First Flags Over Brookfield

by Carl Strang

Cicada specialist John Cooley taught me a new term: flagging. This refers to dead and broken twig ends on trees and shrubs where periodical cicadas have placed their eggs. Mama cicada slits the underside of the twig in several places and injects her eggs. This impedes water flow, and with circulation cut off the leaves turn brown. The cuts weaken the twig, and it may break partly and bend down, producing a “flag.”

Now that the periodical cicadas are done singing in many places and nearly so in others, it is time to start looking for these flags. They will provide the best measure of how this off-year emergence may continue for another generation. On Tuesday I started in Brookfield, the first place where I heard a full wave chorus of singing males.

I soon found a tree with many flags.

This tree was in the same place where I found that initial wave chorus.

The brown, drooping flags stand out against the green foliage. This prunes the tree a bit but will not cause significant harm. I saw many trees with one or two flags, but only the two in the photos had many. I expect to see more of them the next time I check.

John said that dry weather and thunderstorms enhance flag formation. A lack of water flow enhances the twig-end drying, and the buffeting winds of storms partially snap the weakened twigs. I heard no singing cicadas in Brookfield, and so this is the very beginning of this process. On the way home I swung through northern Hinsdale, another area that had abundant wave chorusing at the peak. There still were many small non-wave choruses, so it was not surprising that I saw only a couple flags during the drive-through. I am hopeful that flagging will develop over a period of weeks, allowing me the time needed to get a good assessment of periodical cicada reproductive success across the Chicago area this year.

A Little Celebration

by Carl Strang

It has been 30 years since I last published a scientific paper. My early papers were on birds and turtles, as my formal training focused on vertebrate ecology. As is clear in this blog, I have again become interested in scientific research, but now the focus is on invertebrates, specifically singing insects. The first scientific paper to result from this work just came out in The Great Lakes Entomologist. Here is the abstract:


Geography and History of Periodical Cicadas (Hemiptera: Cicadidae) in DuPage County, Illinois

Carl A. Strang1


The spatial distribution of periodical cicada (Magicicada septendecim L. and M. cassini Fisher) emergence in 2007 did not match either historical locations of woodlands or the cicadas’ own geography in the 19th and early 20th centuries in DuPage County, Illinois. Cicadas were present in forest areas that had remained above 61 ha throughout historic times, and they were absent from areas which at some point had been reduced below 52 ha by tree removal, mainly for agriculture. Isolation of forest areas also may have contributed to local extinctions. The insects have spread into new, urban woodlands created by residential plantings. Their distribution is associated with the early growth of towns along commuter railways in the eastern part of the county (toward Chicago). A peculiar gap in the main emergence area (encompassing two adjacent cities) may be the result of the cicadas shifting their emergence four years early. An active dispersal on 9–11 June, coinciding with the peak in cicada singing in forested areas, apparently placed scattered small groups of cicadas outside the main emergence area.

1Forest Preserve District of DuPage County, P.O. Box 5000, Wheaton, IL 60189-5000.

Two species of periodical cicadas were the subject of the paper. The larger Magicicada septendecim (Linnaeus’ 17-year cicada) is on the left, M. cassini (Cassin’s 17-year cicada) on the right.

Two species of periodical cicadas were the subject of the paper. The larger Magicicada septendecim (Linnaeus’ 17-year cicada) is on the left, M. cassini (Cassin’s 17-year cicada) on the right.

Most of the content of the paper I have posted in this blog in less formal terms, for instance:

The study isn’t done, but a few years need to pass before I can seek more information to add to the story.

Cicada Update

by Carl Strang

Periodical cicadas in small, scattered numbers have continued to appear in a large part of DuPage County. Steve Bailey, who conducts bird surveys for the state, also has heard them in parts of Grundy and southern Cook County. So far nearly all have been singing the cassini song type, except for one septendecim-like singer reported from Fullersburg Woods Forest Preserve by Naturalist Leslie Bertram.

There are so few that prospects for reproductive success are dim.

This is the expected fate for nearly all of these vulnerable individuals, to be eaten by birds, their wings plucked off and dropped to the ground.

I witnessed such a predation event myself at Mayslake Forest Preserve. A cicada got in maybe four songs before a robin flew straight to it. The insect got out an alarm squawk, then all was still.

In an earlier post I speculated about what was going on with these cicadas, which had been quiet the previous two years. A suggestion by WBEZ radio news director and nature enthusiast Brian O’Keefe reminded me of similar ideas expressed in the scientific literature when cicadas appear outside their brood’s normal area: perhaps these were transported from the southern brood XIX range in the root balls of nursery stock. That certainly could account for the ones in residential areas and in portions of forest preserves adjacent to private lands. I checked with the Forest Preserve District of DuPage County’s nursery staff, however, and none of our tree plantings in the past 13 years have come from so far south. Some of these cicadas are half a mile or more from the nearest preserve boundary. A little mystery therefore remains, but I have concluded that my time would be better spent in other directions.

Incidentally, while documenting these scattered emergences I was listening for green-winged cicadas (Diceroprocta vitripennis), another spring species which I believe emerged in small numbers in 2007. Their buzzings were largely covered by those of periodical cicadas, however, and the only hard evidence was a single wing, like the one in the photo above, but with green rather than red veins. Some of the literature suggests a 4-year periodicity for Diceroprocta, but I have encountered none in the places I thought I was hearing them in 2007.

A New Periodical Cicada Puzzle

by Carl Strang

I have been getting questions from people asking about periodical cicadas this year. They have been hearing reports of brood XIX, the simultaneous emergence of several species of 13-year cicadas to the south of our area. I have been giving the sensible answer that no, we won’t be getting them in northeast Illinois. That was up until Tuesday afternoon, when I heard three periodical cicadas singing on the Mayslake Forest Preserve mansion grounds.

The songs were those of Cassin’s periodical cicada. This is a photo from the 2007 main emergence in our area. The insect on the right is a Cassin’s 17-year cicada, the one on the left is our other local species, Linnaeus’ 17-year cicada.

But that wasn’t all. That same day I heard another singing cicada half a county away from Mayslake, at forest preserve district headquarters. Then yesterday I heard individuals at two more locations on the Mayslake preserve, and two in west central DuPage County, where there were very few scattered individuals in 2007. Furthermore, I have heard reliable reports of singing periodical cicadas in other DuPage County locations.

I don’t see any way to connect this to the 2007 emergence. True, a few late cicadas came out in 2008 (I called them Oops Cicadas), but that is to be expected. There were none in 2009 or 2010. The question I would like to have answered first is whether these are 13-year or 17-year cicadas. There is a 13-year species with the same song as cassini. I hope I can get specimens, a shed nymphal exoskeleton at least. That could be held for potential future DNA checking. This would establish whether these might be outliers of brood XIX. The thing is, most people don’t listen for singing insects. We don’t really know what is going on with periodical cicadas outside of peak emergence years or core emergence areas. If I learn anything new, I’ll pass it on, but I will try to get as many location observations as I can in the limited time I have to devote to this unexpected development.

Northern Cardinal Dossier

by Carl Strang

This time I share my dossier for a common and beloved species. As usual, it begins with the general account I wrote when I established the file in the 1980’s, then additional entries begin with my date codes.

Cardinal, Northern

The cardinal is the first bird I studied with any intensity, as a child mapping song perches of males in my neighborhood and connecting them into “territories.” Generally they selected highly exposed perches in treetops and on television antennas. The song is highly variable, but tonal qualities of voice and type of song pattern are distinctive. The alarm note is a sharp “teek,” again of a distinctive tonal quality and pitch. The female also sings, the songs following the same pattern as the male’s but sometimes lower in volume.

They nest usually in thick bushes within 10 feet of the ground. A nest at Boiling Springs, PA, was in a rain gutter closely overarched by spruce branches. Young birds in a brood observed in Lombard, IL, were kept together and off the ground by the parents.

Both sexes have bright red beaks surrounded by black feathers. When viewed head-on this has an imposing effect, the bird’s weapon thus being highlighted. No doubt this is of significance in agonistic display. Field guides, with their emphasis on lateral views, lead us away from this kind of discovery.

Cardinals feed in bushes, in trees, and on the ground. They are not acrobatic foragers. They consume large seeds at feeders in winter. Cardinals appear to show some territoriality through winter.

Songs vary among locations, individuals, and times. Each male has more than one song. Some rendered songs are: “chibone, chibone, chibone, chibone;” “What-cheer, wheet wheet wheet wheet;” they beging singing in late January (as early as 23JA83 in DuPage); “pul’see pul’see …” (~7 reps).

17JL84. Male foraging in black cherry tree spent 5-8 sec. on a perch, moving head to look at nearby leaves and twigs in small turning movements, moving 0.5-1m between perches (Willowbrook Back 40).

NO84 they were often feeding on ground, scratching in leaves.

12FE87. Heard first song of year.

5MY87. Nest with 3 eggs, of twigs (slightly loose structure) beside trail in riparian strip at Willowbrook. In honeysuckle, 5 feet up, in fork of branches. Deep cup. Eggs bluish with brown mottling. By a few days later only one egg left, nest apparently abandoned (too close to trail?).

5JE88. In the middle of Geneva I stood under a tree in which a pair of Cardinals suddenly began to alarm-call rapidly. They were close to me, but not paying attention to me. The calls were directed at a blue jay which the cardinals chased from the isolated streetside tree to a clump of trees and brush, and continued the alarm calling and chasing until the jay left. The jay resisted some, was not driven off easily.

19JA89. First Cardinal song, on Willowbrook early morn. In an unusually warm January.

9MR89. Cardinals all singing today through midday (first warm day, 40 degrees F, after a long cold spell). There seem to be too many Cardinals singing, and I see 3 males chasing each other. In this year with such a mild January and no super-severe weather, unusually high survival?

17AP89. A cool, cloudy day. Cardinals all over the Back 40 are giving constant series of “alarm” (?) notes.

29JA90. First cardinal song of year, Willowbrook.

1990. The year of the 17-year cicadas, I caught some at Fullersburg and released them at Willowbrook. One of these flew across a small forest clearing, and a cardinal flew out and caught it with its beak, in mid-air.

26JA99. First cardinal song of year, Willowbrook.

4MR99. Many cardinals singing at Willowbrook, including a female near the Nature Trail head.

3MY99. Cardinals fighting in area of white cedars at Willowbrook.

13MY99. Cardinal nest at Willowbrook in honeysuckle shrub overhanging creek. May still be under construction, though birds agitated when someone is nearby. Female incubating 17MY, 27MY.

10AU99. Cardinal songs distinctly reduced in number, length. Only a few weak, partial songs this morning.

25AU99. Last cardinal song of year noted at Willowbrook.

26AU99. Cardinal fledgling, with rapid notes, similar in pitch to adult’s note but not as sharp, and rapidly repeated rather than separate.

1NO99. Cardinal eating buckthorn berries. 

14JA00. Cardinal sang a half song in afternoon, Willowbrook.

2FE00. First full cardinal song of year, Willowbrook.

21FE00. McKee Marsh, north Blackwell Forest Preserve. A male cardinal singing from a very exposed perch at the top of a 25-foot-tall cottonwood. Doesn’t change posture much when singing. Thrusts face forward a little, but keeps bill level. Sang back and forth with other audible cardinals, answering with full songs, “What-cheer, wheet wheet wheet wheet.” The others stopped singing, it paused for some seconds, then gave a “what-cheer,” paused, did so again, and gradually added “wheet” syllables until it was singing full songs again, even in the others’ absence. When not singing, turned head to look all around.

25FE00. Willowbrook. Several juncos and cardinals singing this morning. A display by a male cardinal that was singing at the service road junction with the Nature Trail. A female was in the same tree, and for a minute or two the male faced her, occasionally adopted an extended, stretched out body posture unlike the normal singing pose, moved with body held rigidly, and emitted a chattering dry trill between some of the songs, all the while facing the female. She stayed in place, he never approached within less than 5 feet, and he then turned away from her and resumed singing normally.

1JL00. A female yellow warbler feeding a cowbird fledgling near the south end of Silver Lake, Blackwell. Earlier this week a pair of scarlet tanagers were feeding a cowbird at Willowbrook, and half a dozen times this spring I have seen male cardinals feeding them (some were the same pair, but at least 3 different broods involved) also at Willowbrook.

2SE05. Had to re-learn fledgling call of rapid high notes lacking sharpness of adult alarm. May have been contact call rather than alarm, though adult nearby gave very occasional alarm, too.

7JA08. Fullersburg. A cardinal sang, briefly and uncertainly, but definitely. My earliest noted song (previous earliest 14JA00). Temperatures in the 50’sF past couple days.

15JA10. Culver. First cardinal song of the year.

5OC10. Mayslake. Singing: white-crowned sparrow, phoebe, cardinal, song sparrow.

7DE10. Mayslake. A cardinal singing, full strong song repeated a couple times. Sunny day but cold, teens F. (I have heard cardinals singing on occasion all through the middle of this winter, the first time I have observed such an extended singing period).

Another observation in recent years is that cardinals in our area seem to raise mainly cowbirds early in the season, but a final August nest nearly always produces only cardinals. If this is correct, it implies a strong selective pressure, at least locally, for shifting the nesting season later.

Literature Review: Cicadas and Trees

by Carl Strang

The phenomenon of the periodical cicadas raises a lot of questions. Some of these questions are ecological. Millions of the insects emerge at once every 13 or 17 years, depending on the area, and their sheer biomass suggests that they must influence the ecology of the forest as a whole. Their nymphs grow by drawing sap from tree roots. The adults damage twigs when they cut them to insert their eggs. When the masses of cicadas die, their decomposition releases nutrients into the soil. Thus, from a tree’s standpoint some of the effects are potentially beneficial, others harmful. This was the background for the paper I am reviewing today (Speer, James H., Keith Clay, Graham Bishop and Michelle Creech. 2010. The effect of periodical cicadas on growth of five tree species in Midwestern deciduous forests. American Midland Naturalist 164:173-186).

Periodical cicadas also occasionally feed on tree sap during their brief time in the adult stage. These are sitting very still, and their beaks are piercing the bark.

This research group used dendrochronology methods in southern Indiana, measuring growth ring widths in several tree species. They first factored out climatic influences, ruling out the effects of relatively good or bad growing seasons. Then they tested the effect of feeding by cicada nymphs, oviposition damage and the nutrient pulse following emergence.

Periodical cicada nymph emerging from the ground. Did the nymphs’ diet of tree sap impact tree growth?

Cicada nymphs start out very small, and grow to be relatively large, so if their numbers are impacting tree growth, the trees should grow progressively slowly through the insects’ 17-year cycle. Speer and associates could find no nymphal feeding effect in any of the 5 tree species they examined.

Periodical cicada egg slits in a redbud twig. Typically the twig end dies as a result of this damage.

Sassafras, pin oak and black oak showed some growth loss from oviposition (egg-laying) damage, but these plants are less preferred for oviposition than sugar maple and white ash. The latter appeared to be hit harder, but growth rings showed no effect.

Dead cicadas litter the ground as an emergence ends. Does the pulse of nutrients from their decomposition benefit the trees?

There was a nutrient pulse effect for black oak, pin oak and sugar maple, but it happened 5 years after emergence. The authors suggest that trees may need time to absorb the nutrients and produce extra wood after the adult cicada mortality event. Alternatively, this effect may result from a pulse of mortality in cicada nymphs of that age.

Mast Year

by Carl Strang

Mast is a collective term referring to nuts and acorns. Trees do not produce these in the same amounts each year. In some years very few nuts or acorns develop in a given species, and in other years prodigious numbers appear. High production seasons are called mast years. 2009 is proving to be a mast year for bur oaks and white oaks at Mayslake Forest Preserve, where the trails in places are littered with the fallen acorns. Here is an example for bur oak.

Bur oak mast b

Here, white oak acorns abound.

White oak mast b

Though elsewhere I am seeing lots of walnuts, this does not seem true for that species at Mayslake, which also is having an unremarkable year for hickory nuts. Nearby, at Fullersburg Woods Forest Preserve, I noted in 2007 that walnuts, hickories and red oaks had a mast year. It is common for members of the white oak group and red oak group of species to be decoupled from one another in their mast years.

Fox squirrel 1b

As you might imagine, animals such as tree squirrels are impacted by mast years. Mayslake’s gray and fox squirrels will have an easy winter with so much food available. They help their cause by biting acorns before burying them in an effort to kill them. The acorns, in a countermeasure, are quick to sprout when they fall to the ground. A study published in 2006 in Science (314:1928) found that red squirrels (which live north and south of us, but not in DuPage County) themselves reproduce more heavily in mast years (perhaps responding to an increase in flowering or other advance cue). Such adaptive interactions between species are referred to as coevolution. The phenomenon of the mast year itself likely is, at least in part, an evolutionary tactic by the trees. By coordinating their mast production they can limit their seed-predators’ survival in some years, overwhelm them in others. Such an episodic mass reproduction is reminiscent of the periodical cicadas.

Summer Woodland Wildflowers

by Carl Strang

In summer the main wildflower action shifts to prairies and other open areas, but in recent weeks there have been plenty of species blooming in the savanna woodlands at Mayslake Forest Preserve. Tall agrimony plants have been flowering for a while, now.

Tall agrimony 1b

These small yellow flowers will produce burs to be dispersed by mammals that brush past and catch the burs’ hooks on their fur or clothing. Another species that disperses in the same way is enchanter’s nightshade.

Circaea 1b

Named for Circe of Greek mythology, Circaea is an annual that I also could have included in a weeds update because of its “weedy” life history strategy. I expect to be pulling many of its tiny burs off my shoelaces later in the season.

The flowers of Canada black snakeroot are so tiny that they are easy to miss.

Canada black snakeroot b

Also small are the flowers of white vervain, but they at least are in strings at the tops of relatively tall plants.

White vervain b

Speaking of tall, here is a more conspicuous bloomer common in a wide range of our woodlands.

Tall bellflower

Tall bellflower was the subject of a study published last year that interested me (Yang, Louie H. 2008. Pulses of dead periodical cicadas increase herbivory of American bellflowers. Ecology 89:1497-1502). Yang experimentally fertilized plants of this species with the bodies of periodical cicadas, and found that deer preferentially fed on treated plants. This was a new demonstration of how the cicadas’ abundant emergences  have a profound ecological impact.

The shorter blue-flowering plants of self heal occur in woodlands and in the open.

Self heal b

Incidentally, lowering my sights one day as I walked the slope between the friary and May’s Lake, I saw the following plant.

Ginkgo seedling 2b

Unless I am mistaken, this is a ginkgo seedling. The closest female ginkgo trees I know of are a half mile away, on Mayslake’s Peabody Mansion grounds, though there is a residential neighborhood just west of the friary that might have others. Their fruits are notoriously smelly to us, but apparently were acceptable as food to a bird.

Among the most recent flowers to appear are those of the nodding wild onion.

Nodding onion b

I’ll conclude with a couple of species that occur both in open woodlands and in prairies: Culver’s root

Culver's root b

and, most spectacular of the lot, Michigan lily.

Michigan lily 1b

These are few and scattered wherever they occur, so remember to enjoy them in place and resist the temptation to (illegally) pick them. Flowers generally are protected on all forest preserves.

Protean Shieldback

by Carl Strang

Yesterday as I rode my bike through Blackwell Forest Preserve I heard my first protean shieldback songs of the year. The scientific name of this katydid is as musical as its common name: Atlanticus testaceus.

Atlanticus female 2b

This is our only common native species of predaceous katydid. We also have a common non-native species, Roesel’s katydid, which I will feature soon. They are called predaceous katydids, but the main point is that they draw their nutrients from animal, rather than plant foods. They are scavengers as well as predators. Protean shieldbacks were very abundant two springs ago, during the periodical cicada emergence. In part this is because they fed well by scavenging dead cicadas, but they probably also benefited from their predators being sated on cicadas. Their carnivorous diet allows them to mature faster than their vegetarian relatives, and so they are the earliest katydids to sing each year (though the common meadow katydid is not far behind).

Protean shieldbacks don’t usually venture far from woody plants, and are fairly common in woodlands, woodland edges and brushy areas in DuPage County. I have found them in grassy fields with dense tall herbaceous plants, too. The males sing from late afternoon until well after dark. Their song is a soft rattling buzz, moderately high pitched, lasting 1-6 seconds. The sound quality is like a stage whisper, I would render it a rapid “thithithith…” about twice as fast as I can produce vocally. For a sound recording, go here  or here . Their season isn’t long; they will be done by mid-July.

Periodical Cicada Behavior

by Carl Strang


This post will conclude my account of periodical cicadas in DuPage County, Illinois, during the 2007 emergence. I had read as much as I could find, from the scientific and popular literature, regarding these insects, but there is no substitute for direct experience. It’s one thing to read that the choruses of singing males are loud, it’s quite another to find that you have to wear ear plugs during lunch time excursions because of concern that hearing damage might result from walking under chorus trees.




With that caveat, of course the literature described things well enough, for the most part. There are no absolutes, though, when you are talking about millions of individuals of any animal. Yes, they mainly came out at night. But some came out during the day, especially on rainy days. There were appalling numbers that became stuck and did not complete their emergence. These died half out of their nymphal skins, or sometimes simply had deformed wings and could not fly. I saw crinkle-winged females laying eggs, though. With numbers so great, finding a mate was easy, and so there appeared to be less selection against developmental deformities than you might expect.


Crinkle-winged female laying eggs

Crinkle-winged female laying eggs





I went out a few nights to observe emergence. On one cool night I heard rustling in the leaves on the ground, but nothing happened, and things quieted down. On a warmer night, the rustling proceeded to hordes of nymphs climbing plants to complete development to their final adult form.




The cicadas usually were quiet through the night and into the next morning, most flying into the tree canopies by mid-day following their emergence. I’m really just sketching here, there is so much that has to be observed first hand. Let me jump ahead to the most unexpected behavior of all.


The cicadas had been out for a couple weeks, perhaps, and had proved to be conservative in their movements. I found that, at the edges of main emergence areas, I could find choruses of males singing 100-200 meters farther out. They flew around some, but did not fly into the open.


Then suddenly, over a period of three days or so, all of this changed radically. Cicadas were flying out into the open, across wide highway corridors for example. After that brief period, small choruses of males were singing all over the county, even in areas where there had been no emergence. I found females in some of those places, too.


Emergence holes

Emergence holes





This was unexpected, and exciting. I didn’t recall seeing anything about this in the literature. So, what does it mean? Is this something that always happens? If so, it doesn’t mean much in terms of cicada populations. These adventurers will have no long term impact if they leave no descendents. But what if this was a unique event, brought about by some fortunate confluence of environmental conditions with a population that had reached a cusp from which large-scale expansion suddenly was possible? If the latter is true, there will be a radical change between the 2007 map and what will be observed in 2024. But, sigh, all we can do now is wait. The next generation is under ground, now, entering its 4-year dormancy at this point, continuing its slow count of years until the time is right for the next round of inquiries into the mysteries of the periodical cicada emergence in northeastern Illinois.

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