Archive for the Defense Category

COW KILLERS LACK THE VELVET TOUCH

Posted in Ants, bees, wasps, Defense, Insects, Parental care, Predators/parasites/parasitoids with tags , , , , on September 22, 2010 by Dr. Art Evans

By Arthur V. Evans

Velvet ants, some of which are also known as cow killers, are actually solitary wasps. The females are wingless and sting, while the stingless males are fully winged. Although incredibly painful, the sting is seldom dangerous. Velvet ants are rarely abundant enough to need any sort of control and are best left alone to go about their business.

Velvet ant diversity is greater in southwestern United States, less so in the Southeast. Although there are more than 40 species of velvet ants found in the Southeast, only one species in the region, Dasymutilla occidentalis, stands out. It is the largest species of velvet ant in North America and occurs from Connecticut to Florida, west to South Dakota and Texas.

In spite of its nickname “cow killer,” the stings of the female D. occidentalis are not fatal to cattle. The bold and contrasting colors of this velvet ant serves to warn predators that they are quite capable of defending themselves. They also make a squeaking sound by rubbing two abdominal plates across one another as an additional warning. The stingless male is automatically defended by its close resemblance to the female.

Lone females are often seen wandering about on the ground in open habitats from spring through late summer. Winged males patrol these same habitats for mates. Both males and females drink nectar for their nourishment. After mating, females begin searching for the ground nests of bumble bees. Upon finding a nest, the female velvet ant lays a single egg at the entrance of a bumble bee nest. The larva develops inside the nest as an external parasitoid on a bee grub; pupation occurs in the bumble bee’s nest.

Resource: Evans, A.V. 2007. National Wildlife Federation Field Guide to Insects and Spiders of North America. NY: Sterling. 497 pp.

© 2010, A.V. Evans

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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

GRASSHOPPER LOVE

Posted in Arizona, Defense, Grasshoppers & crickets, Insects with tags , , , , , on September 15, 2010 by Dr. Art Evans

By Arthur V. Evans

Arguably the most spectacular looking and certainly among the most distinctive of all the grasshoppers in North America, painted grasshoppers, Dactylotum bicolor (24-32 mm) are a riot of color. These boldly marked orthopterans are also known as rainbow or barber-pole grasshoppers. Studies have shown that diurnal predators, especially birds, will avoid eating them presumably because of their aposematic coloration. Females tend to be significantly larger than the males.

Painted grasshoppers make their living along the western edge of the Great Plains from southern Saskatchewan south to western Texas and northern Mexico, and west to Arizona. Active from mid- to late summer, painted grasshoppers feed on a wide variety of desert plants, especially grasses and low broadleaf plants.

© 2010, A.V. Evans

BEETLES OF EASTERN NORTH AMERICA: GOLDENROD SOLDIER BEETLE

Posted in Beetles, Defense, Insects with tags , , , on September 15, 2010 by Dr. Art Evans

By Arthur V. Evans

The goldenrod soldier beetle, Chauliognathus pennsylvanicus (DeGeer) (9-12 mm).

Late summer and early fall is the time for goldenrod soldier beetles, Chauliognathus pennsylvanicus (DeGeer). Adults feed on pollen from various flowers, especially goldenrod (Solidago), growing in gardens, parks, fields, meadows, and along roadsides and woodland edges.

These conspicuous beetles are often used as research subjects by scientists studying mating behavior, color polymorphism, dispersal, and genetics. This common and widespread species is found over much of eastern North America, ranging from southeastern Canada south to Florida, west to Colorado and Texas.

The margined leatherwing, Chauliognathus marginatus (Fabricius) (7-15 mm).

The head of these conspicuous and aposematically marked beetles is black and the pronotum is wider than long. By contrast, the head of the early spring/early summer margined leatherwing (C. marginatus), has a thick v-shaped mark, while the pronotum is longer than wide. The dark elytral spots of both species are either confined to the posterior half of elytra or extend along their entire length.

Dead and contorted soldier beetles are sometimes found on plants with their mandibles imbedded in stems or leaf edges. These beetles have succumbed to an infection by Eryniopsis lampyridum, a fungal pathogen that also attacks other insects. The open wings of the fungal victims are thought to enhance dispersal of the killer fungus’ spores.

© 2010, A.V. Evans

BELLY UP TO THE GRAVEL BAR FOR TOAD BUGS

Posted in Aquatic, Defense, Insects, Predators/parasites/parasitoids, True bugs, Virginia, Virginia State Parks with tags , , , , on March 28, 2010 by Dr. Art Evans

By Arthur V. Evans

One of my favorite haunts for insect photography is a small and unassuming gravel bar located just downstream from the dam that keeps the Swift Creek Lake within its banks in Pocahontas State Park, Virginia.

The toad bug, Gelastocoris oculatus, is widely distributed throughout southern Canada and most of the United States.

Gravel bars are tough places to live. Their surfaces can reach blistering temperatures or be completely inundated by flooding waters. Still, they support insects adapted to live under such harsh conditions that are seldom found anywhere else.

Many larger species spend their days hiding under stones and their nights foraging for food and mates. Some smaller species spend their entire lives comfortably wedged between the narrow, wet spaces between pebbles and coarse grains of sand. And still others are just passing through.

Not long ago, with a rushing stream at my back, I slowly knelt down on thankfully padded knees to recalibrate my focus on this universe wrought small. It took me of bit of time and patience to get my head out of the hustle and bustle of modern-day life, shake off the city with its noise and congestion, and begin to really see and appreciate the tiny inhabitants of this rocky shoal.

Bit by bit I took in my surroundings. Suddenly, a bit of movement drew my eyes toward a small embankment. I kept staring at the spot as I inched toward it, hoping to see whatever it was moving again. But it didn’t. Then it did, and I zeroed in on the spot. Just as the short, warty bug with bulging eyes came into focus, it jumped away. It was a toad bug, Gelastocoris oculatus.

It was as if I had just seen an old friend. I can still remember my very first encounter with this species along the edges of Little Rock Creek that meandered slowly out of the San Gabriel Mountains to the southern fringes of the Mojave Desert in Southern California. This species of toad bug is widely distributed throughout southern Canada and most of the United States.

The rough bodies of toad bugs are usually dull and mottled with brown and black. The base colors range from almost entirely yellowish, reddish-yellow, grayish-black, to nearly black. As a result, toad bugs are masters of the disappearing act.

Their front legs resemble those of a praying mantis, only shorter and chunkier. And like praying mantises, toad bugs are voracious predators and use these legs to capture small insects.

In Virginia, both larvae and adults live gregariously in a variety of habitats along the muddy, sandy, or gravelly margins of ponds, streams, and rivers. Overwintering adults appear in spring to feed and mate.

From May through September each female lays a dozen or so white eggs at a time in the sand, probably 200 or more in their lifetime. The eggs hatch in about two weeks; another two or three months are required before the larvae reach adulthood.

The toad bug eventually abandoned the gravel bar and disappeared into some low herbaceous growth nearby. I turned to find a small coppery ground beetle with bulging eyes, bright green legs, and patches of purple on its back running across the gravel, but this is a story for another time.

© 2010, A.V. Evans

WINTER DARK FIREFLIES

Posted in Beetles, Defense, Insects, Virginia, Winter with tags , , , , , , , on March 15, 2010 by Dr. Art Evans

By Arthur V. Evans

Today was cool, gray, and blustery–not exactly what I would call ideal conditions for finding insects. Nevertheless, I set out for the woods along Jordans Branch in Bryan Park here in Richmond, Virginia in hopes of finding early spring species to photograph. I ambled down a trail through a stand of holly toward a mixed woodland of loblolly pine and various hardwoods. As I knelt down to inspect the trunk of a pine snag, a faintly beetlish outline partially hidden in a crack in the bark caught my eye.

The winter dark firefly, Ellychnia corrusca, is mostly dull black with yellow, orange, or reddish arched bands along the sides of their midesection.

It was a winter dark firefly, Ellychnia corrusca. Flat and soft-bodied, the beetle measured slightly more than one half inch in length. It remained motionless until I gently coaxed it out of its hiding spot with a pine needle for a better look.

Winter dark fireflies are mostly dull black, but the sides of their flattened, shield-like midsections are marked with yellow, orange, or reddish arched bands. Their soft, pliable wing covers are clothed in short, fine, golden hairs.

Mature larvae pupate in dead logs, especially pines. Adults emerge in late summer and fall and are sometimes encountered on trees or on the flowers of goldenrod and other asters. As temperatures begin to drop, they seek protected places under bark for the winter. The beetles reappear on late winter and early spring days, either resting on bark or circled around sap flows on maples like cattle around a trough.

Like their more familiar cousins of summer, winter black fireflies are bioluminescent, at least for a while. Both the larval and pupal stages produce their own light. Even freshly emerge adults maintain this youthful glow, but as the beetles grow older they lose their light-producing organs.

Mating winter dark fireflies are not an uncommon sight. Their courtship involves two stages. First, the male climbs on the back of the female while constantly touching her with his antennae and mouthparts. This activity alone may last for up to half an hour. Afterward, the couple consummates their relationship by joining their bodies as they face away from one other. Sometime during the next hour or so, the male transfers a protein-packed packet, or spermatophore, to the female. Pairs of beetles sometimes remain joined together this way for up to an entire day. Over the next several days the female will slowly digest the spermatophore inside her body and store it as a source of energy in her body. Both males and females will mate several times before dying in late spring or early summer.

When attacked, these beetles exude a bitter fluid from their leg joints. This defensive strategy, known as reflex bleeding, is also practiced by other species of lightningbugs.In spite of their chemical defenses, phorid flies attack winter dark fireflies and their kin. Just how the flies locate their hosts is unknown, but their maggots develop inside the beetle, killing their beetle host as they emerge to pupate.

Recent studies suggest that winter dark fireflies are not a single species, but represent a complex of closely related, yet undescribed species that inhabit most of eastern North America. The taxonomy and natural history of these handsome, delicate, harbingers of spring would make an excellent study for a student looking to make a significant scientific contribution to the study of North American beetles.

© 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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