Syrphid Flies

Hover fly, courtesy of the Cornell U. Cooperative Extension

Summertime’s full in the fields and woods of Nelson County, Virginia.  Here in the lee of the Blue Ridge the chickory flowers blue in the day and the datura fills the evening air with the scent of heady nectar.  Tomatoes are ripe, cucumbers fit to burst.  The wild persimmons and pawpaws are loaded down with a fall harvest to give us all bellyaches from too much sweet fruit.  It’s been an abundant year in every respect.

I was out in the garden the other day, attempting to get some weeding done, and harvest the bolting cilantro while I was at it.  In my better moments, I like to take a moment to sit with the plants I’m about to obliterate in the name of gardening or cookery.  Every weed in the yarden probably has a better handle on the local ecology than I dot.  Several times I’ve been about to yank out some presumably offensive uninvited annual when my better self stops me, says, “wait a moment and pay attention,” and some unexpected observation convinces me to just let the dang thing be for a while.  The goldenrod and fleabane I allowed to grow fed a generation of butterflies and beautiful, jewel-colored bees, and the amaranth ended up drawing all the deer to it the time they bucked the fence, leaving my collards and potatoes unmolested.  There’s a wisdom in the weeds, if you take the time to meet them at their level.

Anyway, I went out to pull a bunch of these tangled, anonymous vegetables so my kale could get a little more light.  As I bent down to shear off a clump of fragrantly blooming cilantro, something fast and bright caught my eye.  A flying insect, about the size of my thumbnail, was hovering intensely above a cilantro umbel.  I’d seen these little bugs, striped black and yellow like imitation bees and with a face that seems to be all eyeball, zipping around flower gardens all over, but I’d rarely paid them much mind.  I knew that they were popularly called hover flies, due to their uncanny ability to perfectly maintain their position between ground and sky, and were properly called syrphid flies, from a mistaken appropriation from the Greek (surphos: gnat) some time in the murky primordial days of taxonomic biology, but that was about it.

Fascinated, I sat down, garden tasks momentarily forgotten, and observed this little creature.  He or possibly she made an even circuit of ten or so flowers at the same height on the blooming stem.  At one point a larger hover fly of a different species blundered into the territory.  A flurry of agitated buzzing and aerial acrobatics followed, which left the larger animal fleeing to a higher elevation.  Each hover fly seemed to maintain a vigorously defended set of territories on the cilantro plants in the patch.  I wondered if the territories remained the same throughout the day, or if different ages, sexes, or species took over at different hours.  (I returned a little before dusk to find the hoverflies entirely absent and a whole new cast of moths enacting similar political negotiations.)  The adults were clearly nectar feeders, but what did the young eat?  Hover flies are proper flies (order Diptera) so that means maggots.  Did they lay their eggs in rotting meat like houseflies, or in the soil like the brightly colored stilt-legged flies?  Why were they colored so like bees if they behaved so unlike them?  At rest, a hover fly looks a little like a stinging wasp or bee, but their flight is so distinctive it’s difficult to confuse them.  All the more so for sight-hunting predators like robber flies, crab spiders, and the aptly named flycatcher birds.  How many generations did it take for the presumably drab ur-hover-fly to develop the distinctive livery of a stinging insect?  Which came first, the hover fly or the wasp?  Prehistory was staring me in the face, speaking loudly in an unintelligible gibberish.

My tight focus on the world of a single flower stalk wavered and shifted.  Movement on an elderberry leaf several feet away caught my attention.  A katydid, massive to my eye, stretched its leg as it munched its way along.  Bumblebees meandered between compound clover flowers in the lawn.  Ants followed one another along chemical trails through the jungle of grass and plantain.  A whole universe of little lives opened up across the yard.  One flower stalk to one yard to one forest to one valley to one watershed to one mountain range to one continent to one planet- the hugeness of the scale and the fineness of the detail is too much for my mammalian brain to fully comprehend.

Anyway, I couldn’t very well pull that cilantro- too many other lives depended upon it for me to justify extracting it for the sole purpose of experimental chutney.

Some further notes on syrphid flies:

While the adults are primarily nectar feeders, the maggots of some 110 of known hover fly species are voracious predators.  Eggs are laid at the base of plants frequented by aphids, that tiny, parthenogenetic pest creature, honeydew cow for the ants, and famous food of the ladybug larva.  Upon hatching, the maggots squidge up the stalk, feeling their way to their prey via unknown means (the maggots are totally blind and lacking much of the sensory apparatus of the adult fly).  If you find yourself wrestling with aphids in the garden, and ladybugs and lacewings don’t seem to be doing enough, consider planting more compound flowers around the borders of your garden to attract hover flies.

Other syrphids, the large hairy drone flies, lay their eggs in soupy corpse-muck and other offal.  Their maggots are equipped with a four-inch(!) long ‘snorkel’ which allows them to breathe while fully submerged.


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