Archive for Lepidoptera

CAN YOU SAY OSMETERIUM?

Posted in Butterflies, Defense, Education with tags , , , , , , , on September 16, 2010 by Dr. Art Evans

By Arthur V. Evans

This summer a cadre of dedicated parents and volunteers joined forces at a nearby elementary school to create an outdoor classroom. The Holton Learning Project Garden includes a vegetable and butterfly garden that will introduce Holton Elementary School students, their families, and the residents of Belleview and beyond to the pleasures and benefits of urban gardening.

Compared to the dreary, sterile plantings of exotic trees, shrubs, and groundcovers found throughout much of the neighborhood, the vegetable and nascent butterfly garden has rapidly become a local hot spot for insects and spiders. As such, it provides an excellent site for macro photgraphy. Since August, I have endeavored to photograph as many of its multi-legged denizens as possible as part of an ongoing effort to document the arthropod diversity of my neighborhood in Richmond, Virginia.

While walking through the garden yesterday afternoon, I noticed several clumps of green spikes rising sadly from the straw-covered beds. I soon confirmed my initial suspicions as to the identity of the culprits that laid these once fat bunches of parsley to waste. At the very base of one of the clumps were two brightly banded larvae of the black swallowtail, Papilio polyxenes, polishing off the last few leaves.

When I knelt down to photograph the ravenous caterpillars, I accidentally brushed up against their food plant. Both caterpillars reacted immediately by assuming defensive postures. Bent over backwards, they spit up green fluid and produced a pair of long tentacles (osmeterium), that resembled bright orange horns. Soon my nostrils were filled with a strong, disagreeable odor that is best described as “spicy vomit.”

The osmeterium consists of two soft, finger-like tubes that are everted from inside the body through a slit in the prothorax just behind the head as a result of  increased blood pressure. This defensive gland is found in the caterpillars of swallowtail butterflies and is coated with highly noxious chemical compounds (2-methylbutyric acid and isobutyric acid) that deter predators, especially ants.

© 2010, A.V. Evans

A BEVY OF BUCKEYES

Posted in Butterflies, Insects, Virginia with tags , , , , , , on September 15, 2010 by Dr. Art Evans

By Arthur V. Evans

For the past month or so, Virginia has been awash with the Common Buckeye, Junonia coenia. The name Junonia is derived from the diminutive form of the Greek Juno, Zeus’ consort, while the specific epithet, coenia, comes from the Greek kionos meaning common. With six distinct eyespots on their wings, these handsome and energetic insects cannot be confused with any other butterfly species in the Commonwealth.

Their rapid, low, and somewhat erratic flight consists of fluttering strokes occasionally interrupted by meandering glides usually of no more than a foot off the ground. When alarmed, Common Buckeyes are capable of taking to the air in a rapid and sustained flight. They sip nectar from a variety of flowers and frequently rest in open, sunny spots in neighborhoods, parks, wetlands, fields, roadsides, and other open habitats with plenty of low-growing vegetation.

The orange-headed and metallic blue-spined caterpillars are highly variable in color and pattern. They feed on plants in several families and are especially fond of those in the snapdragon (Scrophulariaceae) and acanthus (Acanthaceae) families.

Although they occur throughout the United States, Common Buckeyes only persist in the frost-free southern and eastern halves of the country; individuals observed in the Great Lakes States, New England, and southern Canada are migrants. In eastern United States, these butterflies are in evidence throughout the winter in Florida and the coastal regions of southeastern and Gulf States.

© 2010, A.V. Evans

LUNA MOTHS ARE ON THE WING

Posted in Insects, Moths with tags , , , , , , on April 21, 2010 by Dr. Art Evans

By Arthur V. Evans

The luna moth, Actias luna (Linnaeus). Although the luna moth is native to North America, most of its relatives live in Asia.

Last night, while black lighting for beetles on a cool and still spring night in the Bull Run Mountains in northern Virginia, I was treated to an incredible display of luna moths, Actias luna (Linnaeus). Within an hour of turning on the lights, a baker’s dozen of these marvelously green and ornately tailed creatures had settled on the sheet and nearby tree trunks. Such a sight made me feel quite giddy and brought back a flood of memories of some of my earliest encounters with other spectacular insects as a young naturalist.

The first luna moth that I ever saw in Virginia flew through an unscreened upstairs window. It looked like a soft, green bat as it circled the light at the top of the stairs. It was all that I could do to keep it from being gobbled up by our cats!

They range throughout the hardwood forests of eastern North America. Luna moths were long known to naturalists by the time they were described by Carolus Linnaeus in 1758. The earliest known reference to luna moths in North America was in a note published James Petiver 1700, who had based his comments on a specimen collected in Maryland.

Like other moths and butterflies, the wings of luna moths are covered with scales that make up their colors and patterns.

Luna moths typically emerge from their cocoons in the morning. Powerful fliers, they are often attracted to porch lights and well-lit storefronts. There is only one generation produced in the northern parts of its range and two or three generations are produced in the south. Moths emerging in spring are bright green or blue-green with prominent reddish-purple margins on the outer forewings, while summer broods tend to be more yellow over all with yellowish outer wing margins.

Mating takes place after midnight. Pairs of luna moths sometimes remain coupled until the following evening. Eggs are laid singly or in small batches on upper and lower surfaces of leaves and hatch in about a week. The ravenous and solitary caterpillars feed on the leaves of a wide range of hardwoods, including birch, hickory, walnut, persimmon, and sweetgum. Different populations of luna caterpillars show regional preferences for host plants.

The feathery, or pectinate antennae of the male luna moth are covered with sensory pits that enable to them to detect just a few molecules of the pheromones released by receptive female moths.

Only when they are ready to pupate do the mature caterpillars wander away from the food plant. Cocoons are spun on the ground among the leaf litter at the base of the host tree. Each cocoon consists of a single layer of thin and papery silk that incorporates one or more leaves.

Sightings of the luna moth’s spring brood will still be possible over the next few weeks. Look for them at lights near wooded areas and you just might be treated to a glimpse of one of North America’s most spectacular animal species.

© 2010, A.V. Evans

FALCATE ORANGETIPS

Posted in Butterflies, Environment, Insects, Virginia with tags , , , , , , , on April 5, 2010 by Dr. Art Evans

By Arthur V. Evans

After a few false starts spring has finally arrived here in central Virginia, and not a moment too soon. In hopes of seeing some examples of the early spring insect fauna, I recently set out on a warm, sunny day for the James River Park near the 42nd Street entrance.

The orange and slightly hooked wing-tips were the unmistakable field marks of the male falcate orangetip, Anthocharis midea, the only species of orangetip butterfly found in the eastern United States.

The latest floodwaters from spring rains had only just receded, leaving a thin and dusty film of silt and debris high above the river’s usual channel in the park. Just past the flood residue, small plants had raised their tiny blossoms high to lure the season’s first pollen- and nectar-loving insects.

As I wandered upriver toward the Nickle Bridge, a flash of white with a hint of rich orange crossed my path. It slowly yet deliberately flitted about the freshly emerged sprigs of green that populated the edges of the path before finally settling for just a moment or two on a small flower. The orange and slightly hooked wing-tips were the unmistakable field marks of the male falcate orangetip, Anthocharis midea, the only species of orangetip butterfly found in eastern United States.

The females lack the orange patch, but are otherwise similar in appearance to the males. The wings of both sexes are mostly white; the underside of the hind wing bears a finely marbled yellowish-brown pattern. From tip to tip, their wings span no more than one-and-a-half inches across.

Falcate orangetips are among the first butterflies to emerge from their pupae in spring. Widespread in Virginia, they are found in a variety of habitats, including parks, rocky mountain outcrops, open deciduous and mixed pine-oak woodlands, sandhills, and floodplain forests, especially along stream and river courses.

Females lay their greenish-yellow eggs singly on the flowers of various cresses and other members of the mustard family. The eggs soon turn red and hatch into ravenous larvae that devour mostly seed pods, buds, and flowers, and not leaves. Because of the limited number of reproductive structures on each food plant, larger caterpillars will not hesitate to eat their smaller brethren to reduce competition for meager food resources.

Mature caterpillars are green or blue-green and sprinkled with shiny dark plates bearing short bristles. A yellow stripe runs down the length of the back, while a broad white stripe runs from the head and along each side and meet on its backside. The winter is spent, sometimes two, as a narrow chrysalis that is sharply pointed on both ends.

Don’t hesitate to look for these attractive insects in an open woodland or bottomland forest near you. By early June the falcate orangetips will all be gone, and you will have to wait until the following spring for the next generation to once again make their brief and welcome appearance as heralds of spring.

© 2010, A.V. Evans

THE FOREST CATERPILLAR HUNTER, Calosoma sycophanta, IN VIRGINIA

Posted in Beetles, Environment, Insects with tags , , , , , , , on February 24, 2010 by Dr. Art Evans

By Arthur V. Evans

In July of 2008, while conducting a beetle survey of the Bull Run Mountains Natural Area Preserve in Fauquier and Prince William counties in Virginia, I found numerous metallic green elytra scattered along a foot trail winding through an oak woodland on a west-facing slope. The area had been heavily infested with larvae of the gypsy moth, Lymantria dispar, as evidenced by thousands of larval exuviae and pupal cases that festooned the trunks of oaks and other hardwood trees.

At first glance, I thought the beetle remains were those of the indigenous caterpillar hunter or fiery searcher, Calosoma scrutator, a common, brightly colored, and widespread carabid beetle found in the mountains and lowlands of Virginia. Closer inspection revealed that the elytra were much brighter and more yellow than those of C. scrutator and lacked the characteristic coppery red margins.

Further searching in the area produced a very fragile, yet nearly intact specimen ensnared in an abandoned spider web. The pronotum of this specimen was mostly black with metallic blue along the margins, rather than bluish with violet or coppery yellow green borders typical of C. scrutator. Of the five other species of Calosoma known in Virginia, only C. wilcoxi has entirely metallic green elytra, but it is smaller and much duller than either C. scrutator or the silk-wrapped remains in question. (Figure 1).

Figure 1. The Virginia species of Calosoma (from top to bottom, left to right): C. calidum (F.), C. externum (Say), C. frigidum Kirby, C. sayi Dejean, C. scrutator F., C. sycophanta (L.), and C. wilcoxi LeConte. The scale bar equals 5.0 mm. © 2009, Chris Wirth.

I soon realized that what I had in my possession were the remains of a European species, the forest caterpillar hunter, C. sycophanta. Long known as an important predator of gypsy moth larvae in France, 4,046 of these beetles were imported into the United States between 1905 and 1910, most of which were released in New England to combat outbreaks of two European species of lymantriids: the gypsy moth and the browntail moth, Euproctis chrysorroea.

In the United States, the forest caterpillar hunter is established in Connecticut, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Rhode Island, Vermont, and Washington. They have been released in Delaware, Michigan, Washington, and West Virginia, but they have yet to become established in these states. In spite of releases on Vancouver Island, British Columbia, Quebec, New Brunswick, and Nova Scotia, the forest caterpillar hunter does not appear to be a permanent resident in Canada either.

Both the adults and larvae climb trees to attack and eat caterpillars and pupae of gypsy moths and other species. Adult males are more likely to be found on tree trunks, while females tend to remain on the ground. Based on observations in the laboratory and in the field, both sexes are active day and night. Males tend to be more conspicuous as they spend most of their time actively searching for mates. The more secretive females spend much of their time buried in the soil and hidden among leaf litter to feed and lay eggs.

Adult activity coincides with the larval activity of the gypsy moth. Beetles emerge from their overwintering sites in June to search for prey and mates, although some beetles may remain dormant for up to two years. Although adults are strong and agile fliers capable of leaving their overwintering sites behind to search for high populations of caterpillars, their appearance at new outbreaks of gypsy moths is by no means certain. In fact, beetles released as part of biological control programs often remain near their release site.

Forest caterpillar hunters will attack a variety of other caterpillar species, but are most abundant where populations of gypsy moth caterpillars are high. They remain active for about a month, re-enter the soil, and remain there until the following spring.

Adult predation is not this species’ primary impact on gypsy moth populations. It’s greatest impact is through larval production and the voracious appetites of the beetle’s larvae for mature caterpillars and pupae. The ability of adult beetles to reproduce is directly dependent upon the availability of high densities of gypsy moth caterpillars, especially since females require sufficient protein to ensure successful development of their eggs.

Eggs are laid in the soil beginning in early July and hatch in 4-7 days. The larvae climb trees in search of caterpillars and pupae. The remains of pupae attacked by beetle larvae have characteristically large and jagged holes. Mature beetle larvae seek pupation sites in the soil. The entire life cycle, from egg to adult, takes about seven weeks. In Connecticut, adults are known to live three to four years.

Anecdotal evidence suggests that forest caterpillar hunters are potentially important predators of gypsy moth larvae and pupae, but there is still much to learn. Nearly all of the information on the ecology and behavior of C. sycophanta was gathered during the brief period of adult activity that coincides with gypsy moth outbreaks, but little is known about the ecology of this species between outbreaks.

Many thanks to Chris Wirth for the wonderful color plate. This essay is excerpted from Evans, A.V. 2010. The forest caterpillar hunter, Calosoma sycophanta, an Old World species confirmed as part of the Virginia beetle fauna (Coleoptera: Carabidae). Banisteria [2009] 34: 33-37. The full article is available at http://fwie.fw.vt.edu/VNHS/banisteria/banisteria.asp.

©2010, A.V. EVANS

INSECT CAMOUFLAGE-NOW YOU SEE THEM, NOW YOU DON’T!

Posted in Defense, Insects, Uncategorized with tags , , , , , , on May 26, 2009 by Dr. Art Evans

In nature, survival is the name of the game. Over the millennia, animals have evolved countless ways of avoiding danger, especially to defend themselves against predators. Insects in particular have a stunning array of defenses at their disposal. They run, jump, fly, bite, sting, and pinch. Many have bodies coated with itchy hairs or bristling with sharp, painful spines. Others have bright, conspicuously colored bodies that warn potential predators of their bites, stings, or foul tastes. Some are mimics, sporting the colors and behaviors of pugnacious, bad tasting species, but are in fact harmless themselves. But most insects protect themselves by simply remaining out of sight. And many of them do this with camouflage.

Camouflage, the French word for disguise, first appeared in popular English usage in 1917. To many, the word camouflage brings to mind the color patterns used on military combat uniforms and armaments, patterns that have since been adopted as the “official” garb of many anglers and hunters. But these and other uses of camouflage were all inspired by examples in nature, especially insects.

The simplest type of insect camouflage involves having body colors and patterns that help to conceal their bodies against specific backgrounds in their environment. For example, the leafy green hue of some praying mantids helps them to blend in among shrubs and low growing herbaceous vegetation.  In other species, such as the Carolina mantis, gray individuals are better suited for concealment on tree bark. The cryptic lifestyles of these and other predators help them to mask their presence from both predators and prey.

Toad bugs are small, squat, bug-eyed predators with grasping front legs. They hop along the shores of streams and lakes in search of small insect prey.

Toad bugs are small, squat, bug-eyed predators with grasping front legs. They hop along the shores of streams and lakes in search of small insect prey.

The shores of streams, rivers, and beaches are frequently occupied with ground dwellers whose body colors and textures are perfectly adapted for living concealed lives along the edge. One of my favorite examples is the aptly named toad bug. These small, squat, bug-eyed predators with grasping front legs hop about the wet sands and fine gravels, ever ready to pounce on even smaller insect prey.

Some grasshoppers and caterpillars have the ability to change their colors to match temporary backgrounds. Locusts can adjust their colors to match dry, open ground or lush, green vegetation. Many caterpillars avoid detection by using counter shading and are usually lighter below and darker above.

Papilio001

Not all cryptic species of insects resemble rocks, sticks, or leaves. The early stages of spicebush swallowtail caterpillars have white and black blotches on their body that makes them look like a bird dropping.

The colors and patterns of these and other insects have developed gradually through the process of natural selection. Individuals that avoid detection by predators through camouflage are able to pass along their favorable traits to their offspring generation after generation. Over time, this continual fine-tuning eventually results in colors and patterns that are ideally suited to enhancing their survival in a particular habitat. But effective camouflage isn’t just about matching colors and blending in. It is also about breaking up the outline of an insect’s body so that it looks less like a prey item to a hungry bird or lizard.

Diaphemora002

Stick insects look and behave like a stick. During the day stick insects remain almost motionless, lest they give their position away. But sometimes they will gently rock back and forth, as if they were swaying in a breeze.

Another camouflage tactic is to match the color and look of specific objects in the environment. This form of camouflage is called crypsis, a word derived from the Greek word kryptos, meaning to hide or conceal. Cryptic insects not only have the same colors as sticks, leaves (living or dead), and rocks, but their bodies are also shaped to look like them, too. Hungry predators pay little attention to these and other seemingly inedible objects when they are on the prowl for flesh.

Effective crypsis is more than just looks; it’s also about behavior. Cryptic insects have to select the right background and orientation so that color and form blend seamlessly into the right background. Landing on the wrong place, or settling in the right spot but in the wrong direction will inevitably lead to discovery and death.

geometrid larva001

With its stiff body and gray, bark-like skin, this geometrid moth caterpillar is a dead ringer for a twig.

Once, while walking down a path, I saw a twig-mimicking caterpillar stiffly protruding from the middle of the pavement.  Its gray, warty skin was a dead-ringer for a twig. Had it been on a tree or shrub, I never would have noticed it. But for whatever reasons, it had decided to conspicuously take its defensive pose out in the open on a flat, black background.

Phyllium001

The java leaf insect, cousin of the stick insect, has a flat, leaf-like body covered by a pair of leaf-like wings, all supported by six leaf-like legs.

Some of the most stunning examples of insect crypsis are species found in tropical rainforests. It is not uncommon to see these insects utilize every part of their body to help them look like something else. Java leaf insects, cousins of stick insects, have a flat, leaf-like body covered by a pair of leaf-like wings, all supported by six leaf-like legs.

dead leaf katydid001

This Costa Rican katydid is a dead leaf mimic. Note the markings on the wings suggesting the veins of a leaf.

Of course, no defense strategy is 100% effective. Birds and other sharp-eyed predators can pick up the presence of cryptic insects by their symmetrical shapes. Tropical katydids have gotten around this by having asymmetrical wing shapes and patterns. Each forewing has its own set of spots and notches suggesting leaves that have been randomly attacked by insects and fungus.

Sometimes symmetry is detected by the narrowest of shadows. Many cryptic insects purposely avoid casting shadows by pressing their bodies and appendages tightly against the substrate. Others have fringe lining their bodies and appendages that eliminates shadows altogether.

Every time I go out in search of insects, I am continually fooled by bits of vegetation that appear at first glance to be a cryptic insect. But every now and again I am rewarded for my efforts with yet another surprising example of insect camouflage. This and other revelations are constant reminders that there are lifetimes of insect discoveries to be made.

©2009, A.V. Evans

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