When pearly-eye meets dragonfly: Northern pearly-eye, Enodia anthedon, and clubtail dragonflies, Gomphidae spp.

 

Gorgeous Cobra Clubtails often rest with wings widespread on trees near their riverine hunting grounds.

 

The sleepy rivers and streams flowing in the Cacapon watershed in West Virginia’s panhandle are home to a rich bounty of plants and animals. Along creeks, ponds, and moist forest edges, blades of white cutgrass and bottle brush grass provide nutrition for caterpillars of the pretty pearly-eye butterfly. Adult pearly-eyes cruise verdant forest glens in search of sap-fluxes on trees and deposits of animal dung, from which they harvest proteins and carbohydrates used to develop eggs and to provide energy to search for just the right vegetation on which to deposit eggs. But for pearly-eyes, danger lurks along the creek banks and pond edges in the form of fearsome aerial hunters, clubtail dragonflies.

While living the life aquatic, fierce dragonfly nymphs consume untold numbers of mosquito larvae.

Dragonflies belong to an ancient order of insects called the Odonata that evolved some 300 million years ago. Both adult and juvenile Odonata are predators. Dragonfly nymphs live the life aquatic, prowling slow moving creek beds and ponds searching for aquatic invertebrates like mosquito larvae, and even small vertebrates like tadpoles and small fish. In a previous episode, we saw the lightning fast strike of dragonfly nymphs as they captured and ate unsuspecting mosquito wigglers. Dragonfly nymphs have been touted as providing significant reductions in mosquito populations around the world. Adult Odonata are familiar to most of us and go by the common names of dragonflies and damselflies. More than 6,000 species of dragonflies and damselflies have been described.

Dragonflies are masters of the aerial hunt and capture their victims while on the wing. Legs festooned with stout spines are held basketlike beneath the dragonfly as it zooms through the air. Prey such as moths, butterflies, bees and sometimes other Odonata are captured in the basket. Does eating your near relative somehow seem so wrong? One large and particularly aggressive clubtail dragonfly, Hagenius brevistylus, is nicknamed the dragonhunter due to its Hannibal Lecter-like propensity to eat other dragonflies and damselflies. Dragonflies often consume their prey while in flight. When not in flight, meals are enjoyed on vegetation or stones, as is the case with the clubtail we meet in this episode.

Northern pearly-eye butterflies are common denizens of riparian forests in the eastern United States. They rest on vegetation and tree trunks. But when in flight, they are hunted by fierce aerial predators, clubtail dragonflies. Watch as a clubtail chows down on a hapless pearly-eye butterfly. Clubtails show no kinship loyalty when it comes to dining. This one is happy to feast on an unlucky damselfly.

Dragonfly nymphs exit their aquatic nursery, climb vegetation, and shed juvenile skins to become aerial hunters in the world above the water.

Many species of dragonflies reside year-round in the DMV and spend the winter underwater as juveniles. Others, like the common green darner, migrate to southern realms in autumn to avoid winter’s chill and return north the following year. In fact, dragonflies are contenders for the world record of longest insect migration. Pantala flavescens, the “winged wanderer”, is thought to cross oceans and continents with migratory flights of more than 10,000 miles in search of exactly the right pool of water in which to deposit eggs. In the waning days of summer, enjoy these magnificent predators that roamed our skies millions of years before the first dinosaurs walked the earth.

Acknowledgements

“Dragonflies as an Important Aquatic Predator Insect and Their Potential for Control of Vectors of Different Diseases” by Hassan Vatandoost, “Tiny dragonfly shatters insect migration record-Insect traverses oceans and continents” by Virginia Morell, and “Beginners guide to dragonflies” by Blair Nikula, Jackie Sones, and Donald and Lillian Stokes were consulted to prepare this episode.

Devilish times for hickory: Hickory horned devils and royal walnut moths, Citheronia regalis

 

Adorned with horns and almost six inches in length, the hickory horned devil caterpillar is harmless unless you are a hickory tree. Image credit: Bill Miller

 

The ginormous pupal case of the royal walnut moth is the largest one I’ve ever seen.

Hickory trees are one of my favorites by virtue of their delicious edible nuts and spectacular fall color, which is just around the corner. Ah, but I’m not the only one with a fondness for hickory and this week Bug of the Week had the chance to visit one of the coolest members of the Lepidoptera clan who also love hickory, not for its nuts or fall color but for its nutritious leaves. Let’s see one of the most fantastic members of the silk moth family, a huge beautiful caterpillar called the hickory horned devil. Last week a lucky gardener shared an image of an enormous caterpillar resting on vegetation in his landscape. How lucky was he to find a hickory horned devil? Real lucky, as my one and only personal encounter with this beauty happened a few years ago when bug-centric neighbors delivered to me a rather large, dark, cigar-shaped object they discovered in the duff beneath a walnut tree. Not many insects in Maryland form a pupa that can fill a hand, but this one did. The lucky pupa took up residence on my kitchen counter for a month or so until one morning a vacant pupal case was replaced by a very impressive moth clinging to the sofa in the family room.

From her royal chamber, the female royal walnut moth released a pheromone to attract a mate. It worked and in the morning a male had joined her in the cage.

The royal walnut moth, a.k.a. regal moth, has but one generation in Maryland each year. Life is short for giant silk moths such as this. Unlike its relatives, butterflies or hawk moths, silk moths lack functional mouthparts and do not eat as adults. They live only a few days. Their sole mission is to find a mate, mate, and lay eggs in a suitable place before being discovered and eaten by a bird or other hungry predator. To attract a mate, a female moth releases a volatile attractant called a sex pheromone. Usually, this takes place on an upright structure such as the trunk of a tree on the night following emergence from the pupal case. Not wishing to stand in the way of true love, but concerned that this magnificent princess would be eaten by a bird, my royal walnut moth was confined, Rapunzel-style, in a predator-proof bridal chamber, which was in this case a squirrel-proof bird feeder. On the evening of her resplendent debut, she was placed outside to court her mate. Her pheromones were strong and apparently irresistible. In her chamber the following morning was a male royal walnut moth.

‘Tis the season when hickory horned devil caterpillars will be seen strolling on patios as they search for places to pupate. Their story began weeks ago when male and female royal walnut moths hooked up and the female deposited eggs on leaves of hickory and other members of the walnut family. Eggs hatched into bizarre tiny caterpillars with very stout spines. They grew into gorgeous green giants before moving to the soil to form a pupal case to pass the wicked winter. Next spring beautiful royal walnut moths will emerge from these pupal cases. Video credits: Diane Pedicini, M. J. Raupp

Female (above) and male (below) royal walnut moths make a regal couple indeed.

Shortly after the royal couple completed their connubial interlude, the female left her chamber and began to deposit eggs on almost every surface she encountered. While taking a momentary rest on my leg, she treated me to eight large eggs just above the ankle. The eggs of the royal walnut moth are typically laid on leaves of a tree suitable to meet the nutritional needs of the developing larvae. Eggs hatch in about a week and the larvae develop into one of the most striking caterpillars on the planet, the hickory horned devil. This giant of the silk moth world may attain a size of five to six inches when fully grown.

Leaves of walnut and hickory are favored sites for royal walnut moths to lay eggs.

Favored hosts for larval development are plants in the family Juglandaceae such as walnut, butternut, and hickory. Hickory horned devils have also been recorded eating ash, beech, lilac, persimmon, sumac, and sweet gum. Fortunately, the male performed his task admirably, and after a few weeks dozens of small devils hatched from the eggs. The task of feeding this many hungry mouths soon exceeded the time budget of this bug geek and after a couple of weeks and a few quick molts, the caterpillars were emancipated to several walnut and hickory trees on the College Park Campus of the University of Maryland. Perhaps the wisdom and beauty of a creature that has transcended epochs of change on our planet can impart some of the same to this year’s incoming class of freshman. Let’s hope so.

Acknowledgements

Bug of the week thanks Bill Miller for providing the image of a hickory horned devil that served as the inspiration for this episode. Many thanks to Diane Pedicini for the cool video of a hickory horned devil crawling across her patio, and to Jeff and Linda for providing a giant pupa for this episode. David Wagner’s incomparable ‘Caterpillars of Eastern North America’ was used as a reference.

Tiny toads and even tinier toad bugs: Big-eyed toad bug, Gelastocoris oculatus

 

Toad bugs really do live up to their namesake in both appearance and hopping ability.

 

Many common names of insects tell us something about their appearance and traits. For example, lace bugs surely have delicate lacey wings and stink bugs certainly live up to their name with their odor. This week along the pebble strewn banks of Catoctin Creek, a bucolic tributary of the mighty Potomac River, we visited small jumpy toads and even smaller jumpy toad bugs. Toad bugs are somewhat obscure and often overlooked members of a large clan of insects known as Hemiptera. Here in North America we have more than 10,000 species of Hemiptera, but less than 10 species of toad bugs. We met many other hemipterans in previous episodes including heroic predators like wheel bugs and two-spotted stink bugs, and other hemipterans which are sometimes meals for these heroes like the felonious brown marmorated stink bug.

Like all predatory hemipterans, toad bugs have sucking mouthparts used to pierce the exoskeletons of their prey and a tiny pump in their head used to imbibe the liquid contents of their victims. Both immature stages called nymphs and adults cruise over the mud and sand and sneak about pebbles and vegetation lining the creek bank in search of small insects and other arthropods to eat. They hunt like cats - stalking prey, pouncing on them, and subduing them with highly specialized front legs. These raptorial legs are designed with spines to help snare their prey, much like the spines on the forelegs of praying mantises.

A warm late summer afternoon is a hopping good time to visit wildlife on the rocky banks of creeks and rivers. In addition to small jumpy toads, much smaller predators called toad bugs hunt tiny invertebrates along the pebble strewn shore. Watch as a toad bug lives up to its name and makes a jet-propelled escape from the camera lens. Even when slowed by 95% the takeoff is too fast to see. A super-close look confirms their toad-like appearance.

Their unusual body shape and muddy, mottled coloration help them blend in well with the creek bank, thereby avoiding the searching eyes of their own predators. When the subterfuge of camouflage fails, they skitter across the mud and make impressively long jumps to avoid capture by their enemies or bug geeks. At less than a centimeter in length they easily jump more than ten times their body length, shattering Mike Powell’s world record which, by the way, is only about five times his body length. With lots of warm late summer days left before autumn’s chill, head to a creek and cool off. And while you’re wading on the shore, don’t be surprised to see some Fowler’s toads and their hemipteran lookalikes, toad bugs, hopping between the pebbles.

Acknowledgements

Bug of the Week thanks Ellie, Abby, and Cassidy for helping to spot and catch toads and toad bugs that were the inspiration for this episode. We thank the fine naturalists at Catoctin Creek Nature Center for providing a wonderful refuge for nature amidst a rapidly developing landscape. “An Introduction to the Study of Insects” by D. J. Borer, D. M. DeLong and C. A. Triplehorn was used as a reference for this episode.