Wanted: A Few Good Herbivores

If you encounter a book or article that claims that, surprise!, invasive species aren't such a big problem after all (a few were written over the past decade), you'll probably find no mention of herbivory. They'll say that invasive plants are being falsely maligned, because actually they do wonderful things, like provide berries and nectar for wildlife. But it's to the plant's advantage to have its flowers visited and its berries consumed. What the plant doesn't "want" is to be eaten, and therein lies the problem with plants that become invasive. For whatever reason, be it an invasive's chemical defenses or ingrained dietary habits, the wildlife tend not to eat them.

Nature depends on consumption to keep things in balance. We love nature for its beauty and variety, but behind the scenes there's a whole lot of mastication going on. Take away predators and the deer population explodes. Introduce a new plant that the wildlife won't eat, and there's potential for that species to make habitat less and less edible as it displaces the natives. To fill this void in consumption, people have had to play the role of herbivores. What we do at Herrontown Woods, as we cut down dense groves of winged euonymus and other nonnative invasive shrubs, is to play the role of the missing herbivores, using our loppers for teeth.

There's some pleasure in the work--pleasing vistas created, serendipitous discoveries. But all things being equal, it would really be nice if the resident wildlife could show some flexibility in food preferences and fill the void in consumption. Invasives, after all, represent a huge, untapped food source for any animal willing and able to broaden its palette.

Given how much work it would be for humans to play the role of herbivores in the forest, any evidence of wildlife gaining an appetite for invasive plants stirs some hopefulness.

For instance, an invasive honeysuckle shrub was recently found stripped of its leaves. A closer look revealed something had been hard at work, its mandibles outshining our loppers: the caterpillar of a snowberry clearwing moth, also known as the "hummingbird moth" or "flying lobster", for its capacity to hover in front of flowers as it sips their nectar. Maybe if we had more summer wildflowers for the adult moths to feed from, their caterpillars would help control the populations of bush honeysuckle in Princeton's preserves. Nice to think, anyway.

And what's this orange plant growing on a dense expanse of invasive mugwort that grows as a monoculture along the gas pipeline right of way in Herrontown Woods? Dodder is a parasitic plant with little capacity to gather energy from the sun. Instead, it wraps itself around other plants and sucks out their juices.

Usually, its impact is small, but this must have been a particularly good year, because a sizeable patch of mugwort was sucked dry.

If only we could get the dodder (genus Cuscate) to preferentially neutralize the mugwort all along the right of way, some diversity might return. Again, a nice thought and tall order.

A new invasive trying to gain a foothold in Princeton is mile-a-minute vine, with a distinctive triangular leaf, a prickly stem, and a growth habit to match its name. Another post shows how invasive this annual vine can be , on farms just outside of town. Fortunately, after weeding out a small population back in 2007, I know of only two patches currently growing in Princeton, still small enough to control and hopefully eliminate altogether.

One's at the Princeton Battlefield. This year's growth was pulled out in early summer, and when checked in late August, the patch had only managed to produce a few leaves, all of which were being very effectively munched on by a weevil intentionally introduced to the U.S. to bring this rampant new species under control.

Ah, I concluded, to control mile-a-minute vine, simply reduce the patch in early summer, leaving enough for the weevils to sustain their population on. Their appetites appeared to be sufficient to prevent any flowering or fruiting that could lead to the patch spreading elsewhere.

Nice concept, but it wasn't working at the other site, down along the driveway into Rogers Refuge, where the vine had sprung back up, flowered and fruited, undeterred by the minor nibblings of the weevil. That patch had to again be pulled out by hand.

Another discovery was the work of the Ailanthus webworm moth, which had completely defoliated a young tree of heaven near the parking lot of Herrontown Woods. The moth, like the tree, is an introduced species.

If you have flowers like boneset growing in your backyard, you may be helping the adult moths to prosper.

Here again, though, the larvae have thus far been seen only on very young trees, with larger ones largely left untouched.

These are glimmers of hope, sprinkled across Princeton. It will take some concerted mastication by as yet unnamed herbivores to stem the tide of rapidly spreading species like porcelainberry, callery pear and stiltgrass--a giant uneaten salad that grows by the year. A little salt and pepper, perhaps?

The Viburnum Leaf Beetle's Gathering Harm

This fall, before the leaves fall off, check any Viburnum shrubs you know and love, whether in your yard or in your favorite nature preserve. Do the leaves look like this, pitted with holes, or even stripped down to the veins?

Most people have heard by now about the Emerald Ash Borer's rapidly multiplying demolition of our ash trees. Lest that devastation not be enough ecological and horticultural tragedy to absorb, there is another invasion underway in Princeton, by the Viburnum leaf beetle. This one--a European insect that first showed up in Canada before spreading to the U.S., is going after our understory, one Viburnum species at a time.

This and the above photo are of Viburnum dentatum, the arrowwood Viburnum, which grows here and there in our woodlands, preferring wetter soils. The light damage could have been done by a native insect, or by the first few Viburnum leaf beetles to show up, suggesting much greater damage the next year. Listed as "highly susceptible" on Cornell's website, the arrowwood Viburnum will be the first to succumb.

The maple leafed viburnum, frequently encountered along the Princeton ridge, is less susceptible and thus isn't showing any damage this year. As the Viburnum leaf beetle increases in numbers and exhausts the most susceptible species through complete defoliation, it will presumably begin attacking those that are less susceptible.

We are not completely helpless as yet another careless introduction to the continent wreaks slow motion havoc. This site offers some ways to prevent the beetles and their larvae from consuming your favorite specimens. As with all environmental damage done, the ecological and aesthetic services these shrubs were providing for free will now start coming with a price tag for human maintenance.

The Cornell site offers another ray of hope. An extension official in Rochester, NY asserts that even highly susceptible species may in the long term become viable again, as predatory insects and soil nematodes build up to prey on the Viburnum leaf beetles. Then, perhaps, the introduced species would come into some sort of ecological balance, doing some damage but not enough to kill the Viburnums.

It's a perfectly logical and reassuring scenario, and yet observation often brings into question the speed and effectiveness of nature's capacity to restore balance and sustain diversity. More often, invasive species remain dominant and destructive, be they Phragmitis, or Japanese stiltgrass, or porcelainberry. I called up the Frick Park Environmental Center in Pittsburgh, where I had first witnessed the devastating impact of Viburnum leaf beetle a decade ago. Asked whether they had seen any signs of balance being restored, they answered, "Not yet."

Related links:

The Pennsylvania extension service also has some useful information.

Past NatureNotes posts about the Viburnum leaf beetle, dating back to 2013, can be found here.

This post explores the likely aftermath of the Emerald Ash Borer invasion currently underway.

Stalking Monarchs, and Encountering the Other Milkweed Caterpillar

Note: This post serves as a contrast to the horrific flooding in Houston from Hurricane Harvey, showing how stormwater can drive diversity rather than destruction, if we work with nature rather than against it. Unlike cities, the plants that grow in floodplains are built to pop back up within days or hours after a flood and just keep on growing and flowering. Most of these photos were taken in a detention basin, which is an acre-sized depression in the ground, dug to receive storm runoff from the Smoyer Park parking lot. The purpose is to "detain" the rain that hits the asphalt and that would otherwise rush into the nearby stream. Detaining the water reduces flooding in downstream neighborhoods. The detained water then either seeps into the ground or is slowly released through a small pipe into the stream after the floods have receded. 

Last year, a collaboration of federal and local governments with the Friends of Herrontown Woods converted this mowed basin into a wet meadow with floodplain plant species that thrive with these periodic pulses of runoff. Without regulations requiring it, the concave setting for this lovely oasis for native plants and pollinators would not exist, and the polluted runoff from the parking lot would have flowed straight into the local stream, contributing to flash floods.

Nature has offered up some surprises, here in the doldrums of summer, when people who aren't somewhere else sometimes feel like they should be. There was the unexpected, and unexpectedly affecting, chance to capture family portraits of black vultures in the previous posts; the weather has been unexpectedly cool; rains have come when needed for the third year in a row, and monarchs have proved resilient, rebounding from their diminishing numbers in recent years. Not many, as yet, but more.

Thinking them elusive creatures, I figured a zoom lens was necessary to capture their image. First came a peekaboo shot on the far side of a thistle at the Smoyer Park detention basin that we converted last year to (mostly) native meadow.

The blooms of Indian grass got pleasantly in the way of this shot.

With nowhere else to go in a sea of soccer and baseball fields, the monarch kept circling around the planted meadow, encouraging patient waiting for a chance at an unobstructed view. Finally, a clear shot from 100 feet away, while it perched briefly on a river birch. Congratulating myself on some success with a powerful camera, I plunged into the meadow to weed out a small clump of foxtail grass that would become way too numerous if allowed to go to seed.

And there, five feet away from my tugging and clipping, landed the monarch, easily photographed with an iPhone,

with a coppery background of Indian grass. That's what weeding a wild garden does--it immerses the gardener, creating opportunities for serendipity to work its magic.

Just across Snowden Lane from the park, behind Veblen House where our Friends of Herrontown Woods group has fashioned a clearing by removing invasive shrubs and wisteria, another sort of caterpillar munched on the leaves of common milkweed, which has prospered in the resulting sunlight.

Displaying proper Princeton colors, the milkweed tiger moth needed every milkweed plant there, and then some. We came back a week later and found every milkweed stripped down to bare stems. The common milkweed's strategy of aggressive underground spreading becomes more understandable, given the voracious appetites of these caterpillars.

Also called the milkweed tussock moth, the caterpillars become more colorful as they grow. As an adult moth, they are said to retain the cardiac glycosides they pick up from eating milkweed, and warn bats of their unpalatability by emitting a click as they fly about at night.

With summer almost over, a first sighting of a monarch larvae--on a purple milkweed, of which there are very few in Princeton, for some reason. Common milkweed can be a bit too aggressive in a garden, and swamp milkweed disappeared from our garden after a few years. Purple milkweed with its showy blooms may be a good alternative, if we can find any seed after the hungry caterpillar is done.

Nature Caught Spying on Nature Writer

All NatureNotes posts should be so easy.

A typical-seeming photo of my desk

that turns out not to be so typical after all.

Good morning, praying mantis, and welcome. Care for some coffee, or are you here to keep an eye on me?


Update: What a praying mantis was doing indoors, and how it might survive, was not immediately obvious. Later in the day, however, during a recording session, a musical "B", slightly out of tune with my guitar, was heard emanating from somewhere on the desk. It was finally tracked down, and turned out to be a fly making the tone of a "B" while having its head eaten by the praying mantis.

Slapstick Cicada

This past week, as hot weather warmed the ground, cicadas emerged in their clown-like skins, with red eyes instead of red noses. Nature sightings can come in a moment of leisure, and this one came while sitting for a few minutes on the front step Friday afternoon. A few yards away, an adult cicada was crossing the stone walk, as determined as it was awkward, each tiny stick or leaf fragment presenting a formidable obstruction to progress for its bulky body. When it reached the garden bed, it clambered in and around the leaves, finally choosing a spent flower stalk as substrate for its vertical ambitions. With clumsy zeal, it climbed the narrow, flagpole-like flower stalk of a wood hyacinth. As it approached the top, the stem bent, so that by the time it reached the tip, the tip had tipped over and was no longer the top. The cicada, knowing up from down and desiring up above all, turned around and headed back up what moments before had been down. Relieved of the cicada's weight, the tip then straightened back up, leaving the cicada once again below the top. This could have gone on for quite awhile, as if the cicada had been born into a slapstick movie from the Buster Keaton/Charlie Chaplin era, with our frontyard serving as movie set.

Numerous on the leaves of the nearby frontyard raingarden were the spent skins from which the adults had emerged overnight. It's a beautiful transformation if you ever chance upon it.

Not being an entomologist, I can attest only to what I've read, that since these are emerging in spring, they must be the periodical cicadas--those that appear every 13 or 17 years en masse--a phenomenon unique to eastern North America. Annual cicadas, by contrast, emerge in summer and are found worldwide.

Perhaps the cicada, so intent on climbing, was seeking a good perch to sun itself, the better to harden its exoskeleton over the next few days.

We'll see if all this clambering gives rise to a great clamor in coming weeks.


Past posts on the subject can be found by typing "cicada" into the search box. Here are a few:

Cicadas "Clean up real good"
Cicada killers living peacefully among us
Struggle for Survival--Scene 1

Searching for Monarchs in Princeton

The monarch butterfly, as most people know, is in trouble, due in part to a radical decimation of milkweed on more than one hundred million acres of farmland in the U.S. in recent years. Thus far this summer, I had seen a grand total of two monarchs, one having visited the raingarden in my front yard on Harrison Street. Another raingarden on Harrison Street, at the Spruce Circle senior housing, had just been bulldozed while in full flower.

With that traumatic step backwards in mind, I set out yesterday on my bike to check out a few spots elsewhere in Princeton. If a monarch were to travel around town at about the speed of a bike, wings warmed by the sun after a recent rain, would it find any prospective mates?

First stop was the meadow at the corner of Mountain Ave and the Great Road. The Joe-Pye-Weed was blooming as it does every year, but no monarchs to be seen.

Then a ride up the Great Road to Farmview Fields, where I had hooked the town up with Partners for Fish and Wildlife--a federal agency--to plant a meadow of warm-season native grasses in a stormwater detention basin that had previously been mowed as turf. More habitat, less mowing. Everyone was happy. I had added some native wildflowers, and others had seeded in. When I checked last year it was doing great. Yesterday, however, I was surprised to find the grasses stunted and the wildflowers gone. It hadn't been bulldozed, but something's wrong with the mowing regime, which should be just once a year during the dormant season.

Again, there's a sign that should signal that this is a special area, requiring a different management.

The heavy equipment had left some patches of ground scarred and bare. Mowing crews are so used to mowing these detention basins elsewhere that they may have started regularly mowing this one, out of habit. I had a job mowing a golf course one summer. It's not the kind of work that encourages thinking outside the box.

An unmowed area nearby showed what the basin should have looked like, with the "turkey feet" of big bluestem rising to the sky.

There was a swallowtail butterfly sampling the basin's meagre offerings, but still no monarchs.

Back down the Great Road to the opening in the fence, near Pretty Brook Rd, to take the boardwalk across the bottom of Coventry Farm over to Mountain Lakes. Lots of common milkweed in the field, but no signs of their being munched on by monarch caterpillars.

Finally, along the boardwalk near a big wet meadow of ironweed (the hydrologic conditions a raingarden imitates), I saw a lone monarch, flying about but not landing. As the monarch numbers have dwindled since the 1990's, the question arises, how do they find each other? They start each year in a small enclave in the mountains of Mexico, then spread out across vast areas of the U.S. and Canada. This migration, with one generation succeeding another as they move northward, is predicated on having sufficient numbers for individuals to find each other and mate. The lone monarch and the uneaten milkweeds offered little reason for optimism.

At Mountain Lakes House, a popular place for weddings and other gatherings, and also home base for Friends of Princeton Open Space, the raingarden I designed was prospering.

Lots of color there,

and in another rain garden in the driveway, but no monarchs to be seen.

There was still one spot to look, though, in the fields of Tusculum, preserved by Friends of Princeton Open Space and others, and packed with milkweed. To get there meant maneuvering through the now tattered evergreen forest of Community Park North. High winds in recent years have knocked down most of the pines and spruce, which really aren't natural to this area but had provided a deep forest feel that was enjoyable to walk through. Now, fallen trees have opened up the canopy, energizing an understory of invasive stiltgrass and honeysuckle.

Some trails are lined by young ash trees that will likely be attacked by the emerald ash borer when it reaches Princeton. This strangest of woods was not feeding optimism either.

The fields of Tusculum also looked different than in past years, perhaps again due to a mowing regime that might not be the best for wildlife habitat. Mountain mint, once a common wildflower there, was nowhere to be seen. And no monarchs.

But then, near Cherry Hill Road, next to a purple patch of tick trefoil and Indian grass,

monarchs, a pair, mating!

They flew over into the meadow to continue. Part naturalist, part voyeur, I lingered, wishing to document how long such pivotal acts take. It became clear that this was no brief rendezvous, so I moved on,

to the next field over, where common milkweed sprawled over more than an acre.  And there, another monarch, showing off its brilliant, speedy flight, ducking in and out among the milkweeds, as if in a hurry yet undecided as to where to land. It did land a few times, briefly, perhaps to lay an egg? I checked the undersides of leaves, but it was hard to tell from a distance where it had landed.

I biked home more hopeful than two hours prior. Those monarchs were starting the last generation of the year, the one that will fly all the way back to Mexico. On the way back, I passed the Princeton High School's detention basin just north of the performing arts center on Walnut Street. Now wouldn't that be a fine gesture, an act of generosity and belief in the future, if the school were to turn that empty, unused basin into a monarch meadow.

A Banner Year for Hickory Nuts, Hicans, Butternuts and Beechnuts

It's easier to dream of what bounty the forest once offered in a year when hickories and hicans are littering the ground with delicious nuts conveniently packaged for longterm storage. These in the photo are hickory nuts, which may trigger memories for some of Euell Gibbons pitching Grapenuts cereal.

In this photo, hicans from a hybrid pecan/hickory tree rub shells with butternuts (Juglans cinerea), also called white walnut. The butternut, particularly one that is pure native and not a hybrid, is fairly rare and made rarer by butternut canker. The canker disease, like so many diseases and insects that threaten our native trees, was likely introduced from another continent.

Some good news on that front is that local expert on nut-bearing trees, Bill Sachs, harvested 80 native butternuts from a local tree this fall, and has planted most of them in a small nursery for spring germination. He has already grown some from previous crops and planted them in various parks and preserves in Princeton, in an effort to help the species rebound in our area.

A good harvest of nuts deserves a good nut cracker--one that exerts pressure on either end so the meats inside don't get smashed in the process.

Given that this blog courageously endeavors not to turn its back on reality, and nature being what it is, there are some other--not particularly appetizing--species that take an interest in the nut crop. This, to me, seems like part of the adventure of real food, as opposed to the factory-like conformity favored on grocery shelves. Open-mindedness, though, is easier if the insects leave a goodly portion of the nuts untouched.

After collecting nuts from the ground, it's best to leave them in a metal bowl for a week or so to allow time for any pecan weevils to emerge. Nuts that don't have the characteristic exit hole should be fine to eat.

Another nut being scattered in Princeton's woodlands is the beech nut. Though it's reportedly edible, word of mouth has not been encouraging, and these in the photo turned out to be empty.

Dragonflies Dazzle in Local Parks

If you're out in a park tomorrow, take a look up in the air.

First, a memory: A couple years ago (will have to check what time of year), I chanced to walk into Potts Park--the little pocket park just off North Harrison Street--to find the sky filled with hundreds of large dragonflies. A closer look revealed that they were feasting on small winged, antlike insects streaming up out of the ground. The dragonflies zigged and zagged, snatching flies from just above the lawn up to sixty feet or so. Above them, in turn, was a flock of swallows trying to catch the dragonflies. A plain park of grass and play equipment had been transformed into a dazzling airborne foodchain of hunters and hunted, all precipitated by the hatching of a colony of insects that had probably been quietly living under our feet the whole summer. The plain lawn proved not so plain after all.

This memory came quickly to mind when today, returning home around 5:30pm, I found a phone message from Peter Wolanin, former collegue on the Princeton Environmental Commission. He had called to tell me dragonflies were swarming in Quarry Park. There had been lots yesterday, but still quite a few today. I got there in time to find about twenty large dragonflies, bluish in tint, flying above the lawn. What, don't you see them in the photo? I had about as much luck photographing their zippings around as the swallows had two years ago catching them for dinner.

There were no swallows this time, but I was able to track down the source of the small insects the dragonflies were catching. They were emerging out of a plain patch of mowed grass and mugwort near a stormdrain.

These, too, were hard to photograph, but you can see their antlike shape and wings. They crawled around on the grass blades until ready to fly. Some appeared much smaller than the others.

They're tiny, but apparently worth the while for the dragonflies. It's a scene not unlike the hatching of sea turtle eggs on a beach, where the baby turtles then have to run the gauntlet from nest to surf before getting snagged by a seagull.

Though the dragonflies' approach could seem helter skelter, they will sometimes assume a very systematic search pattern. Staying head height off the ground, one will fly thirty feet in a straight line, then make two perfect 90 degree turns to return in the opposite direction, exactly parallel to its previous path, offset about five feet. The pattern seldom lasts long before they break it to snag another insect.

A few dragonflies were also found patrolling above Potts Park today, a quarter of a mile away, where a similar hatch must have occurred.

More distant memories of dragonfly swarms were more likely associated with migration, such as when I saw thousands of them flying what must have been north, above the freeway that parallels the shoreline in Chicago.

There are many, many videos of dragonflies swarming on youtube. Here's one from "thedragonflylady."