Month: August 2020

During a recent conversation with a Master Naturalist over some holes in leaves of ornamental mallows, I shared my inability to find one of the usual suspects associated with shredded mallow leaves, the mallow sawfly, a wasp we met in a previous episode. My rather public response elicited a flurry of rejoinders from gardeners and naturalists whose dogwoods were ravaged this year by another member of the sawfly clan, called the dogwood sawfly. Sawflies are primitive members of the bee and wasp order of insects known as the Hymenoptera. Unlike their kin, who either feast on the flesh of other arthropods or dine on nectar and pollen of plants, several families of sawflies feed on leaves. So this week seems to be a good time to catch up with a couple of fascinating leaf-munching sawflies.

Let’s start with dogwood sawfly. One of the favored hosts of dogwood sawfly is grey dogwood, Cornus resemosa, but silky dogwood, Cornus amomum, and flowering dogwood, Cornus florida, are also on the menu. Winter is spent as a larva ensconced in a chamber built in rotting wood or sometimes structural wood, including siding. In spring larvae pupate and later, from May through July, adults will emerge to fly and find mates. Females deposit eggs on the undersurface of dogwood leaves in clutches numbering 100 or more. Eggs hatch and larvae consume leaf tissue and develop through summer. With the approach of autumn and imminent leaf drop, large sawfly larvae wander from dogwood trees to construct overwintering redoubts in wood. Although many sawfly larvae bear a striking resemblance to caterpillars, the larvae of moths and butterflies, most can be distinguished from Lepidoptera larvae by the number of pairs of appendages called prolegs found on abdominal body segments. In addition to three pairs of jointed walking legs on the thorax, most caterpillars have five or fewer pairs of fleshy prolegs on their abdominal segments. By contrast, in addition to the requisite three pairs of thoracic legs, most sawflies bear six or more pairs of prolegs.

Snaky dogwood sawfly larvae practice their curls beneath a leaf while an almost fully developed larva waves to the camera while searching for another meal.

As larvae, dogwood sawflies have, quite literally, a colorful juvenile history. After hatching from eggs, larvae are rather translucent yellowish creatures resembling gummy worms. As they develop and molt, specialized glands produce a snowy-white cloak of wax. Fully developed larvae shed the white waxy cloak and assume a dashing color scheme of yellow, white, and black. Why the chameleon routine? Well, some scientists have speculated that the brilliant white coloration and elongated body of young larvae may mimic a bird dropping and reduce the chance of predation. What self-respecting bird eats bird droppings, right? Another hypothesis suggests predators and small parasitic wasps may be unable or unwilling to effectively attack sawfly larvae through their cloak of wax.

Last week while on an adventure along the Patuxent River, I spied what I believed was a larva feeding on a patch of dastardly stilt grass. Delighted that something might be eating this aggressive invader, I investigated the critter and was disappointed to find nothing but an empty exoskeleton adorned with tufts of fluffy wax. Above the stilt grass towered a lovely black walnut tree whose leaves were disappearing down the gullets of another sawfly known as the butternut woollyworm.  Unlike its cousin the dogwood sawfly, this sawfly spends winter as a pupa in the soil enclosed in a durable case. In spring adults emerge and, after mating, females use their saw-like egg-laying appendage called an ovipositor to insert eggs into the mid-vein of walnut leaves. Newly hatched larvae are naked but soon develop a flocculent cloak of magnificent white wax. Upon molting from one instar to the next, this cloak is shed but often remains attached to a leaf for several days or falls on underlying vegetation like stilt grass to fool passing entomologists. In addition to black walnut, Juglans nigra, as their common name implies woollyworms also frequent butternut, Juglans cinerea, and have been reported from hickories, Carya spp. Over the next week or two, be on the lookout for these waxy sawflies on dogwoods and trees in the walnut family. Try to imagine what all the wax is about.  

High in the canopy, butternut woollyworms dine on leaves of a black walnut tree. Although their white waxy mane evokes visages of a shaggy dog or Cousin Itt, the flocculent cloak may dissuade attack by predators or parasitoids. White, waxy filaments dancing in the breeze may not advertise a tasty meal to vertebrate predators accustomed to naked caterpillars for dinner.

 Acknowledgements

This episode is dedicated to our friend Jimmy and in memory of Angela who shared their sawflies and inspired this Bug of the Week. The interesting articles “Be Alert for Dogwood Sawfly” by Joe Boggs, Insects that Feed on Trees and shrubs by Warren Johnson and Howard Lyon, and “Seasonal Cycle and Habits of the Butternut Woollyworm” by L.L. Hyche were consulted in preparation of this episode.

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In a previous episode of Bug of the Week, we lamented the scarcity of swallowtail butterflies in our gardens. Swallowtails have been scarce, but in my flower beds, bumble bees have been rocking. Bumble bees build nests in the ground, often in the former burrows of chipmunks, or sometimes in the hollow of a fallen tree. One might think a carefully constructed subterranean nest defended by bumble bees would be a pretty safe place to raise young. Most of the time this is true, but not so when red velvet ants are in town. This gorgeous insect is not an ant at all. Ants are social insects ruled by one or more queens governing a caste system of workers. Velvet ants are wasps in the family Mutillidae, a large group of solitary wasps that prey upon ground-nesting bees. We met a fast-moving velvet ant in the caldera of a sleeping Costa Rican volcano in a previous episode of Bug of the Week. The female velvet ant featured this week was discovered dashing about a local landscape. Red velvet ants are reported in most counties in Maryland and in addition to my home in Columbia, I have received images or specimens from Adamstown, Pasadena, Queenstown, and Bowie.  

Velvet ants, including the one we meet today, are part of a large mimicry ring. Bright contrasting colors of dozens of species of velvet ants, including Dasymutilla occidentalis, send a warning to potential predators that an attack will be met with a potent retaliatory response, a wicked sting. The easily recognized shared appearance of so many species of velvet ants is called Müllerian mimicry, first proposed by famed German naturalist Fritz Müller. Although lacking wings, the velvet ant is no slow poke. She runs like a demon while searching for a nest of unsuspecting bumble bees. Her powerful jaws and terrible stinger probably allow her to fight her way past bumble bee defenders and enter the brood chamber of the bee hive. In the brood chamber, bumble bee larvae are nourished and cared for by bee workers. The velvet ant lays a single egg on or near the bumble bee’s babes. This egg hatches into a velvet ant larva that consumes a developing bee. When fully developed, the wasp larva forms a pupa and later emerges as an adult velvet ant. Although female velvet ants are wingless, male velvet ants have wings that are shiny and jet black. The males fly about in search of flower nectar, pollen, and mates.  

It’s been a good year for bumble bees in my garden, working the blossoms and returning to nests, often abandoned chipmunk burrows. Elsewhere in the lawn, female red velvet ants prowl, searching for nests of ground nesting bees and wasps. If you see this amazing creature, avoid the urge to pick it up unless you yearn for a very memorable sting.

The lovely female velvet ant in this episode has yet another defense in addition to jaws and stinger. When grasped, she emitted a clearly audible squeaking sound. Squeaking, or stridulation in bug lingo, is a vibration produced by an insect. In this case stridulation occurs on the abdomen where one body part rubs against another. What purpose does the squeaking serve? Along with the bright red and black coloration, the loud squeak probably serves as a warning to any would-be predator that this beauty packs a punch. You see, the other common name for the red velvet ant is “cow killer.” When I grabbed one with a pair of forceps, an enormous, angry stinger emerged from the tip of her abdomen in search of something to punish. Some say that the sting of a velvet ant is strong enough to kill a cow. While this surely never happened, people stung by the velvet ant report a highly painful experience, long to be remembered.   

 Acknowledgements      

 We thank Tracy for the inspiration for this episode and for sharing an image of a beautiful eastern red velvet ant. Dr. Shrewsbury risked an awesome sting while capturing the subject for this episode. The fascinating article “North American velvet ants form one of the world’s largest known Müllerian mimicry complexes” by Joseph S. Wilson, Joshua P. Jahner, Matthew L. Forister, Erica S. Sheehan, Kevin A. Williams, and James P. Pitts, and the buzzy “Bees, wasps, and ants” by Eric Grissell were used to prepare this episode.

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Community gardens are fertile hunting grounds for interesting insects. On a recent visit to the West Side Community Garden in Columbia, Maryland, patches of milkweeds, mountain mints, and monardas were humming with pollinators large and small. In addition to the standard bees, butterflies, and flies, a couple of very impressive black wasps were busy in the florets. These were not social wasps like Asian giant hornets, European hornets, bald faced hornets, and yellow jackets, all colonial wasps that live in a nest ruled by a queen. These were solitary wasps, a part of the digger wasp clan. The larger of the two, Sphex pensylvanicus, goes by the name of great black wasp, while its smaller orange-legged cousin, Sphex nudus, is known as the katydid wasp.

As members of the digger clan, female great black wasps and katydid wasps excavate galleries a foot or more deep in the soil. This crypt will serve as the nursery and larder for the developing wasp larvae.  Female Sphex wasps search the treetops for those beautiful and melodious nighttime troubadours, the katydids we met last week. Once she locates her prey, she stings and transports her prize back to the subterranean burrow. Inside the burrow she provisions each brood cell with two to six victims and lays an egg on the underside of one katydid. Here is where this macabre tale gives me the willies. The katydids in the crypt are not really dead. They are just mostly dead, like the tortured Dread Pirate Roberts in the movie Princess Bride. Ah, but there will be no Miracle Max to rescue these unfortunate creatures. The venom of the great black wasp does not kill its prey; it merely paralyzes the victim. The moribund katydids are alive but cannot escape the jaws of the wasp larva as it proceeds to consume the hapless prey one by one over the span of about ten days. Whew, makes me glad I am not a katydid. Fully developed larvae spin cocoons in autumn and remain underground through winter, awaiting the return of summer before emerging from the earth to sip nectar and hunt katydids, crickets, and grasshoppers.

Sphex wasps are very fond of mountain mint and spotted horse mint. When the wasp probes the blossom for nectar, anthers dip down and release their pollen on its back.

One of the most curious pollination events takes place as great black wasps nectar at spotted beebalm, a.k.a horsemint (Monarda punctata), one of my favorite flowering plants by virtue of the vast number of insects it attracts. Unlike open-faced flowers such as sun flowers, horsemint provides a curious array of petals, anthers, and stigmas. Nectar fiends like the great black wasp land on petals and, as they probe deeper into the flower, pollen laden anthers dip down and discharge their yellow pollen grains onto the back of the wasp. As the insect moves from floret to floret pollen accumulates, turning the back of the great black wasp yellow. The transformation of the great black wasp to the great yellow-backed wasp never fails to amuse me. Spotted horse mint will always have a place in my garden.

Acknowledgements

The fascinating article, “The life-history and habits of the digger-wasp Ammobia pennsylvanica (Linn.)” by John A. Frisch was used as a reference for this episode. Bug of the Week thanks Dr. Shrewsbury for providing the inspiration and image for this story.

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Last week a friend inquired about all of the racket created by unseen insects as scorching days melted into somewhat less scorching nights here in the DMV. Near sunset as we enter the twilight zone, shrill daytime calls of several species of annual, a.k.a dog-day, cicadas are replaced by the courtship serenades of hopeful dusk-calling male cicadas and male katydids. Specific frequencies, amplitudes, and tonal patterns are used not only for species recognition, but also by females of each species to decide who will be the father of their nymphs. The winners of the entomological version of ‘The Voice’ win the right to mate and thereby move on to the finals evolutionarily, so to speak. Cicadas produce sound by vibrating a membranous, drumhead-like organ on the sides of their abdomen called a tymbal. The enlarged and mostly hollow abdomen of the cicada acts as an amplification chamber producing vibrations of 100 decibels, one of the loudest sounds in the animal world.

Watch as an annual cicada scales a tree before taking flight to the canopy. The abdomen of a daytime-singing cicada vibrates as he woos his mate. Leaf-mimicking angle-wing katydids are common in our area. Grooming appears to be an important part of the daily routine. To hear the gentle call of the greater angle-wing katydid, please click on this link. http://songsofinsects.com/katydids/greater-anglewing

Katydids use a very different anatomical mechanism to create sound. The katydid’s remarkable musical anatomy includes a forewing with a series of teeth called the file and an opposing forewing with a scraper. When the file moves across the scraper, vibrations reverberate across the wing – the song of the katydid. The common true katydid, Pterophylla camellifolia, creates an amplification chamber by bowing its forewings to help resonate its call. The result is one of the loudest and most easily recognized of all katydid songs.

So, if the guys are singing their hearts out, female cicadas and katydids must be able to hear their songs, right? Right! Both male and female cicadas have membranes called tympana on their abdomen that enable them to detect vibrations. The auditory organs or “ears” of katydids are located inside chambers of the front of their forelegs. How strange. As the dreadfully hot summer day transitions to evening, listen for the calls of the dusk singing cicada and enjoy his attempts to woo a mate in the treetops. And as twilight transitions to dark, when the songs of cicadas’ end, soon will begin the chorus of the katydids, serenades of six-legged summer romances.

Acknowledgements

“Songs of Insects” by Lang Elliott and Wil Hershberger, the wonderful Songs of Insects website, and “The mechanics of sound production in Panacanthus pallicornis (Orthoptera: Tettigoniidae: Conocephalinae): the stridulatory motor patterns” by Fernando Montealegre-Z and Andrew C. Mason were used as references for this episode. Special thanks to Jen Franciotti for providing the inspiration for this episode.  

To hear the song of one of our local dusk singing cicadas, the Northern Dusk-singing Cicada, Megatibicen auletes, please click on the following link: http://songsofinsects.com/cicadas/northern-dusk-singing-cicada

To hear the song of one of our local nighttime chorusing katydids, the Common True Katydid, Pterophylla camellifolia, please click on the following link: http://songsofinsects.com/katydids/common-true-katydid

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 “Where are the butterflies?” Somewhat panicked questions like this started arriving several weeks ago and they don’t seem to want to go away. At first I was reluctant to acknowledge another concern in a year rife with uncertainty surrounding murder hornets, COVID19, and social unrest. Last week after a miserable showing of swallowtails at my butterfly magnet, also known as cup plant (Silphium perfoliatum), I shared the butterfly worries with several distinguished colleagues who confirmed that, yes, some butterflies were indeed scarcer this year in their gardens too. What a contrast to the summer of 2019, which seemed like butterfly nirvana with more than two dozen swallowtails nectaring at the same time on the cup plant in the front flower bed. This year, the butterfly magnet attained a paltry 3 swallowtails at any moment during the same week in which almost three dozen were sighted last year.

So, what gives with the butterfly drought? We know that changes in land use patterns associated with urbanization are responsible for dramatic losses in several insect species, including butterflies, in cities around the world. However, declines in the abundance of butterflies from one year to the next are often linked to more immediate ecological events. There are several key drivers of insect abundance. One important determinant of insect abundance is weather. In previous episodes we met a pair of invaders from the south, harlequin bugs and kudzu bugs. We have learned that as winter temperatures dip into the low teens and single digits it is simply too cold for these rascals to survive in Maryland, and their populations persist only in warmer redoubts further south. A second vital factor for insect survival is, of course, food. Changes in insect populations related to food resources are generally termed bottom-up effects. Part of the explanation for declines in monarch populations in North America are linked to reductions in populations of milkweed plants critical for larval survival. Moreover, scarcity of high quality nectar sources necessary to sustain adults as they migrate to overwintering hideaways, survive winter’s chill, and sally forth in late winter and early spring to colonize breeding grounds may be reducing populations.  A third major factor affecting insect populations, known as top-down effects, stems from Mother Nature’s hit squad of predators, parasites, and pathogens attacking, consuming, or infecting their victims. Long-term suppression of gypsy moths resulted when scientists reunited a fungal pathogen, Entomophaga maimaiga, from Asia with this killer of oak trees. This widespread pathogen helps keep gypsy moth at bay throughout much of its range.

How does all this relate to missing butterflies? Most notably scarce are several of large swallowtail butterflies including eastern tigers, black swallowtails, and spice bush swallowtails we visited in previous episodes. Butterfly experts suggest that some of these large swallowtails may have been fooled by some exceptionally warm weather in February followed by a rainy, chilly, and in some places frosty March, April, and May. Freeze warnings, frost, and record cold temperatures were recorded in several locations in Maryland in early May. Perhaps a few late season frosts took a toll on these beauties. On the bottom-up side of things, some think that drought stress in late summer and early autumn of 2019 may have reduced the quality of food resources for caterpillars as they completed development, thereby reducing their numbers or perhaps reducing chances for survival of pupa about to face winter’s wrath. Some have suggested that a really good year last year for some caterpillars translated into higher numbers of parasitoids and predators. In previous episodes we met rapacious caterpillar killers like wheel bugs and spined soldier bugs. We also know that many vertebrate predators, including insectivorous birds such as chickadees, depend on caterpillars for their survival. When numbers of caterpillars increase, so too do the numbers of these birds. While swallowtails have been scarce this year, I have never enjoyed as many blue jays, cardinals, wrens, and chickadees zooming around the yard as I have this spring and summer. Perhaps a bounty of caterpillars in the spring of 2019 translated into greater numbers of predators and parasitoids that put a damper on populations of some of our butterflies this year.

Swallowtails and some other butterflies seem unusually scarce in the DMV this spring and early summer. Unusual weather including late spring frosts, poor quality food resources last autumn, and mortality related to predators and parasites may have conspired to reduce their numbers.

Should we fear that a scarcity of swallowtails in 2020 portends a pending butterfly apocalypse? Nah, I don’t think so. Many other species of butterflies appear to be doing just fine. Silver spotted skippers and their kin arrived in my garden right on schedule in great numbers, as did cabbage butterflies. Peregrinations along the C & O Canal this spring and summer revealed zebra butterflies in good numbers and doing just fine. However, scientists warn that in the long term issues such as urbanization and climate change, including bizarre and severe weather patterns, spell trouble for many species of plants and animals, including insects. But as I finish writing this episode and look out the window to the cup plant, I see four tiger swallowtails getting their carbohydrate fix. Maybe upcoming broods of swallowtails will be bigger and better than their predecessors.

Acknowledgements

Bug of the Week thanks science writer, butterfly guru, and keeper of the Lep Log Rick Borchelt  for his insights and observations of butterflies throughout the region. Many thanks to colleagues in the Department of Entomology, especially Karin Burghardt and Leo Shapiro for providing references and helping clarify several points discussed in this episode. The following fascinating papers were consulted: “Western Monarch Population Plummets: Status, Probable Causes, and Recommended Conservation Actions” by Emma M. Pelton, Cheryl B. Schultz, Sarina J. Jepsen, Scott Hoffman Black and Elizabeth E. Crone; “Multiscale seasonal factors drive the size of winter monarch colonies” by Sarah P. Saunders, Leslie Ries, Naresh Neupane, M. Isabel Ramírez, Eligio García-Serrano, Eduardo Rendón-Salinas, and Elise F. Zipkina; “Declines and Resilience of Communities of Leaf Chewing Insects on Missouri Oaks Following Spring Frost and Summer Drought” by Robert J. Marquis, John T. Lill, Rebecca E. Forkner, Josiane Le Corff, John M. Landosky and James B. Whitfield; and “Nonnative plants reduce population growth of an insectivorous bird” by Desirée L. Narango, Douglas W. Tallamy, and Peter P. Marra.

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