Compost Fly

Ptecticus trivittatus
Ptecticus trivittatus

I captured this fly after dark, at our front porch light in early August, 2013. After capture, the fly spent the night in a vial in our refrigerator. The following morning as soon as there was plenty of light, I released it. Being chilled, it stuck around long enough for a few photographs.

Looking at this fly, and the photographs of the fly, I was immediately struck by it’s colors, the translucent greens and ambers, its size and shape, the venation and rippling look of flowing water in the wings. Only later could I identify it as a Yellow Soldier Fly, Ptecticus trivittatus. This fly, common in eastern North America, is most often observed near compost piles and fermenting fruit, so why was it hanging around the porch light after dark? Those big compound eyes and the pronounced ocelli indicate it’s well adapted to low light conditions; maybe it’s just that the earthy wine these flies seek, decanted from decaying lawn clippings and fallen fruit, is better in the shade. My subsequent encounters with this species placed it at our compost pile, but it also showed up again after dark, at the mothing light on several occasions.

Ptecticus trivittatus
Ptecticus trivittatus

Looking for more information about the fly on the web, I came across a short note in the journal Psyche by Philip Rau, author (along with his wife Nellie) of Wasp Studies Afield (1918). Here are a few passages in summation of our compost fly, in Rau’s characteristic flouncy style, written around 1930, in or near Kirkwood, Missouri:

“…these attractive greenish-colored flies were seen hovering in courtship dance above garbage heaps on the rear of a lot… To say that they dance incessantly is not wholly true for individuals often leave the throng to rest on a tin-can or bottle or cantaloupe skin… indeed, it’s a pretty sight to see a flock of these flies moving in a horizontal plane in more-or-less irregular circles and in figure eights just an inch or two above the mass of multi-colored refuse.”

Ptecticus trivittatus (total length=14mm)
Ptecticus trivittatus (total length=14mm)

Resources

Bugguide page for Ptecticus trivittatus.

Eric R. Eaton. Kaufman Field Guide to Insects of North America. Houghton Mifflin Harcourt. 2007.

Phil Rau. Notes on the Courtship and Mating of the Fly, Ptecticus trivittatus Say. Psyche 44:141-142, 1937.

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Goldenrod Gall Fly


Have you ever wondered what’s inside those hard balls on goldenrod stems?

When I was young, my father had cut them open with his jackknife and used the grubs inside for ice-fishing. And I knew, early on, that they were called galls. But it didn’t dawn on me to wonder what the grubs might turn into or what they were doing there in the first place…until now.

Over the last few years, I began to take an interest in plant galls and have done some research and reading on the subject. The silvery cone galls that form on willows might be my favorites, but the goldenrod galls certainly remain the most conspicuous and most frequently encountered. It seems nearly every stand of Canada goldenrod (Solidago canadensis) one walks through has a few galls, burgeoning among the stems.

These galls are caused by the goldenrod gall fly (Eurosta solidaginis), a well known member of the family Tephritidae, the fruit flies. In fact, so well known are these flies, that a description of their lifecycle is included in my copy of Plant Galls by Margaret Redfern, a British book (part of the Collins New Naturalist series). The female gall fly injects an egg into the developing buds of the goldenrod, using her pointy posterior. The egg hatches and the larva burrows further into the plant and secretes chemicals that cause the plant to grow abnormally around it. The larva feeds on this extra growth throughout the summer, then overwinters safe inside the gall (safe except for the wise chickadees which know how to extract them). At some point, late winter or early spring, the larva pupates and the adult flies emerge soon after, about the time the goldenrod begins to grow late spring. The gall flies mate, after an elaborate courtship dance, and the cycle starts over.

Over the winter, whenever I had the chance, I filled my pockets with intact galls, galls that hadn’t been opened by birds. They’ve been sitting in a heap on my desk for months. This morning, going about some other business in my office, I noticed an odd fly sitting atop one of the vials on the desk. When it moved and betrayed the fact that it was alive, I captured it and placed it in the refrigerator. While it was chilling, I pulled up a small goldenrod plant from the front garden and placed it in container on the table and readied the camera.


This fly, a male, was not a strong flier, even before it was cooled. If it concentrated and focused its energy it could fly about eight inches. The males, according to the literature, walk up and down the goldenrod host, locate a choice spot, lay down some pheromones, and await the arrival of a female. The female gall flies, Redfern reports, use their wings for more than a showy display and have the ability to fly a mile or more in search of suitable host plants.

With more galls sitting on my desk like jack-in-the-boxes ready to spring open at any moment, I’m keeping my fingers crossed for a female gall fly, and doubly crossed (if that’s possible) for one of the wasps that parasitize these flies.

Three-banded Robber Fly (Stichopogon trifasciatus)

I spotted this tiny robber fly on a sandy stretch of trail at River Bend Nature Center in Faribault. A very hot day in June, making my way from the Straight River back to my car, I was on the look out for tiger beetles whenever the trail became sandy, but spotted this great little fly instead. The Three-banded Robber Fly is, according to Stephen Marshall’s magnum opus Flies: The Natural History and Diversity of Diptera (2012), the most common Stichopogon in North America, ranging from Canada into Mexico.

Sand Dunes State Forest

Azure Bluet (Enallagma aspersum)Sherburne National Wildlife Refuge June 30, 2012
Azure Bluet (Enallagma aspersum)
Sherburne National Wildlife Refuge
June 30, 2012

One afternoon this last summer, while the rest of my family went boating and water skiing at my brother-in-law’s cabin on Elk Lake, I had the opportunity to visit a few wildlife refuges south of the lake scattered throughout the Sand Dunes State Forest. The dunes, that give this area its name and make it a rather unique ecosystem, were deposited at the shore of a large glacial lake. Like most dune ecosystems, this area of sandy prairie and oak savannah is extremely fragile and very little of it, if any, remains entirely intact. Still, some big efforts have been made, and are still being made, to set aside and restore large tracts of land. Having never visited any of these refuges before, I was eager to explore them.

Driving south from Elk Lake, I couldn’t help but note some similarities between this landscape and the tall-grass aspen parkland in northwest Minnesota where I had spent some time the previous summer. The possibility of discovering a remnant population of Red-veined Meadowhawks (Sympetrum madidum) suddenly fired my imagination. As I stepped from the car to explore a parcel of restored prairie, just upslope from the St Francis River, a golden-hued meadowhawk flew past me and my pulse raced as I inched toward the small bush where it had landed. For a few moments longer, fancy held the upper hand, while I allowed this dragonfly to be a female Red-veined Meadowhawk, but I finally had to concede to reality, allowing it to be a young female Variegated Meadowhawk—a look alike in some ways, but far less of a surprise, especially given the vast numbers of this species observed during spring migration earlier this year. This particular dragonfly had to be the offspring of that earlier generation of migrants. A little ways off, sharing the top of a small tree with a Halloween Pennant, another migrant made an appearance, a Red Saddlebags (Tramea onusta).

My next stop was the Uncas Dunes Scientific and Natural Area. This SNA was established in 1989, following the rediscovery of the Uncas Skipper (Hesperia uncas) in 1983, a butterfly rarity that had been found in this vicinity two decades earlier, in 1961, but had been, assumedly, extirpated at some point after that. This apparently is the case once more as I can find no record of the butterfly after the late eighties. The last record I was able to locate is an online photograph of a pinned specimen, a female collected on June 29, 1989, at the Elk River Dunes. This specimen along with another from 1967 are held at the McGuire Center for Lepidoptera and Biodiversity, Florida Museum of Natural History, University of Florida, (Gainesville, FL, USA). This segregated population, a possible relic from the post-glacial thermal maximum (ca. 8000-4000 B.P.) when major vegetation zones shifted well east of their present positions, is located many hundreds of miles east of nearest populations in South Dakota. I was visiting at the right time of year—who knows, maybe I’d get lucky…

Not more than twenty or thirty yards into the southeast unit of the SNA, I interrupted a thread-waisted wasp as it was carrying its anesthetized caterpillar back to its burrow. The startled wasp (most likely Ammophila procera given the large size of the wasp and the large size of the prey) abandoned her caterpillar and flew a few feet away where she plopped down on the sand, splayed out flat as if to hide. The caterpillar, larva of the speckled green fruitworm moth (Orthosia hibisci), lay in the middle of the trail alive but unable to move. It was very large, longer and many times heavier than the wasp. I watched for a while, taking a few photographs, but the wasp made no move to reclaim the caterpillar. However, when I returned after my walk, the caterpillar was gone, no doubt sealed carefully underground and dotted with a soon to hatch egg. Howard Ensign Evans summed it up well in Wasp Farm, “I don’t know of anything more exciting than to see a large Ammophila running over the ground with a huge caterpillar slung beneath her and then to follow her to her nest and watch the proceedings.” I had forfeited the most interesting part, being bent on finding butterflies, but still it was exciting just to have encountered this wasp.

The trail, crowded by rebarbative banks of poison ivy, shadowed by overarching oaks, led eventually to the SNA. Along the way I was bothered by horseflies and deerflies; actually more than bothered, I was bullied, badgered, and bitten to the point where looking for dragonflies and butterflies became difficult. The flies tried my nose, my eyes, my mouth, and made consistent contact with my blood at the back of my neck. I flinched at the low-buzz of a super-sized horsefly near my right ear and was pleased to see that it was really a Common Eastern Pondhawk flying off with a captured fly. I was doubly pleased when, further along the trail, several Racket-tailed Emeralds decided to tag along and nibble away at the fringes of the deerfly cloud that had amassed about my head. Another insect I was delighted to see, for similar reasons, was the white-bearded and silver-tipped robber fly, Efferia albibarbis. No doubt this large insect predator was dining on the swarm of tabanids and had a gullet full of dissolved horseflies and deerflies, or at least I hoped so.

As I walked out of the SNA, having seen no skippers, I couldn’t help but associate the shotgun-blasted ladyslipper on the scientific and nature area sign near the entrance with the slower, but more methodical violence done to the native flora and fauna of this place as it was developed and farmed over the last 150 years. And I wondered if anyone would ever spot the Uncas Skipper along this trail again.

I did, eventually, track down a few skipper butterflies. First, at a trail head north of Ann Lake, where a quick search of the parking lot and adjacent road ditches along Highway 4 yielded a few Tawny-edged Skippers (Polites themistocles) nectaring at a clump of alfalfa. Not the Uncas Skippers I’d hoped for, but nonetheless a new species for me. And then, a few miles away, in the Sherburne National Wildlife Refuge, at the canoe access to the St Francis River off Highway 1 about a mile south of Elk Lake, I caught sight of a chocolate-brown Northern Broken-Dash (Wallengrenia egeremet) nectaring on hoary alyssum in the middle of a small expanse of sandy prairie.

In that same expanse of prairie, which the canoe access trail passed through, there were also a lot of dragonflies—Eastern Amberwings, Frosted Whitefaces, Calico Pennants—and a great big surprise of a damselfly—an Azure Bluet (Enallagma aspersum). This was, so far as I knew, only the fourth time this species had been recorded in the state. Strangely the records are widespread: Albert Lea, Duluth, Webster, and now here, near the town of Zimmerman, in central Minnesota. I spent a good amount of time photographing this damsel, a strikingly blue male.

In addition to the time spent contemplating the Azure Bluet, I spent a good deal of time trying to get a good photo of a grass-carrying wasp (Isodontia mexicana) that was nectaring on the prairie flowers. This big wasp was extremely active, rarely staying put or standing still as it rooted around in the radiating white blooms of New Jersey Tea (Ceanothus americanus), pollinating like crazy.

White-bearded Robberfly (Efferia albibarbis) Uncas Dunes SNA, Sherburne County June 30, 2012 male
White-bearded Robberfly (Efferia albibarbis)
Uncas Dunes SNA, Sherburne County
June 30, 2012
male

Golden Dung Fly

Golden Dung Fly Cannon River Wilderness Area March 28, 2012
Golden Dung Fly
Cannon River Wilderness Area
March 28, 2012

When I encountered this fly earlier this year, I was astonished by its color and its lavish and outlandish spines, almost like quills on its back. I also thought it must be a robber fly, because of the way it perched and the way it was hunting smaller flies. Zooming in on the photographs, later, revealed a truly strange and fantastic creature. A little research on the web quickly dispelled any niceties I had imagined, especially as this bug’s truly humble origin was revealed…its larvae ate dung. This was not a robber fly but a Golden Dung Fly (Scathophaga stercoraria). If I had known right off what I was looking at, I may not have stopped to watch it so closely or taken the time to get a photo. As it stands, I learned something about looking without judgment, and the reward of holding to simple, unblinkered wonder. Which is why I’ve chosen it as avatar for this blog.

Golden Dung Fly Cannon River Wilderness Area March 28, 2012
Golden Dung Fly
Cannon River Wilderness Area
March 28, 2012