When Prairies Provide

Insect life graces planted prairies, even at this time of year -- hiding in stems (and other places), waiting for warmth to return.

My friend and collaborator MJ Hatfield recently issued an invitation to Iowa naturalist-types: Would you be interested in investigating the insect life in a planted prairie near you?

Part of my insect natural history work in the last couple of years has involved hunting for bugs in prairie -- but I usually search remnant prairies, those few rocky slopes and soggy fields from which native prairie plants were never evicted.  I am fascinated by the question of what little-known insects might persist in these remnants, living out their lives in age-old relationship with their now-scarce host plants.

It's been an interesting path of discovery, and I intend to continue it...AND MJ's invitation was also just too good for me to turn down.  Her insect natural history studies have for years included both remnant and planted (or reconstructed) prairies, mostly in Iowa and Minnesota -- and her work in reconstructions has shown clearly that these places do harbor native insects, including specialists that require native prairie plants for their survival.  Research led by Kirk Larsen at Luther College is another local example of work that's shedding light on the insect life in northeastern Iowa's planted prairies.

At the same time, there's a lot still to learn.  While reconstructed prairies are becoming more and more common -- consider Decorah's own Anderson Prairie and Community Prairie -- our understanding of their insect fauna, generally speaking, is quite poor.  In most cases we know very little about how this whole prairie reconstruction thing is working out for native insects.  So it's a good thing that MJ's invitation garnered at least ten "yes!" responses.  As each of us respondees hunts bugs in a planted prairie near us -- which we will be doing without pay, on our own time, mind you -- we'll share what we find with one another and on Bugguide, and hopefully in other outlets too.  In this post, I'll be sharing my findings from a recent walk at Decorah's Community Prairie.

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It was a dreary afternoon for a walk through the Community Prairie.  A thaw was on, and moisture hung thickly in the still air -- but it was a cold sort of wet, clammy and dank.  I dressed in many layers.

First item of business: checking the dead stems (or culms) of big bluestem for a little yellow grub.  Last winter I found these "grubs" -- the larvae of a delightful, iridescent green, long-legged fly -- waiting out the cold in tunnels they'd drilled (with their mouthparts!) through big bluestem culms in a nearby remnant prairie.  They belong to a genus known scientifically as Thrypticus. With various other larvae of moths, beetles, flies, sawflies, and more, Thrypticus in turn belongs to the informal and surprisingly diverse clan of stem borers -- animals that feed on the whitish, spongy pith inside stems of herbaceous plants.

As it happened, some dead culms of big bluestem stood at attention right beside the wooden Community Prairie entrance sign.  The first one I cut open had nothing inside.  But the second culm had been tunnelled...

 ...and it was a good thing I cut it off at ground level, because there, inside the very base of the culm, dwelled my quarry.  Here is is, posed on the tip of my index finger.

In the spring this animal pupates inside the dead grass culm and soon thereafter emerges as an adult fly:

Isn't she lovely?  In spring 2017 this female came out of one of those big bluestem culms I gathered from the remnant prairie.  Here is her pupal skin, still lodged in the culm whence she emerged:

Check out those spines!

You can see more images here (scroll down for clickable thumbnails).  That Bugguide post grabbed the attention of some researchers at NYU who are studying eye development in flies -- and now Fleur, Claude, and I, along with Keith, an amateur entomologist in Illinois, have teamed up in an effort to better understand where to find these flies as larvae.  (My recent finding of Thrypticus in culms of Virginia wild rye, Elymus virginicus, at Chattahoochie Park in Decorah adds to the local list of known host plants.)

Speaking of which...since Canada wild rye, Elymus canadensis, grows in abundance at the Community Prairie, I thought I'd check that for Thrypticus, too.  In this grass I didn't find any little yellow grubs, sadly...but I did find a little whitish one:

This looks somewhat similar to a Thrypticus larva, but there are noticeable differences -- especially the mouthparts.  You can clearly see this creature's two opposing mandibles in the second photo above; Thrypticus wouldn't have this. Our little whitish grub is probably a larval beetle or wasp -- and I'm leaning toward wasp, since I can't see any legs (Bugguide notes that "most [larvae of wasps and their relatives] are grub-like, lacking legs").  Its exact identity will likely remain a mystery until someone is able to rear it to adulthood.

Walking further into the prairie, I came upon seedheads of ironweed, Vernonia fasciculata.  This tall composite adds rich hues of golden brown to the winter prairiescape.

One ironweed stem hosted a short row of closely-spaced holes:

This is where a female insect, probably a tree cricket, inserted her ovipositor in order to lay a series of eggs in the stem.  When you break open an affected stem in such a place, you can see the eggs inside:

Follow this link for a rare and intimate portrait of a hatchling tree cricket in the process of emerging from its egg.

Next stop: Cup-plant!  Also known as Silphium perfoliatum.  There are patches of this plant scattered throughout the Community Prairie, their pale dead stems all splayed out:

And guess what?  My eye caught a sign on this plant that you readers may recognize:

That's right...here, as in "A smart bunch, part 1" and part 2, an enterprising bird has been hunting and pecking (so to speak) for something overwintering inside the stem.  Not sure what that "something" might be, I started breaking open stems to investigate.  Right away, in another cup-plant stem other than the one shown above, I found an insect you may find familiar:

Little chambers in the pith, each with a grub inside...just as in wild lettuce:

Aulacidea sp. gall wasp in stem of Lactuca biennis, wild lettuce

The chamber-grubs in wild lettuce and in cup-plant are closely related.  They are both gall wasps -- just different species, each one adapted to life in its particular host plant.  Actually, I hear there are multiple species of gall wasp known from plants in the genus Silphium; here's MJ's Bugguide series showing adults she reared from this host.

Interestingly, although the wild lettuce gall wasps are clearly targeted by hungry birds, I didn't see any evidence that the cup-plant gall wasps at the Community Prairie are being similarly targeted.  Instead, the birds seem to be looking for another quarry.  That stem with the bird-holes I showed you a minute ago?  It had a total of 14 such holes in it, spread out over quite a distance.  The most thorough pecking seemed to be concentrated on a portion of stem that had been hollowed out by some kind of stem borer.  Here, you can see the bird-holes, opening into the tunnel made by the mystery borer.

I should pause to say that not all hollow or hollow-ish cup-plant stems have been hollowed out by an insect.  Cup-plant's winter stems seem to be variably solid by nature: some are filled with pith, others are mostly hollow...and this can vary even in different parts of a single stem.  Here's a cross-section of a mostly hollow stem that's just naturally that way:

Distinguishing a "natural" hollow from a borer tunnel isn't always easy. In this case, I found that the borer tunnels could be identified by discoloration and especially by the presence of crumbly poop (frass):

Now cup-plant stems are pretty thick, and this tunnel is wide and crammed with LOTS of frass -- so I deduced that the borer must be pretty large (for a stem-dwelling insect).  Of course, in this case the bird had found its prey, extricated it from its tunnel, and eaten it, so I was out of luck...but not for long.  A neighboring stem was similarly tunneled, and the birds hadn't gotten to it yet -- and I was fortunate enough to open it up next, and find this inside:

How's THAT for a tasty bird-morsel?

Judging by the slightly swollen thorax, well-defined head, and lack of obvious prolegs, I think this is a beetle larva, but I'm not sure.  Its color seems "off" to me, suspicious, like the larva might be unwell...so I'm not particularly optimistic about getting an adult.  But I did reintroduce it to a cup plant stem and bring it home for rearing.  We'll see what happens.

After finding this, I spent a while hunting other nearby patches of cup-plant for bird-holes and borer tunnels.  In the end I found only three or four stems that had clearly been pecked up by birds, and I wasn't able to find any more intact stems with borer larvae still inside.  So it's not clear to me how widespread the bird sign or the insect prey may be.  However, you can bet I'll be watching the next patch of cup-plant I come across -- and I hope you do too!

On my way back to the car, as darkness arrived, I scored one last insect sighting:

This is a stem gall on indigo bush (Amorpha fruticosa), a native shrub.  In past visits to the Community Prairie, I'd looked for this gall to no avail -- so I was surprised and pleased to find it this time.  If you cut it open you would find a sizable larva overwintering inside -- a moth larva, specifically, belonging to the genus Walshia.  You can also find similar galls on indigo bush's congener, leadplant (Amorpha canescens).  As with most other larval insects found in stems at this time of year, Walshia caterpillars will pupate sometime in the spring and emerge as adults shortly thereafter.

Incidentally, the foliage of indigo bush can be easily confused with that of black locust, a thorny tree that has been attempting to establish itself in the Community Prairie.  Volunteers have spent a lot of time removing locust from this site -- and they are to be commended for recognizing indigo bush as a different (and less aggressive) plant and letting it be.

All for now!

Nooks and crannies

Meadow Farm, an off-the-grid neo-homestead and locally beloved place, has long hosted a wild bird feeding station in one form or another.  When two housemates and I lived there for several months in 2016, I enjoyed building a few feeders, filling them with black oil sunflower seed, and watching the ensuing "bird TV."  At that time, a curious quirk in some of the birds' feeding habits caught my attention.  I recently returned to find out if it was still "a thing."

Much of the bird activity there centers around a small tree just outside the bank of dining room windows.  It's a convenient place to hang feeders and a comfortable staging area for hungry feeder visitors.  Here's the tree just the other day, with my friend Klaus, who's currently living at the farm:

Before heading outside to take the photos in this post, Klaus and I sat inside and watched the feeders for a little while.  Sure enough, we saw a downy woodpecker and a white-breasted nuthatch doing just what I remembered these species doing at the feeders in 2016.  They had a special relationship with the feeder tree -- one that enabled them easily and fully to exploit the sunflower seed resource being offered to them.

If you look closely at the trunk of the tree,  you'll see a little hollow in the bark:

Now look closer:

Yep, that's the hull of a sunflower seed.  You might also notice little whitish bits of debris -- crumbs of sunflower seed left behind from many a meal eaten here.

As Klaus and I watched from inside, a downy woodpecker collected a seed from one of the feeders, flew to the trunk of the tree, and promptly scooted over to this little hollow.  It deposited the seed here, then proceeded to whack away at it with its bill until the seed hull cracked open, revealing the good stuff within.  The downy gobbled up the tasty "meat" and then returned to the feeder for another seed.

We saw this woodpecker make similar use of another little divet in the bark, a little higher on the tree, above where the trunk forks.  At this place on the tree, our clever woodpecker actually had its choice of three or four such spots:

Here's a closeup of one of them, littered with seed crumbs and pieces of hull:

And another, this one with a leftover hull that someone pecked open just enough to extract the meat:

On a different limb of the tree, a white-breasted nuthatch found a similar hollow.

Because of the shape of this cavity, and the way the bird placed the seed in it, the bird was able to open the seed by pecking at it from two different sides, positioning itself first to the right of the cavity, then to the left, and so on, wham-wham-whamming until the task was accomplished.

We human observers were impressed.  It was fun then to go out to the tree and inspect these nooks, noticing the details that indicated how well they were used.  You know the look and feel of a well-used piece of wood?  Polished by the touch and grip of thousands of hands?

(The less used post, at right, just isn't the same).  Well, the birds' bark-hollows had a similar look.  It seemed to me they'd been used this way for a long time.

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Birds employ different strategies for opening seeds.  Grosbeaks and finches, with their thick, powerful beaks, simply crush the hulls -- as we do with our molars, when feasting on those salty jumbo sunflower seeds.  (If you closely watch a cardinal, for instance, you can even see it manipulate the crushed seed with its tongue to separate the meat from the hull.)  Chickadees and titmice place a seed snugly between their feet on a perch, and hammer at it there until the hull splits open.  But woodpeckers and nuthatches aren't equipped for either of these methods.  As we saw at Meadow Farm, they do something else -- and certainly it doesn't always involve a favorite divet used over and over.  Presumably, just about any crevice will do.  But next time you're watching these birds at your feeder, try to see where they go with their seeds.  I'd be interested to know if your downies and nuthatches, too, have particular places they like to eat!

And if they do -- if this is a widespread practice -- we might be tempted to label it tool use.  Since Jane Goodall's 1960 discovery that chimpanzees "fish" for termites with twigs and blades of grass, biologists have known that humans aren't the only tool users.  Many animals are now recognized for their ability to manipulate objects from their environment to gather food or accomplish other tasks.  May we call a bark-hollow such a tool?  It's not really something you can grasp, or wield, or move.  But there's something special about it.  The birds have a relationship with it.  They go to it.  They use it repeatedly.  They appear to have shaped it -- by smoothing it, and perhaps, over time, by widening or deepening it.  And without them, it would not be used in the way it is.

To me, there is a sense that, in a small way, the downies and nuthatches have sanctified that Meadow Farm feeder tree with their habits.  They have made it unique, and that uniqueness is relational: defined in and by community, where, we might argue, sacredness always dwells.  Life is always inspiring us and challenging us with its depth and breadth of relationship.  It touches everything -- and everything is changed forever as a result.

I pray that we may feel with our hearts these changes, big and small -- and know them as signposts of the Spirit in things.

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NOTES

Credit is due to friends Lee and Lindy for introducing to me the phrase "bird TV."

A smart bunch, part 2

A thought inspired by the loveliness of this blue-sky January day:

What I lack is a context for beauty.
What does it mean, that the world is this beautiful?
What do we do, given that the world is this beautiful?

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In part 1 of this post, we considered a few examples of bird sign on dead wood and on stems of two herbaceous plants, figwort and jewelweed.  Here we'll see examples from the stems of two other herbs.




COW PARSNIP

Heracleum maximum is a sort of coarser, jollier, more badass cousin to the ubiquitous wild parsnip (Pastinaca sativa).  Cow parsnip and wild parsnip are easier to tell apart during the growing season, but there are obvious differences between their dead stems in the dormant season too.  Above, you can see a dead stem of wild parsnip on the left, and one of cow parsnip on the right.  Below, fruits: wild parsnip at left, cow parsnip at right.

While visiting some friends early this past summer, I noticed that stems of the cow parsnip growing in their yard had been attacked heavily by some critter trying to get in.  It wasn't until many months and two seasons later that I finally returned to Lindy and Lee's in order to document this damage.  The plant stems, long since dead and dried, had broken off and fallen to the ground, and some were buried by snow, but I gathered what I could.  The attackers' work was still evident.

Now, as with jewelweed, the scientist in me insists on mentioning that I have not directly observed the animal responsible for this.  However, based mostly on the form and appearance of the holes, I assert here that a bird is responsible.  Someday one of us will catch the culprit in the act!

Unlike jewelweed and figwort, the target insect does not overwinter in the stem.  Rather, its stem-dwelling stage -- the larva and pupa -- occurs in the late spring and early summer, when cow parsnip is maturing (and right around the time I first saw damage to these stems at Lindy and Lee's).  This insect is the parsnip webworm, Depressaria radiella.  Though named, and thus clearly known, for its habit of spinning webs in the flower heads of cow parsnip and wild parsnip, some larvae of the parsnip webworm enter their host plant's stems, which, for cow parsnip at least, are naturally hollow.  (Presumably the larvae cut holes in the stems in order to get in and out; this could account for a few of the stem holes evident in the first stem-damage photo above.)  Furthermore, some of the larvae will actually pupate inside the stems -- and I suspect it's this pupal stage that the predators were after in the plants at Lindy and Lee's.

Before pupating inside its dark and hollow stem-home, a parsnip webworm larva apparently first etches an oval scrape on the inside of the stem.  The larva either eats this excavated material, converting it to frass (caterpillar poop), or simply shaves it off the stem, resulting in an accumulation of sawdust.  Either way, it collects the granular byproduct and incorporates it into a domelike cocoon, which it spins over itself just prior to pupating.  The results (but with the culprits long gone) are shown below.

First, a piece of stem interior on which four larvae pupated.  The most obvious oval scraped areas are on the far left and far right; two more are clustered at center.  I've removed the domed cocoons that were spun over three of the scraped areas; the fourth cocoon (at far left) has been flipped over to reveal the scraping underneath it.

 

 Two cocoons, one in the top stem, one in the bottom stem (and part of a third cocoon, I think, at upper right).  Larvae scraped the stem underneath these cocoons,  processed it into "sawdust" or frass, and finally incorporated it into the cocoons.

 

 Cocoon

 Wall of cocoon flipped over, revealing shed skins of larva and pupa, indicating successful emergence of an adult moth

 Detail from inside the above cocoon, taken with my "bug scope."  After spinning the cocoon (top), the larva sheds its skin (right) to become a pupa.  When the adult eventually emerges from the pupa, it leaves the pupal skin behind (left).  (And by "skin," I mean exoskeleton.)

Here's a sequence showing another cocoon, its leftover (spent) contents, and the adult that emerged from it:

The adult's wings are improperly formed in this case.

If this moth looks vaguely familiar, it may be because you've seen it in your house!  I saw one in my bathroom last week.  And, under her image of a nice adult specimen on Bugguide, my friend and collaborator MJ Hatfield writes, "Yes, there is a lot of parsnip in the neighborhood.  But still, why do more of these show up in the house than any other moth?  Perhaps under bark of firewood? I don't know."  Neither do I, MJ!

WILD LETTUCE

One winter day, while visiting friends John and Jana, I heard someone a-tap-tap-tapping away in the yard over by the guest cabin.  It was unquestionably a woodpecker, but the tapping had a sort of treble quality to it that suggested the bird was tapping on something other than wood.  Walking over to investigate, I frightened a downy woodpecker from a dead stem of a tall, weedy herb.  The stem belonged to a wild lettuce, Lactuca biennis.  Here's a different stem of the same plant species, also from John and Jana's, with the author attempting to provide scale but mainly just looking like a super dork.  As you can see, this herb gets to be quite tall!

Seedhead of Lactuca biennis, with most of the seeds already gone

Well, when I got close to examine the downy woodpecker's wild lettuce stem, I was astonished and delighted at what I found.  A significant portion of the plant stem had been stripped or pecked away.  (I stripped away more as I investigated, then took the photo below.)  This activity had exposed the pale inner pith of the hollow stem, and this exposed pith, all up and down the stem, had been thoroughly pecked over by birds.  Below, the whole dead stem is shown (at left), along with two details of affected portions (at right).

Here's a detail of an affected area near the base of the stem:

At first, I thought all those brown specks were simply peck marks left by birds.  As I looked closer, I noted that the birds had indeed excavated the pith in these areas.  But their pecking hadn't caused the brown specks.  In fact, the "specks" were little round chambers in the pith, hundreds of them, each one emptied by the birds of whatever had been inside it.

To illustrate what I mean, here's another dead stem of a wild lettuce plant attacked by hungry birds.  I found this one on a property in Clayton County, IA where friends Joe, Conor, and I spent some time last year.

As they peck and probe the pith, the birds' bills leave small indentations (labeled, at center of inset).  However, this sign is quite distinct from the brown "specks" -- more clearly identifiable here as chambers (see label at upper right of inset) -- that are constructed in the pith by the insect that the birds are harvesting.  As it turns out, before it gets raided by a bird, each of these little brownish chambers contains a single cream-colored insect larva:

This is the larva of a tiny, black, non-stinging wasp in the family Cynipidae.  Animals of this kind are known as "gall wasps" for their habit of growing to maturity inside the swellings they induce in plant tissue.  Not all plants affected by gall wasps show obvious swelling; this one didn't.  However, the tattered wild lettuce stem at John and Jana's did have some galls on one spot along its length:

The birds, of course, noticed.

 A cross-section of the swollen stem reveals two gall wasp chambers (arrrows).  I think the larvae fell out when I cut the stem open, which is why they aren't visible here.

Another gall on the stem, sectioned, showing larvae in their chambers

At the time, I didn't know exactly what this insect was, so I collected a few pieces of affected stem from John and Jana's and put them in a jar.  That was early April; by late May, adult gall wasps in the genus Aulacidea had begun to emerge.

These images, of a point-mounted adult in less than ideal lighting, really don't do it justice, though.  This is a lovely creature with which we are fortunate to share this Earth (and, honestly, it's kind of sad to see it dead in these photos I took!).  I wouldn't have known about it were it not for that enterprising downy woodpecker, so the bird deserves my gratitude too.

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A final note: When I came across this bird-insect-plant association, it wasn't just the insect I couldn't identify; I wasn't quite sure about the plant, either.  As you might expect, identifying plants by their dead stems can be challenging.  However, it's been so useful to me as an amateur entomologist that I have spent the last few dormant seasons learning to do it, and it's not only possible, but also satisfying and enlightening.  Along the way I've picked up a trick or two.  One of these involves the leaves.

Though many flowering plants shed their leaves in fall, some leaves stay attached, especially on certain herbaceous plants, where they simply shrivel up and hang from the stems.  If the dead stem of a mystery herb has any such leaves still hanging on, try collecting a few of them (carefully, as they are quite fragile) and placing them in a shallow, flat-bottomed container of water.  The shriveled leaves will gradually rehydrate, and once they're waterlogged, you can (carefully) use a toothpick or other tool to gently pull them open and flatten them out (while they're still in the water, ideally).  This will reveal the general shape, veination, and other details of the leaf useful for making an identification.

I tried this rehydrated leaf method with a few leaves from the then-mystery plant occupied by the then-mystery insect at John and Jana's.  Here's the result:

Compare with the image here of a living leaf of Lactuca biennis.  It takes a bit of effort and patience, but this method works!