Where Have All the Pollinators Gone? -- Summer, 2021

Wherein is discussed the season's paucity of pollinators, the curiously prolific presence of hornets, and possible causes thereof. 

With the coming and the going of this year's autumnal equinox, it's time to look back on a long summer and ask, "What happened?" Or, more precisely, "What happened to the happening that didn't happen?" 

There's lots of talk about how insects are in decline and that we need to plant more wildflowers to support them. A local ecologist and avid birder, David Wilcove, co-wrote an oped in the Washington Post about the danger posed by insect decline, and the need to better monitor populations, as is done with birds.

In past years, a summer's climactic buzzfest on the boneset

This year, there was a steep decline in pollinator numbers in Princeton. Each year I grow a banquet of wildflowers in my backyard for all manner of insects to feast upon. In past years, they'd come from near and far, their numbers building through summer, climaxing in late August in a buzzfest on the boneset. Though mountain mint is another great draw for insects, in my yard it was boneset in particular, clustered here and there in the garden, that in past years drew the multitudinous shapes and sizes of the insect world. Its broad disks of tiny white flowers seemed like a Serengeti in miniature, an open plain perched conveniently four feet above the ground, teaming with life. It was a chance to see the insects close up, they being so focused on the nectar or each other that they took little notice of me.

Then, two years ago, and again last year, the numbers of insects were down--still numerous but not enough to stir that late-summer's jazzy feeling of frenzied activity. 

2021: An astonishing diminishment

And this year? This year, boosted by the rains, the wildflowers grew to fabulous size. Broad arrays of blooms mounted on multiple stems stood at the ready. In early summer, while periodical cicadas held center stage, the numbers and variety of pollinators were building nicely. 

But then, as the wildflower meadow's heavy hitters--the cutleaf coneflowers, Joe-Pye-Weeds, bonesets and wild sennas--unveiled their fabulous blooms for the mid-summer festival of nectar, the insects were no-shows. Abundant flowers had few pollinators, and sometimes none at all. Diversity dwindled to some tiny somethings, a few bumblebees and even fewer honey bees. 

Sifting through possible causes for the decline

Possible causes for the dramatic decline have been offered: extreme heat, more homeowners fogging their yards for mosquitoes, expanding monocultures of lawn and invasive species. Or perhaps the climate-changed winters have messed with insect dormancy.

The rains of July, the rains of August

What I have particularly noticed over the past three years, however, is the increase in rain during the summer. Rutgers precipitation data for NJ show increased precipitation particularly over the past two years in July and August. Not only has there been more rain, but the intensity of the rain has increased. The sound on the roof is different--one can hear and even feel the extraordinary density and weight of the rain. The deep trauma of Hurricane Ida was the climax among multiple intense storms before and after. The ground and foliage are literally getting beaten up by these deluges. Insects try to hide during storms. Some live in the ground. The harder the rain, the fewer places to hide, and the more likelihood that a ground nest will be flooded out. All that sustained moisture could increase the risk of disease, which an entomologist friend says can play a big role in bee numbers. 

Some of us noticed other changes as well. Gladly, the numbers of odorous house ants invading our kitchen were down from previous years. Mosquitoes in our area seemed relatively rare in early summer, though numbers surged later in the season--tiny ones, probably asian tiger mosquitoes. 

A proliferation of hornets

What was most striking and very strange was a proliferation of hornets. Last year, I seldom saw them, but oftentimes this summer, approaching a patch of flowers, the first thing that would catch my eye was not pollinators but the hornets that can prey upon them. 

We have two kinds of insects called hornets. One is the European hornet, which looks to me like a stocky bee--black markings with a particularly thick yellow abdomen.

The other is the bald-faced hornet, a native insect with black markings and a whitish face. 

Both are hard to photograph because they don't land, but instead keep cruising around the flowers. Periodically they may bump into a bee that was minding its own business on a flower. The contact lasts a split second, then the hornet flies on. The purpose of this brief harassment is not clear. 

Here's a bald-faced hornet in adult and larval form, found on a fragrant of nest someone left at the curb. Both kinds of hornets live in nests that are in or hang from trees. The paper they make, by the way, is beautiful when looked at close up.

Why the proliferation of hornets, cruising relentlessly among the flowers with a sense of urgency but no clear goal? Maybe they just seemed more numerous due to the lack of other insects to catch one's attention. Or maybe the fact that they live in elevated, waterproof nests allowed them to better survive the intense storms. 

The seeds of change planted over centuries

In any case, this summer was not the lively pollinator party I was used to playing host to, both in my backyard and at our Botanical Art Garden (the "Barden") in Herrontown Woods. One interpretation is that the carbon dioxide we've been scattering to the winds is now coming home to roost, in the form of weird winters and intensified storms. In Princeton, basements flooded that had never flooded before. It's not a stretch to hypothesize that many bees also find themselves newly vulnerable to the merciless power of the rain. And then, on the sunny days when pollinators can make it to the flowers, there's the haunting background of patrolling hornets.

In a docile wasp, some small comfort

As students returned to the university, I remembered helping my daughter move in to Whitman College two years ago. In the courtyard, I had noticed thousands of wasps cruising just above the grass. It was a mating dance, of no danger to the parents and students passing by, of blue-winged wasps. I had recognized their distinctive orange abdomen from those that would frequent the flowers in my backyard, a mile away from campus. 

This year, I had seen only one in my yard, and wondered whether their improbable annual ritual was still playing out at Whitman College. 

What I found on Sept 2nd were perhaps a hundred wasps flying in their usual criss-cross manner a foot above the lawn. Some seemed fatigued by it all, and would abandon their flight to sit among the grass blades for awhile. Though their numbers were down from the thousands I'd seen two years prior, I was glad to see any at all. And a student sitting in a lawn chair, scrutinizing his computer, told me there had been many more ten days prior when students first began moving in. 

It would be nice to think that the paucity of pollinators I observed this summer was an isolated affair. But others around New Jersey have made similar reports. An entomologist friend who lives in Oregon told me that he's seen "a very significant decline in pollinators" this year, probably due to drought, though he also said that each species can vary in numbers year to year. 

An ark is built of something more than flowers

We take so much for granted in our lives. When something breaks, that's when one has to study up and figure out how it works, what went wrong, and how possibly to fix it. The insect world has been taken for granted since forever. Annual bird surveys benefit from a community of avid birders, but citizen scientists who are up to speed on the mind-boggling diversity of insects are fewer to come by. We thought we could just plant some flowers and the insects would come, but the needs appear to be far deeper than that. 

Murder Hornets and Princeton's Cicada Killer

The scary reports about murder hornets offer an opportunity to write about invasive species and insects generally. "Murder hornet" is a nickname, but the insect's real name, Asian giant hornet, is not very reassuring. There have been some scary videos making the rounds. The NY Times article was less sensationalistic, and captured well the potential threat along with the actions being taken to counter it. Rutgers hastened to clarify that the insect isn't found in the northeastern U.S.. And it's still not clear whether the AGH (Asian giant hornet) has established a population in the northwest, and if so whether the population is still small enough to be eradicated.

Big insects are scary. One nightmare remembered from childhood was of an ant about two feet long. I had a memorable bike ride home one day with a wasp having perched on my shoulder. I decided to just let it sit there, and eventually it flew off. The more I learn, though, the less scary most insects become. Late last summer, I waded out into a lawn full of blue-winged wasps flying about, knowing they were harmless. Knowledge can lead to a gentle response to something seemingly dangerous in nature. When the fishhook-shaped thorn of a multiflora rose bush pricks the skin, the best thing to do is relax, move towards the shrub rather than away, calmly cut the stem to which the thorn is attached, or rotate so the thorn has a chance to slip back out of your clothing.

Learning more about the Asian giant hornet can bring at least a little reassurance. Along with the uncertainty of its establishment in the U.S., I heard via an invasives listserve that "AGH does not attack people unless it feels threatened", and though they do pose a threat to honey bees, they only "attack and kill other bees in the late summer when developing males and future queens need extra protein to complete their life cycle."

The largest wasp in the Princeton area is the cicada killer, which looks much scarier than it actually is. Like dragonflies, they can tackle insects in midair. Ten years ago, there was a colony of cicada killers living near the Princeton Community Pool. Cicada killers are large wasps in Princeton that dive-bomb cicadas in mid-flight, then haul them back to their underground nests to use as food for their young. They pose little danger, but the colony was exterminated by the parks department because the wasps alarmed people walking by in their bathing suits. (Photo is a dramatization featuring our local cicada killer and an unknown actor.)

While pointing out that some threatening looking insects can be benign, I've also long advocated for action on invasive species. As introduced plants like lesser celandine and porcelainberry spread their smothering growth across Princeton's open space and lawns, there is an opportunity to keep them out of some areas through proactive action. It's been very hard to get people to think strategically, however.

The Asian giant hornet is at least being taken seriously. Quick action could prevent it from getting established in the northwestern U.S., though usually an introduced species is already established by the time anyone sees it in the wild.

As with COVID-19, there are questions as to how the hornet would adapt to climate in the U.S. The L.A. Times questioned whether the AGH would adapt to California's cool summers and warm winters.

Some introduced insects become enduring pests, like Asian tiger mosquitoes that bite annoyingly during the daytime, and the Emerald ash borer that has decimated ash trees. On the other hand, we hear little about the killer bees that were touted as such a big threat in the 1980s. The best news would be that the Asian giant hornet hasn't become established after all.

A Pettable Blue-Winged Wasp's Mating Frenzy on Princeton Campus

This post gives a demonstration of wasp petting, and describes a funny thing that happened while helping our younger daughter move into her college dorm.

There's a wasp that's both pretty and pretty harmless. It's named after its wings, which reflect blue in the sunlight, and is easily identified by the rusty orange abdomen with two yellow spots. Scolia dubia, as it's called in latin, is a frequent visitor to the boneset in our backyard garden, more methodical in its nectar drinking than many other wasps.

It's understandable that people are afraid of wasps, given the stings most of us have endured after accidentally stepping on a yellow jacket's nest out in the field. But not all wasps are social like a yellow jacket, or even have nests. A female blue-winged wasp (males cannot sting) has no nest to defend, but rather digs down to lay its egg on an underground grub, then leaves the egg to hatch, consume the conveniently paralyzed grub (usually a larva of the June bug or the Japanese beetle), and emerge on its own as an adult.

Here's an example of how docile these creatures are as they peacefully sip nectar.



This year's visits seemed less frequent than in previous years, leading me to wonder how the species is faring, given all the talk of pollinators being in trouble.

That question was answered in the most unexpected way. Helping our younger daughter move into a dorm for her first year at Princeton University, I noticed one of these blue-winged wasps on a flower near the entryway. Then, on the third or fourth trip in with stuff, I happened to look over at the lawn in the courtyard, and noticed that hundreds of the wasps--let's call it an even thousand--were roaming in zig-zaggy patterns just above the grass. It wasn't at all obvious what they were doing. They looked lost, each flying around and back and forth in its own orbit. Perhaps the grounds crew had blocked their nest, leaving them to search in vain for the entrance. One passerby joked that the wasps were a metaphor for incoming freshmen. Another suggested that the University should take action on what seemed like a threat to the students.

My sense was that any danger was more perceived than real. Having spent many hours this summer photographing the various pollinators visiting the backyard boneset, seeing how harmless are the various bees and wasps when preoccupied with other matters, I waded out into the fray to have a closer look. Were they in fact lost? Or hunting? Or mating? There was no sign of prey, and if they were mating, then why was there so little interaction?

The first clue came only after watching them for awhile. Every now and then, some 20 or 30 of the wasps would suddenly converge on one location in what appeared to be a mad scramble in the grass. It's not easy to photograph wasps zipping around your ankles, but I did manage this photo.

And also this video of one of the sudden convergences. If they were fighting, it appeared brief. If they were mating, it looked pretty clumsy.



Some internet research made it clear that the goal of this mass, planar mingling of wasps was to mate. Some websites state that the males and females do a figure eight-shaped mating dance. Others suggest that those cruising the grass are males waiting for a newly mature female to emerge from the ground. They then converge on the female and compete for a chance to mate. If one's heart can go out to a wasp, my heart went out to the hapless female who, having just emerged as an adult from its underground birthplace, must immediately deal with a frenzied crowd of males seeking to pass along their genes to the next generation. If that is true, though, the sheer numbers and intensity of the gathering suggest that a whole lot of hatching was going on that day, and might the males have also just emerged from the ground? The explanations weren't quite making sense.

I did manage to get up close and personal with one of the convergences, close enough for a voyeuristic view of a male and female taking a tumble amidst the grass blades, clearly mating, with another male up next to them, bending its abdomen and probing in vain. What was surprising was how quickly most males gave up on the project, quickly returning to their holding patterns above the grass.

Here's the online description that best fits what I saw, in a 2016 paper entitled "The Scramble Competition Mating System of Scolia dubia" 

Males of the wasp Scolia dubia search for emerging females by flying low over the ground in areas, such as lawns, that contain the immature scarab beetles upon which the grubs feed. When an adult female emerges and is discovered by a searching male, other males often join the discoverer, forming a frenzied ball of males around the female. When captured along with these males by an observer, a freshly emerged female continues to attract males even after she has mated, presumably because her scent continues to be detected by other males. Some males of S. dubia also search for mates in shrubs and trees encircling a lawn as shown by the sexual response of these males to a frozen but thawed female placed in a shrub or tree known to be visited by flying males. Male flight activity peaks around midday but then diminishes as the afternoon proceeds. 

It was in fact late morning, sunny, warm, and some of the wasps were flying about the branches of the evergreen tree in the middle of the field. But there are many lingering questions. Do these gatherings happen only once per year, or multiple times in the summer? Was this lawn special in some way, or does this happen all over town? And how did these rituals play out before lawn mowers were invented?

One thing is clear. These docile wasps do us a favor by preying on a notorious garden pest--the Japanese beetle. Maybe some September, walking home from the Dinky station, you'll cut through campus and some late-flowering thoroughworts will catch your eye. There, in the clouds of white flowers, blue-winged wasps will be busy living their quiet lives, minding their own business while doing good deeds, their solitary pursuit of nectar giving no clue as to the elaborate choreography that brings them into being.

Attracting Pollinators With Boneset and Thoroughwort

Many people sing the praises of mountain mint and goldenrod for attracting pollinators, but my two favorites are a duo that produce large disks of small white flowers for a long stretch in mid to late summer.

This has been a banner year for boneset and its more numerous but lesser known sidekick, late-flowering thoroughwort.

With a name that spreads like the pagoda-shaped stems that carry its flowers, late-flowering thoroughwort adorns the sides of roads and railroads this time of year. I've seen it cover a whole abandoned field in Montgomery,

and there's a lone specimen blooming at the end of the track at the Dinky station.

It could be called a successful weed, and sometimes it can look a little ragged, perhaps influenced by how much rain comes. But this year it was the most elegant plant in the garden, its loose clusters of flowers like delicate hands reaching out to pollinators.

Late-flowering thoroughwort (left in this photo at the Westminster parking lot raingardens I care for) blooms just as boneset (right) is fading, which this year made for a seamless handoff between the two. Though boneset is comparatively rare in the landscape, it will make seedlings to increase its numbers when planted in a garden.

The two species can easily be told apart by checking the leaves. Boneset has pairs of leaves that are "perfoliate", which is to say they fuse to wrap around the stem. Thus the latin name Eupatorium perfoliatum.

By contrast, the leaves of late-flowering thoroughwort have petioles that extend the leaf away from the stem. The "serotinum" in its latin name, Eupatorium serotinum, means late summer. We could call it the serotinal thoroughwort, but we don't. In the common name, the word "wort" means plant, and if there's anything thorough about a thoroughwort, it's the copious blooms.

Both these wildflower species rise each year to the perfect height for viewing all the varied insect life they attract. Spend some time in that honey-scented space around the flowers and you'll discover an ecosystem in miniature, the flowers being a stage where the protagonists not only feed on nectar, but also look for mates, and sometimes put their lives on the line.

You might think it dangerous to be in proximity to the many kinds of bees and wasps that frequent this floral saloon, but I have never been stung in all my hours immersed in quiet observation.

I've even taken to petting the more docile creatures, like this "solitary" blue-winged wasp. Knowledge can cut through fear. It helps that the more aggressive insects, such as "social" wasps like yellow jackets, spend their summers elsewhere.

If anything, the pollinators are at much greater risk than I, with an occasional preying mantis showing up to snare a fly,

or a brilliantly disguised ambush bug lying in wait for a bumble bee.

Here's the ambush bug that was hiding in that previous photo.

Each plant has a time-release approach to flowering, with some clusters of flowers opening just as others are fading. Week after week in the summer, working in tandem, boneset and late-flowering thoroughwort continue to play host to a shifting cast of insect characters--each with its own traits, backstory and motivations--all the while adding ornament to the garden.