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Predator-Prey

Predator Eating Predator

fishing spider and dragonfly 385The Six-spotted Fishing Spider, Dolomedes triton, is an arachnid in the nursery web spider family Pisauridae. As its name implies, the Six-spotted Fishing Spider does occasionally eat small fish, but also consumes other invertebrates and tadpoles. The hunting techniques of fishing spiders are varied. Often they sit patiently during the day, waiting hours with their legs stretched out for an unsuspecting insect (such as the pictured Dot-tailed Whiteface dragonfly) to land on the same lily pad or leaf that the spider is sitting on. They can and do walk on water as well as dive up to seven inches deep in order to catch aquatic prey. The Six-spotted Fishing Spider in this photograph has removed the head of its prey and is drinking its liquefied innards.

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Eastern Newts Dining on Wood Frog Eggs

4-28-15 newts2 329Wood Frogs mate and lay their eggs in ponds and occasionally vernal pools before heading back to their terrestrial, wooded habitat. Amphibian eggs are subject to predation by numerous predators, including leeches, fish, aquatic insects and salamanders. Eastern Newts (aquatic as larvae and adults) are carnivorous and consume insect larvae, fingernail clams, leeches and amphibian eggs, among other things. At this time of year, Wood Frog eggs are plentiful and easily accessible, as the individual masses, each consisting of 1,000 to 2,000 eggs, are deposited adjacent to each other on submerged vegetation. Hungry newts can feed for hours without moving more than an inch, and many often do. After discovering an egg mass, a newt plunges its head into the clump of eggs, grabs one and, with great shaking of its head, separates an egg from the mass and quickly swallows it. Seconds later the newt repeats this process, and continues doing so until it is satiated.

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Red Foxes Locating Prey

OLYMPUS DIGITAL CAMERADeep snow certainly presents challenges to predators – their prey is well hidden for the most part, and if they are to survive, they must compensate for not being able to see what they are hunting. Foxes are an example of how a predator survives in a winter like the Northeast has had. A red fox hunting for food is constantly listening for the sound of rodent feet under the snow, and when it hears them (they can hear a mouse or vole three feet beneath the surface of the snow) they leap up into the air and pounce on or near their prey with their front feet. Most of the time they are not successful, and come up empty-mouthed, but they usually succeed often enough to survive. Biologists are still working on understanding exactly how they do this.

Researchers in Czechoslovakia, watching foxes hunt in the wild, determined that a fox’s success seems to correlate with the direction in which it jumps. If the observed foxes jumped to the northeast they killed on 73 % of their attacks. If they reversed direction and jumped exactly the opposite way, they killed 60 % of the time. But in all other directions — east, south, west, or variations thereof— they were successful only 18% of the time. Jaroslav Cerveny, the Czech researcher, feels that foxes have a “magnetic sense,” and are capable of lining up the rodent sounds that reach their ears with the slope of the Earth’s magnetic field, and when this occurs, dinner is usually caught. (This theory has yet to be confirmed, but the likelihood that it is correct is great.) (Photo by Susan Holland, in the wilds of northwest Ontario)

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Patient (and Hungry) Barred Owls Visit Feeders

3-12-15 barred owl 152Barred owls are nothing if not resourceful when it comes to methods for finding food. Typically they sit on a high branch and scan the area for prey before dropping down to capture small mammals such as mice, squirrels as well as reptiles and amphibians. During summer months, they have been seen perched over water and swooping down to capture fish, as well as wading in shallow water to hunt for crayfish and fish. Barred owls have even been seen running along the ground and pouncing on amphibians.

Even with a myriad of hunting techniques, however, barred owls have had a hard time this winter, due to the depth of the snow (harder to hear and reach prey) and the time it is taking for it to melt. Small mammals, which compose the bulk of their diet, remain well hidden. Reports of barred owls perched patiently waiting and watching on or near bird feeders for unsuspecting rodents to expose themselves have become commonplace. Mice and voles that come out from under the snow to feed on spilled seed during the night are a life-saving source of food for these stressed birds. Warmer weather will hopefully soon improve hunting conditions for barred owls. Their gain will be our loss, for once again, as it should be, a sighting will become a far more rare occurrence. (Thanks to Emily and Joe Silver for photo op.)

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Mystery Photo

Can you read this story in the snow? Hint: it took place at night on the coast of Maine. All guesses can be made under “comments” on Naturally Curious blog page. (Photo by Sally Grassi)

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Northern Short-tailed Shrews

2-4-15  northern short-tailed shrew 025Northern short-tailed shrews, with their short legs, minute eyes and concealed ears, can be found throughout eastern and central U.S. Their eyesight is so poor that all they can do is to detect light, but they compensate by using echolocation for navigation and to locate earthworms, slugs, snails and other invertebrates which comprise their diet. The northern short-tailed shrew and the European water shrew are the only mammals that produce a toxic secretion in their salivary glands. This poison is powerful enough to kill small mammals, but is mainly used to immobilize smaller prey. In winter, although active, the short-tailed shrew limits its activity in order to conserve energy, and relies partially on food that it stored in its burrow in the fall.

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Antlions Trapping Insects

8-14-14  antlions - 230The larvae of a predaceous group of winged insects (family Myrmeleontidae) that closely resemble dragonflies and damselflies are referred to as “antlions” – they have the ferociousness of a lion and prey mainly on ants. The manner in which an antlion traps its prey is ingenious. It excavates a conical pit in sandy soil (an antlion is also called a “doodlebug” because of the squiggly trails it leaves in the sand looking for just the right spot for a pit). Using its head as a shovel, it tosses out sand as it turns in a circle, digging deeper and deeper, until it forms a pit roughly two inches deep and three inches wide. The antlion lies at the bottom of the pit, covered by a thin layer of sand except for it pincer-like mandibles, which are ready to snatch prey at a second’s notice.

The slope of the sides of the pit is at the angle of repose – as steep as it can be without giving way – so when an ant accidentally steps over the edge of the pit and falls in, the sand beneath it collapses, carrying the ant to the bottom of the pit and into the pincers of the waiting antlion. If the ant tries to scramble up and out of the pit, the antlion tosses a load of sand at the ant, knocking it back down. The antlion then injects venom and digestive fluids into the prey via grooves in its mandibles, and drinks the innards of the ant through these same grooves.

The antlion’s anatomy is as unusual as its method of capturing prey. It has a mouth cavity, but no mouth opening, and no external opening for solid waste. Because digestion takes place outside of its body, the antlion doesn’t accumulate a lot of waste, but what it does accumulate stays inside of it until the antlion matures into an adult. This can be anywhere from one to three years, depending on the species. When fully developed, the antlion constructs a small, round pupal case out of silk and sand, in which it overwinters. It emerges from this case the following spring as a winged adult. (Thanks to Joan Waltermire and John Douglas for photo op.)

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Great Golden Digger Wasps Digging Nests & Provisioning Them with Food

8-11-15 great golden d.w.2 159The Great Golden Digger Wasp, Sphex ichneumoneus, is a solitary, predatory wasp whose hunting and nesting techniques are programmed and never vary. Having overwintered underground in a nest dug by its mother, the adult wasp emerges, often in August, and begins preparations for the next generation. She digs several nests in packed, sandy soil, using her mandibles to cut the earth. Emerging backwards from the ground with a lump of soil between her forelegs and head, she flips the soil with her forelegs beneath her body, scattering it to the sides with her hind legs. In this manner she excavates several cells off a central 4-6-inch deep tunnel.

The wasp seeks out prey — often a grasshopper, cicada or cricket – and then stings and paralyzes it. If the prey is small, she flies it directly to the nest. If prey is too large to transport aerially, the wasp will walk with it across the ground, dragging it by its antennae (see photo). She then drops the prey several inches from the nest hole. After crawling down into the nest for a brief inspection, she pulls the prey down into one of the cells while walking backwards. She then leaves to find another insect. When a cell contains paralyzed prey, the wasp lays an egg on the insect. The egg hatches within two or three days and the wasp larva begins eating the insect. Because the prey is not dead, decomposition is delayed, and the wasp larva’s food is relatively fresh. The developing wasps overwinter in the nest and emerge the following summer to begin the process all over again.

If you live near a sunny area of compacted clay and sand that has flower nectar for adults to feed on and crickets, grasshoppers and katydids for their larvae, you may well have a chance to observe this unique ritual. (Thanks to Marian Cawley for photo op.)

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Twelve-spotted Tiger Beetle Larva at Work

7-24-14 tiger beetle adult and larva 040Without doubt, I have one of the most erudite readerships in the land of blogs. Several people recognized this uncommon phenomenon. To clear up a few misconceptions, however, being a male, this dragonfly was not laying eggs. Neither was it fertilizing them – male dragonflies perform this act when coupled with a female. This Chalk-fronted Corporal had the misfortune to sun itself on a tiger beetle-inhabited patch of sand. One of the most aggressive groups of insect predators is the tiger beetle family. They are especially known for their speed – up to 5.6 mph, which is comparable to a human running 480 mph. If you watch an adult tiger beetle hunting, you’ll notice that it stops and starts frequently. This is because it runs so fast it goes blind — its brain has trouble processing the information it sees, and the beetle must stop to regain its sight.

The larvae of the Twelve-spotted Tiger Beetle live in tunnels that they dig in the sand (some of you noticed tiny holes near the dragonfly) that can be up to a foot deep. The larvae have hooks located on the back of their abdomen to anchor them to the side of the burrow. Tiger beetle larvae are also predators, and after digging a tunnel the Twelve-spotted Tiger Beetle will crawl up it until just the top of its head is visible. From this position the larva watches for prey wandering by. When it sees a potential meal, such as yesterday’s dragonfly, it flips backwards faster than you can blink an eye and grabs its prey, pulling it down as far as it can into its tunnel, where it safely feasts on its catch. The portion of the Chalk-fronted Corporal’s abdomen that was inside the tiger beetle tunnel was completely consumed except for the outer skeleton.

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Dragonfly Eclosure: A Vulnerable Time

newt eating dragonfly2 021Dragonfly larvae reside in ponds until the time comes for them to climb up stalks of emergent vegetation or adjacent rocks, split their larval skin and emerge as adults (a process called eclosure). Before it can take flight, a dragonfly has to cling to the substrate long enough to expand its wings by pumping fluid into them, and dry its exoskeleton as well as its wings. During this time the dragonfly is extremely vulnerable – not only can it not fly, but it is usually situated directly above the water. The slightest breeze can blow it from its precarious perch into the water below, where opportunistic predators such as this Eastern Newt are at the ready and make quick work of their helpless prey.

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Barred Owl Story in the Snow

2-17-14  barred owl prints 013These beautiful impressions in the snow tell the story of a Barred Owl diving feet first after prey, most likely a vole or mouse. The fact that there are no rodent tracks on the surface of the snow tells you that the mouse or vole was well hidden in its tunnel under the snow at the time. Apparently the owl’s talons did not reach their target (at least, no blood or rodent remnants), and the owl continued to plow through the snow in repeated attempts to capture its prey before taking flight.

The presence of facial discs (feathers in the shape of a funnel around each eye that direct sound waves towards the owl’s ear) plus the differing size and asymmetrical placement of an owl’s ear openings allow the owl to discern the direction a sound is coming from, how far away it is and its height relative to the owl – even in the dark or under the snow! The exceptional hearing ability of owls, particularly those in the genus Strix (which includes Barred and Great Gray Owls), enables them to plunge into the snow and often successfully capture prey, sight unseen. (Species of owl was determined by wing length. Thanks to Rob Anderegg and Jennifer Grant for photo op.)

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Hide & Seek: Voles & Foxes

1-9-14  hide and seek-fox & vole IMG_2735Unlike wolves, which hunt in packs and often take down prey larger than themselves, red foxes are solitary hunters and as a result often catch prey much smaller than themselves, such as mice and voles. During the winter, mice and voles become more active during daylight hours because much of their time is spent under the snow, where they remain hidden from view. Consequently, in winter you’re more likely to see a fox hunting during the day than in the summer. Whenever it’s hunting, night or day, a fox depends heavily on its acute sense of hearing. It is most sensitive to lower noises such as the rustling and gnawing sounds that small animals make as they move through vegetation or feed on seeds, buds and twigs. Foxes can locate these sounds several feet away, to within inches of their true location, under three feet of snow. Recent research suggests that they may also use the magnetic field to help them locate prey. (photo: red fox & meadow vole tracks)

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The Butcher Bird

1-3-14 impaled mouse & MS shrike by Bridie McGreavy DSC_0146The Northern Shrike (Lanius excubitor) is highly unusual in that it is a predatory songbird. Birds, mammals and insects are preferred over nectar, nuts and seeds. This tundra-nesting bird comes as far south as New England to overwinter, where it preys mainly on mice, voles and small birds. The Northern Shrike often kills more prey than it can immediately eat or feed its young, storing the excess food to eat later, when available living prey may be scarce. The manner in which it stores this extra food is what gave it the name “butcher bird;” it often impales prey on a thorn, broken branch (as in photograph) or even barbed wire, or it wedges prey into narrow V-shaped forks of branches, where they hang until reclaimed by the shrike. (Impaled mouse photo by Bridie McGreavy; northern shrike photo by MS Henszey)

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Northern Hawk Owl

n. hawk owl3- 231The Northern Hawk Owl is a bird of the remote Alaskan and Canadian boreal forests. Its name reflects the fact that this diurnal owl has both the appearance and behavior of a hawk, specifically, an accipiter. Although the Northern Hawk Owl winters throughout its breeding range, it periodically erupts southward into southern Canada and the northern United States. Sightings of this bird are rare in Vermont, but in recent winters, including the current one, there have been some. As with Snowy Owls, the magnitude and extent of these winter irruptions are thought to correlate with high reproductive success followed by severe winter conditions and decreased prey availability, but much remains to be understood about their winter dispersal habits. What we do know is that the Northern Hawk Owl’s skills as a hunter are very impressive. It can detect prey (small rodents, grouse, hares) by sight at a distance of half a mile and just using its ears can find prey under a foot of snow.

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Weasel Tracks

12-24-13 weasel & stonewall IMG_9602When looking for signs of weasel– Long-tailed or Ermine (formerly called Short-tailed Weasel) – in winter, stonewalls are a good place to head. Both of these nocturnal mustelids prey on small rodents such as mice and voles, which frequent the nooks and crannies of stonewalls. In winter weasels cover a lot of ground looking for prey – the home range of an Ermine is between 30 and 40 square acres, but when food is scarce, they may travel two or three miles in one night. Often their tracks will run the length of a stonewall on one side and then back the other side. Intermittent pauses are made as the Ermine stands on its hind feet and stretches its neck out, searching the landscape for both movement and sound.

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Interpreting a Kill Site

12-18-13 hawk kill IMG_4136When there’s snow on the ground and you come upon a site where a predator successfully caught prey, there are usually signs that will help you determine who the main players were. In the above scene, remnants of red squirrel fur confirm the identity of the prey. If you look at the top of the image, you can make out a faint wing impression. Although not in this case, both wings of an avian predator often touch the surface of the snow, allowing you to measure the wingspread, and this information can help to eliminate some species of raptors. Birds of prey often defecate at a kill site. In the lower left corner of the photograph, as well as to the left and right of the packed area where the squirrel was eaten, you can see white (uric acid) bird droppings. Given that it is a hawk or an owl, knowledge about their respective evacuation habits will allow you to narrow down the possibilities even further. Owls tend to let their droppings do just that – drop, leaving small plops on the ground. Hawks, on the other hand, tend to forcefully eject their droppings some distance away. The long, thin streaks at this site were definitely propelled outwards, making it likely that the predator was a hawk. Familiarity with the hawks that overwinter in your area can help pinpoint which species it could be.

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Canada Lynx “Snowshoes”

12-16-13 lynx & bobcat feet IMG_3811Bobcats and Canada Lynx are in the same genus, and are roughly the same size (averaging 15 to 35 pounds), with Bobcats usually weighing a bit more than Lynx. The size of their feet is vastly different, however, and not proportional to their relative weights. A Lynx has much larger feet and longer legs than a Bobcat. Its range extends further north, which means it must be well equipped to deal with snow much of the year. A Lynx has big, furry paws, and when its feet land the toes spread way out. Both of these adaptations help a Lynx’s feet act like snowshoes, helping it to chase down food in the winter. Much of the time, this food consists of Snowshoe Hares –anywhere from 60 to 90 percent of the diet of Lynx is made up of hares. The soles of Snowshoe Hare feet are also well-furred, particularly in winter, enabling them to run on soft, deep snow without sinking in very far. Because Snowshoe Hares are extremely fast and agile (reaching speeds of 30 mph and jumping 12 feet in a single bound), the feet of any serious predator must also be well adapted to traveling on snow.

Note: Bobcat sightings are much more frequent than Lynx in northern New England (the southern tip of the Lynx’s range) but breeding populations of Lynx have been documented in the last two years in the boreal forests of Maine, New Hampshire and Vermont.

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Eastern Chipmunks “Clucking”

10-2-13 eastern chipmunkIMG_3035Especially in the fall, and sometimes in the spring, the woods are full of “clucking” Eastern Chipmunks. It’s unusual to hear this call during the summer, but once leaves have started to fall off the trees, giving chipmunks a clearer view of the sky, the chorus begins. One chipmunk starts calling, and the message is passed on to other relatives, who join in. These vocal little rodents are warning each other of the presence of an aerial predator, perhaps a hawk or day-hunting owl. The next time you hear this distinctive alarm call, look skyward. You may well be rewarded with the sight of a raptor flying overhead.

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Cerceris fumipennis: a biosurveillance tool for the emerald ash borer

8-19-13 Cerceris wasp with beetle prey2 099While we’re more familiar with social wasps, such as paper wasps, yellow jackets and hornets, there are also parasitic and solitary wasps. Solitary wasps live alone (as their name implies), all the females (not just the queen) are fertile and they are predatory. Among them is a wasp, Cerceris fumipennis, which preys exclusively on the family of beetles (Buprestidae) to which the Emerald Ash Borer (EAB), the invasive beetle that’s threatening the ash tree population, belongs. After catching and paralyzing its prey, the wasp carries it back to her larvae in the nest she’s dug underground. A biosurveillance program exists which involves monitoring the prey that this species of wasp collects and brings back to the nest, in order to detect the presence of the Emerald Ash Borer in any given area. (This is how the EAB was first detected in Connecticut.) Pictured is a Cerceris fumipennis wasp with a Buprestid beetle (not an EAB) prey. (To become involved in Vermont’s citizen science biosurveillance program next summer, contact entomologist Trish Hanson of the Vermont Dept. of Forests, Parks and Recreation at Hanson.Trish@state.vt.us .)

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Woodland Jumping Mouse Succumbs

8-13-13  woodland jumping mouse134Usually animals that have been killed don’t last long enough for humans to discover them unless the human disturbs the predator right after it’s killed its prey. This may well have been the case when I came upon this Woodland Jumping Mouse. It is actually fairly unusual to set eyes on a jumping mouse, dead or alive, as they are quite secretive. This remarkable one-ounce rodent has long hind feet and a distinctly long tail, which makes up more than half of its total length of eight to ten inches. Using its hind limbs for propulsion and its tail for balance, the Woodland Jumping Mouse is able to make large leaps of up to eight feet or more to escape danger. (More often it walks around on all fours, or uses short hops for greater speed.) Another survival strategy that jumping mice use is to remain motionless for up to several hours, relying on their coloration and cover for protection. Apparently neither adaptive behavior was effective enough to spare this mouse’s life.

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Backswimmers

Backswimmers are aquatic insects that seek out prey as large as tadpoles and small fish. They row around ponds with their fringed hind legs and grasp prey with their front pair of legs. The piercing mouthparts that they use to kill their prey are also capable of giving humans who handle them carelessly a nasty bite (they are also known as “water wasps” for this reason).7-12-13  backswimmer 376 Because they spend most of their time on their back, their coloring is opposite that of most insects – backswimmers typically have a dark belly and a light-colored back, making them less conspicuous to predators (and prey) both above and beneath them. These tiny bugs can stay submerged for hours thanks to their ability to store air bubbles in two channels on their abdomen which are covered with inward-facing hairs. Backswimmers are often confused with Water Boatmen, which are not predaceous, do not bite, and swim “right side up.” Water Boatmen’s dark color and parallel lines on their backs help distinguish them from Backswimmers.


Common Loon Chick Meal Delivery

7-10-13 loon chick being fed 119For the first few days of a loon chick’s life, both of its parents are ever-present, catching and delivering small fish, crayfish and invertebrates for their one or two chicks. Their initial buoyancy and their lack of experience prevent the chicks from procuring their own food for the first month or so, although they soon learn how to chase fish. During the first couple of weeks, the parent loon, having caught a crayfish, small fish or other prey, swims right up to its young and offers the chick its next meal. The chick grasps the food while it is still in its parent’s beak. The parent lets go, and the chick attempts to swallow the crayfish (in this case). In the beginning, the chick often drops its meal. The parent then dives down to retrieve it and once again offers the same crayfish to the chick. This sequence of events can happen over and over until the chick finally manages to hold onto and shift the crayfish into a head-first position in order to swallow it. By the third week this beak-to-beak service begins to be replaced by a practice designed to teach the chick how to capture its own meals. The parents start dropping the food they’ve caught for their chick into the water in front of them, forcing the chick to dive and develop the skills necessary for survival. (The pictured loon chick is well into its second week. Close examination reveals that the chick’s “egg tooth,” used to exit the egg, is still present at the tip of its beak. By week #3 it is not evident.)


Dragonfly Eyes

7-8-13 dragonfly eyes2 381Dragonflies (and bees) have the largest compound eyes of any insect, each containing up to 30,000 facets, or ommatidia (house flies have 6,000). Each facet points in a slightly different direction and creates its own image, and the dragonfly’s brain compiles these thousands of images into one picture. This eye structure enables dragonflies to be extremely sensitive to motion. Because a dragonfly’s eyes wrap around its head, it can see in all directions at the same time (though its forward-looking vision is the sharpest). When capturing prey, a dragonfly doesn’t chase it – it intercepts it in mid-air, and it’s successful nearly 95% of the time. This hunting technique entails calculating the distance of its prey, the direction it’s moving and the speed that it’s flying – an impressive feat any tennis, baseball or football player would especially appreciate!

(Photo is looking down on the eyes of a Common Green Darner. Three simple eyes, or ocelli, are located in the black section below (above in the photo) its two tan compound eyes. The short, thin black lines are its antennae, which can detect wind direction and speed. The yellow section is part of the upper half of its face, or frons.)


Moth Eyes and Biomimicry

7-1-13 luna eyes 020Because moths need to use every little bit of light available in order to see in the dark, their eyes are highly non-reflective. (This is also helpful in decreasing the chances of predators spotting them.) Scientists, through biomimicry, have come up with a number of technological advances, including the development of a film that can be applied to solar cells which helps keep sunlight from being reflected off of them before the light can be utilized. Man-made materials based on the structure of moth eyes could someday reduce the radiation dosages received by patients getting x-rayed, while improving the resolution of the resulting images. Research on recreating the pattern found on moths’ eyes onto plastic could lead to reflection and glare-free display screens for televisions, cell phones, computer monitors, eyeglasses, speedometers and more.