Archive for the Predators/parasites/parasitoids Category

A MIGHTY MITE!

Posted in Arachnids, Predators/parasites/parasitoids with tags , , , on September 23, 2010 by Dr. Art Evans

By Arthur V. Evans

In the deserts of Africa, Asia, Europe, and North America large velvety red mites appear suddenly after heavy rains. Southwestern United States has at least two species of these amazing mites.

This past July, I came across a lone individual of a giant red velvet mite, Dinothrombium magnificum (LeConte) emerging from its burrow just east of the Patagonia Mountains in southeastern Arizona where it inhabits the Sonoran Desert and adjacent uplands.

Giant red velvet mites are spectacular for several reasons. First, the largest individuals measure in at a whopping one centimeter in length, which makes them the largest mites in the world. They are covered with a thick coat of scarlet hair-like setae. The mite’s bright red color is apparently aposematic in function and serves to warn predators of their bad taste. Entomophagous animals offered giant red velvet mites either rejected the arachnids outright or quickly spit them out.

Although often difficult to find, they are sometimes extremely abundant locally, if only for a few hours at time. For example, after a brief yet intense thunderstorm, a massive emergence of giant red velvet mites was sighted from the air at an altitude of 1500 feet just north of  Tucson. An estimated 3-5 million mites had emerged in an area roughly two acres in size!

The annual emergence of the giant mites is apparently timed to coincide with that of their primary prey, termites. However, their opportunity to gorge themselves on abundant termite reproductives is quite limited. After mating, the termites quickly shed their wings and bury themselves so that they are out of reach of the mite’s predatory embrace. Adult giant red velvet mites spend most of their lives in subterranean burrows in a diapause-like state waiting for a specific set of ecological conditions triggered by summer monsoons.

Resources:

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

Lighton, J.R.B. and F.D. Duncan. 1995. Standard and exercise metabolism and the dynamics of gas exchange in the giant red velvet mite, Dinothrombium magnificum. Journal of Insect Physiology 41(10): 877-884.

Newell, I.M. and L. Tevis, Jr. 1960. Angelothrombium pandorae n.g., n. sp. (Acari, Trombidiidae), and notes on the biology of the giant red velvet mites. Annals of the Entomological Society of America 53: 293-304.

Tevis, L., Jr. and I.M. Newell. 1962. Studies on the biology and seasonal cycle of the giant red velvet mite, Dinothrombium pandorae (Acari, Trombidiidae). Ecology 43(3): 497-505.

Zhang, Z.-Q. 1998. Biology and ecology of trombidiid mites (Acari, Trombidioidea). Experimental and Applied Acarology 22: 139-155.


© 2010, A.V. Evans

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

SHARPSHOOTERS AND BROCHOSOMES

Posted in Leafhoppers, Parental care, Predators/parasites/parasitoids with tags , , , on September 17, 2010 by Dr. Art Evans

By Arthur V. Evans

Broad-headed sharpshooter, Oncometopia orbona.

Sharpshooters (Oncometopia species) measure 11-13 mm in length and are among the largest of North America’s leafhoppers. They feed on a wide variety of plants growing in gardens, parks, meadows, and woodland edges during summer and fall. Their sap feeding activities may spread plant pathogens. Females use their knifelike ovipositors to insert eggs into soft stems. The eggs are covered with a chalky substance (egg brochosomes) that make them more resistant to excess moisture and protect them from fungal infections and possibly attacks by parasitoids.

Broad-headed sharpshooter with brochosomes.

Brochosomes are intricately shaped proteinaceous particles that are produced by kidney-like structures called Malpighian tubules and excreted as a solution. After the sharpshooter molts, the solution is spread over the exoskeleton as a water-proof coating. Female sharpshooters store brochosomes as a single white dot on each forewing to be used later as a protective coating for their eggs.

© 2010, A.V. Evans

TARANTULA VS. TARANTULA HAWK

Posted in Ants, bees, wasps, Arachnids, Arizona, Insects, Parental care, Predators/parasites/parasitoids with tags , , , on September 15, 2010 by Dr. Art Evans

By Arthur V. Evans

One of nature’s classic battles is that of the lopsided struggle between a tarantula and its arch nemesis, the tarantula hawk (PepsisHemipepsis). I say lopsided because the odds are usually stacked against the tarantula. The arachnid, paralyzed by the wasp’s sting, is destined to be dragged off and stuffed down a previously dug burrow to become an egg-laying site and eventual fodder for a ravenous wasp grub.

In August, I photographed a tarantula hawk as it dragged a paralyzed female desert blonde tarantula, Aphonopelma chalcodes, across a coarsely gravelled driveway at the foot of the Huachuca Mountains in Sierra Vista, Arizona.

I first became aware of this saga in Walt Disney’s Academy Award winning documentary The Living Desert (1953 and later re-released in 1971) that depicted a day in the life of desert flora and fauna and the struggles of the latter to simultaneously find food and avoid being eaten themselves. It was 10 minutes of film footage featuring a tarantula hawk grappling with a tarantula shot by N. Paul Kenworthy, then a doctoral student at UCLA, that inspired Disney to produce his first documentary. Kenworthy later became one of the two macro cinematographers on the project. I met The Living Desert’s other macro cinematographer, entomologist Bob Crandall, while I was in high school. But that is another story for another time.

© 2010, A.V. Evans

A TALE OF PREDATOR AND PREY

Posted in Ants, bees, wasps, Arachnids, Predators/parasites/parasitoids, Spiders with tags , , , , on May 4, 2010 by Dr. Art Evans

By Arthur V. Evans

I had just spent a grueling three hours in the sweltering afternoon heat stalking insects and spiders with my camera along the James River. As I walked through the gate toward the parking lot at Reedy Creek, I saw a spider wasp with shiny dark wings flitting about agitatedly in the road. With another dozen or so exposures left in my camera, I decided to get a few pictures of the wasp before calling it a day. She flew all around me, landing briefly here and there before taking wing again. My patience quickly wore thin in the heat and I decided that enough was enough. But then I saw what had kept the wasp in the vicinity.

Lying perfectly still and in pristine condition was a wolf spider splayed out in the middle of the road. It had been laid low by the paralyzing sting of the spider wasp and was destined to be hauled off and stuffed down a nearby burrow to become fodder for a wasp larva. I decided to stake out the living corpse right then and there in the middle of the road. Sprawled out in the rapidly fading sun I aimed my camera at its still body in anticipation of photographing the predator with its prey.

For nearly ten minutes the wasp flew circles around me, frequently landing and running over the ground to search in vain for the hapless arachnid. At first I thought she was intimidated by my presence, but several times the wasp came within inches of me and my camera. Time seemed to drag on as the wasp inspected every piece of real estate in the immediate vicinity, except the tiny parcel that actually had the spider.

The occasional cyclist or jogger went past, but no one stopped to ask what I was doing. Then I heard the slow crunching of gravel coming toward me along the railroad tracks. A Richmond police car slowly wheeled toward me and stopped about 50 feet away. From my perspective down on the ground the car’s headlights seemed to stare at me like two giant bug eyes separated by shiny and toothed mandibles.

I smiled in the direction of the officer and wondered what he must be thinking. Just then a big panel truck hauling a trailer load of bright blue kayaks pulled up beside me. I looked up as the driver inquired if I was all right. I assured her that I was just fine and that I was waiting to take a picture of a wasp attacking a spider. She said she hated spiders and hoped the spider would meet its demise and then drove off to deliver her cargo by the river.

Then the police car pulled up. The officer told me that he did not want to ruin my shot and had decided to wait. But then he figured that if the kayak truck hadn’t spoiled my shot, his police cruiser probably wouldn’t either.

With all the hubbub I thought for sure that the wasp would have been scared off, but it was still scouring the ground in search of the spider. Finally it ran right up to the spider and inspected it nervously with its curled antennae. Suddenly it grabbed the spider’s leg with its mandibles and began to drag it away with surprising speed across the open ground.

Just as the wasp and spider cleared the roadway a thundering herd of about 40 young kayakers and their river guides stampeded over the site where I has just spent the past three-quarters of an hour on wasp watch. I paid them little attention as I crouched and crabbed along the access road paralleling the railroad tracks, following the wasp’s progress through my lens.

Every now and again the wasp would abandon the spider, apparently wandering off to reconnoiter the next leg of its journey. After a few minutes I could see the wasp negotiating its way back through the tangled growth.  As before, the wasp briefly inspected the spider with its antennae before grabbing a leg with its mouth and setting off on a new course.

The sunlight was beginning to fade when the spider wasp ditched her booty once again. I had two more shots left and decided to wait for the wasp to return one more time. I waited another 10 minutes or so for the wasp to come back, but it never did. I decided to call it a day and could only assume that the wasp was out somewhere, simultaneously excavating a spider’s grave and preparing a wasp’s nursery.

Excerpt from “What’s Bugging You? A Fond Look at the Animals We Love to Hate, University of Virginia Press. © 2008, A.V. Evans

SKY ISLANDS, DESERT SEA-Part II, Hornworm Highway

Posted in Arizona, Insects, Moths, Musings, Predators/parasites/parasitoids with tags , , , , on April 26, 2010 by Dr. Art Evans

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

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

MANTIDFLIES GET A LEG UP ON SPIDERS

Posted in Insects, Predators/parasites/parasitoids, Virginia with tags , , , , , on March 17, 2010 by Dr. Art Evans

By Arthur V. Evans

A few years back, on a warm muggy evening in September at the Savage Neck Natural Area Preserve on the Eastern Shore of Virginia, I was checking a light trap designed specifically to lure night-flying insects. As the beam of my headlamp swept over nearby shrubbery, my eye caught a pale green insect just over half an inch long perched on a leaf.

The green mantidfly, Zeugomantispa minuta, looks like a cross between a green lacewing and a praying mantid. They live throughout much of eastern United States and are found in a variety of habitats from late June through early October.

With four clear wings folded rooflike over its body and a pair of grabbing forelegs held tightly against its long, slender thorax, this animal looked like a cross between a green lacewing and a praying mantid. In fact, it was the green mantidfly, Zeugomantispa minuta.

Mantidflies belong to the order Neuroptera and are only distantly related to mantids. Instead, they are related to antlions (whose larvae are known as doodlebugs), lacewings, and owlflies. Praying mantids are in the order Mantodea and are actually cousins of cockroaches.

Adult mantidflies capture and eat all kinds of small insects in captivity, but little is known of their food preferences in the wild. The larvae are also predators. Some are known to attack the pupae of moths, or the larvae of beetles, flies, bees, and wasps, while others prey on the eggs of spiders.

There are two basic strategies for mantidfly larvae to successfully dine on spider eggs; they are either egg sac penetrators or spider-boarders. Egg sac penetrators, such as those of green mantidflies, seek out their food directly.

When they find an egg sac they chew their way through the silk casing with highly modified jaws. The grooved mandibles and maxillae fit snugly together to form a pair of piercing/sucking tubes through which they draw out the embryonic fluids of the eggs.

Spider boarders are unable to chew their way inside spider egg sacs. Instead, they seek out a female spider, climb onto her body, and wait. What are they waiting for? Egg-laying day. The larvae disembark just in time to be wrapped up with the eggs in the egg sac.

Those mantidlfy larvae that initially hitched their fortunes to a male must eventually switch to the egg-producing sex. They switch hosts either while the male is mating or being cannibalized by a female.

The life cycle of mantidflies is a type of complete metamorphosis known as hypermetamorphosis. The first larval stage is quite active and resembles a slender, leggy silverfish, a body type that serves them well as they seek out egg sacs or spiders. Once inside the egg sac, the larva switch into feeding mode and go through two  grublike stages before completing their development into adulthood. These fat, short-legged larvae are decidedly more sedentary. Afterall, they are thorax deep in food and have no need to go anywhere.

One of the most amazing things to me about mantidfly natural history is that scientists figured it out at all. The seemingly unlikely relationship between mantidflies and spiders was first described in 1869 and, with careful and patient study, continues to unfold today. It is this unrelenting promise of discovery that keeps me and my colleagues forever enamored with the world of insects and spiders and dreaming of an endless summer.

© 2010, A.V. Evans

%d bloggers like this: