CAN YOU SAY OSMETERIUM?

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

SKY ISLANDS, DESERT SEA-Part II, Hornworm Highway

By Arthur V. Evans

Charged by the onset of the summer monsoons in July or August, the arthropods of Arizona’s Sky Islands and desert seas are stirred into action.  The sudden and intense infusion of life-giving moisture triggers a flush of activity: eggs hatch, hungry larvae gobble up new leaves, adults are released from their earthen or wooden chambers, eager to mate and reproduce.  It is this marvelous intensity of arthropod activity that has drawn me to the mountains, desert scrub and grasslands of southeastern Arizona for nearly 40 years.

My earliest impressions of Arizona’s desert seas were formed by numerous overland trips from California in the 1970’s. Within minutes of crossing the Colorado River, the first saguaros would greet us, stationed like lone sentinels high on the rocky ridges of the Dome Rock Mountains. Although these giant columnar cacti have become symbolic of all arid regions of the southwest, they are strictly indigenous to the Sonoran Desert. These and other nearby desert ranges are capable only of supporting plants and animals adapted to fleeting amounts of rain. The summer monsoons, even at their height, seldom penetrate this far north and west.

Driving east from Gila Bend to the Maricopa Mountains, the stands of saguaros become taller and denser. Compared to the deeply pleated trunks of their western brethren, the almost bulging flesh of these plants is a clear sign of increased precipitation. The saguaros’ spongy inner tissues rapidly expand to absorb and store seasonal supplies of water as a hedge against the inevitable drought ahead.  Even the spiny ocotillo stand taller and greener here, surrounded by dense thickets of palo verde.  Here all living things enjoy the increased benefits of living under the blanket of the summer monsoons.

Another sure sign of increased rainfall is the sporadic population explosion of green and black-striped hornworms, caterpillars of the white-lined sphinx moth, Hyles lineata. Dozens to hundreds of these insects race across the hot, blistering highway in a scramble for tender desert greens. Some years there are so many of the caterpillars that the pavement becomes slick with their crushed bodies. At night marauding three-inch-long shield-backed katydids of the genus Capnobates rip chunks of sun-dried caterpillar from the road and grind them up with their powerful jaws, while scores of ants carve up the leftovers and carry them back to their underground brood.

© 2010, A.V. Evans

LUNA MOTHS ARE ON THE WING

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

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 42^nd 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

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

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.

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.

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.

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.

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.

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.

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