I even feel a little guilty for displaying its dead body this way. Maybe we’ll go back and retrive it from the wall, and bury in our backyard pet cemetery. Or maybe we’ll let the ants do their job.

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To see what would have happened if everything had gone right, check out this series of photos on our Kids’ Cicada Hunt website.

This blog post discusses deformities and other things that can go wrong as cicadas transform from nymphs to adults.

Cardinal Eats Cicada: Two Interests Collide

Usually it’s kind of nice when two of our family’s interests intersect. But I’m still trying to decide how I feel about what happened this morning when a Cardinal caught and ate an Annual Cicada in our neighbor’s elm tree:

The Cardinal ate the cicada bit by bit. In this photo it's holding the cicada's wing and part of its body.

One problem we have when birds and bugs interact: Who do we root for? We love cicadas, and we love birds, and one gets eaten by the other! Usually we’re OK with birds eating cicadas, since adult cicadas die off in the fall anyway. But this year there aren’t as many cicadas around, so today’s encounter left me a little sad.

The Cardinal looks a little ratty in this photo, and it’s not just because the photo’s fuzzy. The Cardinals in our neighborhood are molting — shedding their old summer feathers and growing a new set for the winter. That’s why most Cardinals we see right now look bald. They’ve molted their old crests and the new ones are just getting started. Adult female and young Cardinals have similar greenish brown feathers, but I think the Cardinal in this photo is a female, because it has a bright red-orange bill and reddish on the wings.

Two other things about our neighborhood’s Cardinals right now: The males stopped singing a few days ago — they must be done defending the breeding territories they used this summer. Also, there are lots of young-of-the-year Cardinals around right now — sometimes the young ones chase the adults around our yard begging for food. I guess her babies were somewhere else, though, because this mommy Cardinal got to eat her cicada in peace.

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Note added Tuesday, September 8, at 8:30 a.m.: I just saw a House Sparrow carrying off a cicada! Counting its wings, the cicada was half the length of the sparrow’s body. The sparrow hid in some brush, perhaps hoping its flockmates would not notice its catch.

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For more information about Northern Cardinals, visit All About Birds. For more information about Annual Cicadas, try our Kids’ Cicada Hunt website.

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 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.

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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.

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Follow these links for more information about sphinx moths:

• Hornworms and “Hummingbird” Moths from Colorado State University Extension
• Elm Sphinx (Ceratomia amyntor). This web page shows the Elm Sphinx as having four horns — the one we found only has one. So, even though it seems to eat elm leaves, it must be a different species.
• Twin-spotted Sphinx (Smerinthus jamaicensis). The caterpillar shown on this page is a better match for ours, although not a perfect one. However, the text says the “larvae can show considerable variation.” According to the Colorado State University Extension site, some Twin-spotted Sphinx caterpillars eat elm leaves.

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