“here’s looking at you”

With huge, globular eyes that make up about 50% of their head, dragonflies are amazing visual predators.

dragonfly eyes

A sampling of beautiful dragonfly eyes from a Google search

And those eyes are key to their success as highly visual predators.

halloween pennant-8111

Halloween Pennant dragonflies search from the tips of the highest plants in grassy fields, with their orange-banded wings fluttering in the breeze.

In fact, they are probably the most efficient predators in the animal kingdom, with an astounding 95% success rate per attempt.  In comparison, lions are lucky to succeed once every four to five tries and great white sharks only manage to catch what they are after half the time.  How do dragonflies do it?

Here's looking at you...

Here’s looking at you… the facial disk of the Horned Clubtail.  Depending on the angle of incoming light (and observer position), the eyes might look turquoise blue.

Enough clues? The eyes and more particularly, the wiring of retinal cells to the brain is key to their hunting success.

The eyes and more particularly, the wiring of retinal cells to the brain, is key to their hunting success.

Those giant optical domes on the top of their heads give them a 360 degree view, and contain as many as 30,000 optical units (ommatidia), each with a complement of photopigments that can process images separately.  Thus, instead of one retinal focusing area, they have thousands.

The eye of a dragonfly, showing the individual facets or ommatidia that contain visual pigments. Each facet can detect and send an image to the insect's brain. Imagine having 30,000 eyes!

The eye of a dragonfly, showing the individual facets or ommatidia that contain visual pigments. Each facet can detect and send an image to the insect’s brain. Imagine having 30,000 eyes! From Science Blogs, July 8, 2009.

In addition, where human eyes have three photo pigments, dragonflies have 15-30 pigments that can detect light in ranges beyond human capability, including detection of polarized light.  What if we could see images in UV or infra-red, or whatever other spectral wavelengths dragonflies can resolve?

A newly emerged male Common Whitetail has the wing markings of a male and the abdominal coloration of the female. Over the course of the next week, he will gradually transform to the powder-white abdomen typical of males.

A newly emerged male Common Whitetail has the wing markings of a male and the abdominal coloration of the female. Over the course of the next week, he will gradually transform to the powder-white abdomen typical of males.

Photopigments sensitive to blue and UV light are concentrated in the upper part of the compound eye, so that prey (or predators) above them stand out against a perceived white background.  Pigments sensitive to longer wavelengths (green, yellow, red) are concentrated in the lower part of the compound eye and allow prey flitting below the dragonfly in dense vegetation to be detected.

This Dot-tailed Whiteface continually moved its head up and down as it scanned for prey. Each time I tried to get in front of it to photograph its white face, it flew away.

This Dot-tailed Whiteface continually moved its head up and down as it scanned for prey. Each time I tried to get in front of it to photograph its white face, it flew away.

In addition to their heightened visual sensitivity and acuity, dragonflies exhibit single-object tracking, which means they keep a particular prey item exactly on a collision course with themselves. (Kind of sounds like a drone, doesn’t it?)

And that’s where the fancy flying comes in handy. To keep the image of the prey in exactly the same place in their visual field, a dragonfly might fly up, down, sideways, backwards, even upside down, if needed. Four wings that can move independently facilitate this maneuverability, and in fact, they don’t even need all four.

This female 12-spotted Skimmer has lost half of its hind wing, but it's doubtful that it comprises hunting success.

This female 12-spotted Skimmer has lost half of its left hind wing, but it’s doubtful that it comprises hunting success.

These amazing little machines have been around for several hundred million years, feasting on slower flying, less visually talented prey.  Such a visual formula for hunting success ensures that they will be around for a while, keeping those pesky mosquitoes in check.

[This is an edited version of a previous post from Backyard Biology]

baby, it’s hot out there

This week’s extreme heat (high 90s) and high humidity (felt like 90%) are what makes us grateful for MN winters…I guess.  There wasn’t much activity in the backyard today, with a only a few birds visiting the feeders and a few bumblebees buzzing in the garden.  Dissipating heat is hard for endotherms that generate heat through their metabolism, so it makes sense to find shade, or increase evaporative cooling with a nice bath.

catbird-

Ah, a little soak to cool off a hot Catbird.

catbird-

Getting wet all over is even better.

catbird-

Feeling much cooler, now to find a perch in the shade and wait out the daytime heat wave.

But even the low metabolic ectotherms were fighting the solar load, like this female Blue Dasher dragonfly that tipped her abdomen toward the sky to block the heat radiating down on her sensitive head.

female blue dasher dragonfly

This little dragonfly can reduce its heat load by positioning the slender abdomen up into the “obelisk position”.

female blue dasher dragonfly

What pretty eyes they have — red on top, pale blue on the bottom.

Getting into focus

Last year’s big Christmas present was a new macro lens, which I didn’t get around to using until spring, because frankly it was too cold to try macrophotography outdoors last winter.  Apparently, I didn’t use it very much even then, because it was much easier to select the top ten “small things” photos than it was for the birds. But here they are — the top 10 macro shots of 2014, chosen for their color, variety, and potential biological interest.

orange-bluet-male

An Orange Bluet male on a smooth, contrasting background of green.  I never saw one like this again, after I took this photo.

black-swallowtail-on-dutchmans-breeches

The contrast of black in the Black Swallowtail on the white of the Dutchman’s Breeches was the basis for this choice.  Finding nectar in early spring can be a challenge for early emerging butterflies.

In contrast to the shot above, the Tiger Swallowtail in a sea of summer wildflowers is quite colorful.

In contrast to the shot above, the Tiger Swallowtail in a sea of summer wildflowers had numerous choices from a variety in the wildflower garden.

squash borer moth

It’s difficult to choose such a noxious pest insect like the Squash Borer Moth for this collection, but it is a colorful insect caught in mid-flight (in focus!)

Clearwing hummingbird moth

Another moth, rarely seen at rest — the Hummingbird Clearwing Moth (Hemaris thysbe).

band-winged meadowhawk

One of several species of meadowhawks difficult to tell apart in their juvenile stages. They were very abundant in the wildflower garden this summer, hopefully gobbling up the many mosquitoes there.

sweat bee on spiderwort

I never realized what a popular flower Spiderwort is to insects. The Green Sweatbees, hoverflies, and bumblebees stocked up on its pollen in early spring.

leadplant flower moth, Schinia lucens (1)

Another rare visitor to the back yard (well, really a neighbor’s front yard) was this Leadplant Flower Moth, a specialist on said plant.  Read more about it here.

female black horse fly mouth parts

If you have ever been bitten by a 2-inch horsefly, here’s why it hurt. Those are a couple of shearing scissors up front in its mouthparts.

milkweed leaf beetles (Labidomera sp.) mating

And lastly, the colorful Milkweed leaf beetles attempting to mate on a milkweed leaf. It’s more of a humorous shot really, since this male tried every which way to get into position.

Meadow dragons

Meadowhawks are small-bodied dragonflies, about the length of a damselfly, but stockier in mid-body and with longer and wider wings.  They are indeed hawks of the meadow, as they chase flies and mosquitoes around, and so I welcome them in my backyard.

Meadowhawks and Northern Bluet Damselflies gather on the wildflowers in the garden in the early morning.

Meadowhawks and Northern Bluet Damselflies gather on the wildflowers in the garden in the early morning, waiting for the mosquitoes to arrive.

There are over 60 species in the meadowhawk (Sympetrum) genus, spread over the temperate zone of every continent except Australia, and many of them look a lot alike. Complicating identification even further is the variation in color markings on wings and abdomen that may change gradually over the summer and may differ between the two sexes in one species.

For example, I took photos of several of the orange-colored meadowhawks flying around my garden yesterday morning and this is what I saw when I loaded the photos on my computer:

The Band-winged Meadowhawk is aptly named for the amber patches on its wings.

There was one with wings tinted with amber.  Is this a Band-winged Meadowhawk or is it a female Cherry-faced Meadowhawk, which also exhibits the amber wing patches?

In side view, you can't see the amber patches, but the face color is definitely yellow-tan.

In side view,  the amber patches on the wings are not so obvious, but note the yellow-tan face color of this dragonfly compared to the one directly below.

This one looks very similar to the one in the last photo, but the face is much whiter.

This one looks very similar to the one in the last photo, but the face is much whiter and there are no amber patches on the wings.

And just to add to the conrfusion, yet another orange meadowhawk with some amber on its wings, but not as much as the first one.

And just to add to the confusion, yet another orange meadowhawk with some amber on its wings, but not as much as the first one.

At this point, I gave up on trying to identify what I saw.  These are simply meadowhawks — they may the same species, or they might be two or three different species. They don’t look very different to me, but I’ll bet female meadowhawks are very discriminating about which males they allow to mate with them. Using just one highly variable character like amber patches on wings, it’s easy to see how such variation of form might have led to the diversity of species over time in just this one genus of dragonflies.

a prairie walk – part 2

Only a week after our first trip to the Glacial Lakes area prairies, we saw new plant species flowering and a different set of animal species moving about.  My expectations were low because of the lousy weather (storms), but that didn’t seem to affect the wildlife — in fact, it seemed animals were on the move, perhaps trying to tell us to get out of the way of the weather!

Dragonflies weren't numerous, but there were a few species I had not seen yet in my own backyard, like this 4-spotted Skimmer.

Dragonflies weren’t numerous, but there were a few species I had not seen yet in my own backyard, like this 4-spotted Skimmer.  It indeed has four spots on its wings, but there are two additional spots near the abdomen (making this a 6-spotted Skimmer instead).

The Dot-tailed Whiteface is well-named for its standout features and were more numerous than other dragons.

The Dot-tailed Whiteface is well-named for its standout features and were more numerous than other dragons. The male has a singular square-shaped dot on its abdomen; females have several more dots, but keep the terminal square-shaped one.

Both of these dragonfly species were far from water, hovering over vegetation on the dry prairie, perhaps in search of the numerous mosquitoes there.

I flushed a Lark Sparrow from the ground and was certain it was sitting on a nest there, but couldn't find it.  The bird sat in a tree 100 feet away and chipped at me.

I flushed a Lark Sparrow from the ground and was certain it was sitting on a nest there, but couldn’t find it. The bird sat in a tree 100 feet away and chipped at me.  What a striking little sparrow with its dark facial and crown stripes and black dot on its breast.

Lark Sparrows are commonly found in farm fields and grasslands.  They have the unusual habit of taking over taking over old mockingbird or thrasher nests as its own — sometimes before the previous owner has finished incubating its eggs. The male struts around like a turkey during courtship, erecting and fanning his tail feathers and drooping his wing feathers to the ground, before presenting the female with a twig as her copulatory gift.

We saw numerous flocks of White Pelicans and Double-crested Cormorants flying in V formation overhead away from the incoming weather front.  Later that day we heard there were tornadoes sighted just a few miles away.

We saw numerous flocks of White Pelicans and Double-crested Cormorants flying in V formation overhead, away from the incoming weather front. Later that day we heard there were tornadoes sighted just a few miles away.

Animals can sense the radical changes in barometric pressure that precede extreme weather — meaning, we should pay attention to their behavior and seek shelter as well.  Some animals can also hear the infra-sounds (ultra low frequency) produced by stormy weather, earthquakes, or flash floods occurring far away.  Another good reason to watch what they are doing.

Blue Flag Iris were blooming in the wetter areas of the prairie.

Blue Flag Iris were blooming in the wetter areas of the prairie.  Blue Flag is a tall, showy plant that grows in clumps in roadside ditches, wet meadows, and along lake shorelines, often even in standing water in the northeastern U.S. and eastern Canada.

Prairie Larkspur is diminutive compared to the horticultural variety we have in our gardens.  Small, white flowers on a tall, slsender stalk stand out among the prairie grasses though.

Prairie Larkspur is diminutive compared to the horticultural variety we have in our gardens. White, spurred flowers on a tall, slender stalk stand out among the prairie grasses though.  Flower stalks might stand 3 feet tall and support as many as 30 flowers — very attractive to bumblebees.

Prairie Phlox has sticky stems and leaves, a sweet smell, and an attractive landing platform for its butterfly pollinators.  In the right moisture conditions, it can form dense clusters of dozens of flowers to attract its pollinators.  A tiny Syrphid fly (upper left) was the only visitor seen this day.

Prairie Phlox has sticky stems and leaves, a sweet smell, and an attractive landing platform for its butterfly pollinators. Under the right moisture conditions, it can form dense clusters of dozens of flowers to attract its pollinators. A tiny Syrphid fly (upper left) was the only visitor seen this day.

Bright pink flowers of the Prairie Rose lend color to the grassy matrix of the prairie.  Its fruits (rose hips) are rich in vitamin C, which humans (e.g., Native Americans) need, but other animals enjoy as sweet additions to their diet.

Bright pink flowers of the Prairie Rose lend color to the grassy matrix of the prairie. Its fruits (rose hips) are rich in vitamin C, which humans (e.g., Native Americans) require, but other animals enjoy the entire plant as good forage.

Junegrass is one of the early blooming native grasses on the prairie.   Because it blooms early, it is especially sensitive to grazing pressure.  Other, taller native grasses won't bloom for another month or more.

Only a foot or two tall, Junegrass is one of the early blooming native grasses on the prairie.

Native prairie grasses (“warm season grasses”) spend much of the summer growing tall before they send up a flower spike in late summer.  European immigrant farmers seeded the prairies with “cool season” grasses from their native countries so their livestock would have good nutrition throughout the spring and summer.  Because Junegrass blooms early, it is especially sensitive to grazing pressure.

Macro-ed

On a cool morning recently, the dragonflies were a bit comatose sitting on the leafy vegetation in the backyard, waiting for some sun to heat them up.  They let me get really close to take full advantage of my macro lens magnification.

The Horned Clubtail dragonfly face resembles a monkey's, with its widely spaced goggle eyes and big broad lips.

The Horned Clubtail dragonfly face resembles a monkey’s, with its widely spaced goggle eyes and big broad lips.  Clubtails are one of only two groups of dragonflies that have their eyes so widely separated.  A tall, plate-like yellow shield between the eyes is typical of this species.

Black bumps between the eyes are motion-detecting ocelli (singular, ocelllus).  Each compound eye contains more than 30,000 light-sensing photoreceptors (ommatidia), giving this highly specialized predator incredible visual acuity in all directions.  For more detail on the marvels of dragonfly vision, see my earlier post on this subject.

From this angle it looks like the dragonfly wears transparent helmets over its eyes.

Viewed from the top, the transparent-looking shields only cover the front of the eye.

Viewed from the top, the transparent-looking shields cover only the front of the eye.  I admired the intricate pattern of yellow and black on the head and thorax of this female Horned Clubtail, which allow us humans to tell species apart — but what do they mean to another dragonfly?

Some dragonflies species are like some bird species with sex-dependent color patterns that distinguish male and female from one another.  Horned Clubtail males and females look alike, except for the business end involved in reproduction.

The male's terminal segment (the cerci) have curved spikes resembling cow horns (hence, the species name), used to grab the female's head during mating.

The Horned Clubtail male’s terminal segment (the cerci) have curved spikes resembling cow horns (hence, the species name), used to grab the female’s head during mating. (This shot taken with the Canon 100-400 telephoto lens.)

The Horned Clubtail female's terminal segment shows short, straight cerci used in egg-laying.

The Horned Clubtail female’s terminal segment shows short, straight cerci used in egg-laying. (This shot taken with the 90 mm Tamron macro lens.)  It looks like there are fine hairs that project from the surface of the abdominal segments — I’ve no idea what they are for.

Comatose dragonflies make great subjects for macro photography, revealing details of structure I’ve never seen or thought about before.

Orange is the new “blue”

Every time I look out at the goldenrod in the backyard, I see new species of damselflies there.  This one was really striking with his bold orange and black thorax and orange eyes.  I should have mentioned (yesterday) that I have finally begun using the new macro lens I got last Christmas, and what a difference it makes when you’re trying to photograph something that is only 1-1.5 inches long.  (Click on any of the photos below for larger and sharper views.)

An Orange Bluet male.... really!  This is not your everyday blue Bluet.

An Orange Bluet male…. really! This is not your everyday average blue Bluet.

There are scarlet, cherry, and burgundy Bluet damselflies as well — how confusing.  I wonder why they didn’t call this one the Halloween Bluet instead.

The frontal view provides a better look at his orange and black thorax, and orange and burgundy eyes.  What a face!

The frontal view provides a better look at his orange and black thorax, and orange and burgundy eyes. What a face!

The females of this species are variable in color:  they might be yellow, green, or blue and black which makes it difficult to ID them.  However, they are usually not seen unless they are being carried around by a male in tandem flight.  Unlike most dragonflies that lay eggs underwater while dangling from a stem above it, the Orange Bluet female deposits her eggs on twigs while immersed in the water, with the male accompanying her in their underwater mating dance.

Those bright orange post-ocular spots look like stop lights.  The eyes seem to be three colors ranging from burgundy above to tan below.

Those bright orange post-ocular spots look like stop lights. The eyes seem to be three colors ranging from burgundy above to tan below.  Some wickedly sharp spines on his legs are probably used to snare insects.

What a gem!   I wonder what I’ll find out in the goldenrod patch tomorrow.

Damsels in the backyard

In the two weeks we have been gone, our Minnesota backyard has transformed from early spring to early summer.  The perennials have shot up at least two feet, and there are quite a few insects flitting about.  Today, the damselflies were almost as thick as the mosquitoes, as they cruised from leaf to leaf.

Male and female Northern Bluets (I am guessing) congregated like hands on a clock face on the new leafy growth of the goldenrod stems.

Male and female Northern Bluets (I am guessing) congregated like hands on a clock face on the new leafy growth of the goldenrod stems.

Male Northern Bluets are easily recognized by their striking blue patterned bodies.  Fortunately, Minnesota is home to only three bluet damselfly species, making ID a little easier.

Male Northern Bluets are easily recognized by their striking blue patterned bodies. Fortunately, Minnesota is home to only three bluet damselfly species, making ID a little easier.

Female Northern Bluet damselflies lack the blue coloration on eyes, thorax, and abdomen, as well as the signature blue spot at the tip of the abdomen.

Female Northern Bluet damselflies lack the blue coloration on eyes, thorax, and abdomen, as well as the signature blue spot at the tip of the abdomen.  Notice how the color of the post-ocular spots (behind the eyes) matches the color of the thoracic stripes on both the male and female.

This is a truly wide-ranging species, found throughout the northern hemisphere in North America, Europe, and Asia, but ranging as far south as India and Mexico. They appear early in the spring and are active until late summer, probably one of the most common damselflies seen.

Damselfly ID guides say that the Northern Bluet is highly variable in its blue color pattern.  But this must be another species, and its color pattern doesn't match any of the MN damselfly species.  Help me out here, if you know what this is.

Damselfly ID guides say that the Northern Bluet is highly variable in its blue color pattern. But this must be another species, and its color pattern doesn’t match any of the MN damselfly species. Help me out here, if you know what this is.

Eastern Forktail Damselfly males were found right alongside the Bluets.  Their distinctive green and black thoracic stripes and bright blue spot at the end of the abdomen, as well as slightly larger size, distinguished them from the more common bluets.

Eastern Forktail Damselfly males were found right alongside the Bluets. Their distinctive green and black thoracic stripes and bright blue spot at the end of the abdomen, as well as slightly larger size, distinguished them from the more common bluets.

Eastern Forktail damselflies are common throughout the north and eastern U.S., ranging as far south and west as Oklahoma.  Thoracic stripes in females may be yellow-green to yellow-orange, but I didn’t see any of these among the Goldenrod leaves, so perhaps they have not emerged yet.  Females begin mating within a few days of emerging, and lay eggs within a few hours of mating. Unlike most Odonates (dragonflies and damselflies), Eastern Forktails are monogamous, and all of the female’s eggs are fertilized by just one encounter with a male.

The Best of 2013

Highlights of 2013 in Backyard Biology:

Ballet of the Swan - January 19, 2013

Trumpeter Swans at Lake Vadnais, St. Paul, MN – January 19, 2013

Spring Turkeys - March 23, 2013

Turkey in the snow – March 23, 2013

Regal Red Fox - April 4, 2013

Red Fox and kits – April 4, 2013

West Indian Woodpecker - May 1, 2013, from Cayo Coco, Cuba

West Indian Woodpecker – May 1, 2013, from Cayo Coco, Cuba

Horned Clubtail dragonfly - June 22, 2013

Horned Clubtail dragonfly – June 22, 2013

Cottonwood prairie SNA - July 28, 2013

Cottonwood prairie SNA – July 28, 2013

Ruby-throated Hummingbird approaching Cardinal flower - August 17, 2013

Ruby-throated Hummingbird approaching Cardinal flower – August 17, 2013

Bishop Pass on the Pacific Crest Trail, Sierra Nevada Mts. - September 17, 2013

Bishop Pass on the Pacific Crest Trail, Sierra Nevada Mts. – September 17, 2013

Red-bellied woodpecker storing acorns for the winter - November 8, 2013

Red-bellied woodpecker storing acorns for the winter – November 8, 2013

Coyote in the backyard - December 15, 2013

Coyote in the backyard – December 15, 2013

Happy New Year to all!

Last chances

The weather is headed toward cooling, the light is waning and the sun doesn’t clear the tops of the trees in the backyard anymore, but still there are various species of meadowhawks in the marshes and ponds trying to ensure the survival of the next generation.

A Yellow-legged Meadowhawk (Sympetrum vicinum) staked a claim on this bare branch. This is one of the more commonly seen "red meadowhawks" that hang around until freezing weather in November. They are often found in the very low vegetation, but perch higher as the temperatures warm up during the day.

A Yellow-legged Meadowhawk (Sympetrum vicinum) staked a claim on this bare branch. This is one of the more commonly seen “red meadowhawks” that hang around until freezing weather in November. They are often found in the very low vegetation, but perch higher as the temperatures warm up during the day.

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Yellow-legged Meadowhawks are tiny (1+ inch) and become redder with maturity in both sexes. One of the last dragonflies to emerge in the late summer, often not breeding until late August, they may be the last dragonflies seen in the fall.

Another late developer often not seen until fall, the Saffron-winged Meadowhawk (Sympetrum costiferum) also has a mostly plain red abdomen in the male, while the female is brownish-gray. This species has black legs and amber-tinted veins in the anterior parts of the wings, making it rather easy to distinguish from the Yellow-legged Meadowhawk.

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I found this couple flying poorly from site to site in the litter near a large lake.  Dragonflies in this “wheel position” would seem to be vulnerable to predation, as their mobility is markedly reduced.

In case you have ever wondered what is going on here:  (skip this part if insect reproduction is not your cup of tea…)

A male dragonfly flexes his abdomen forward and deposits a packet of sperm in a chamber under and just behind the junction of his thorax and abdomen.   Claspers at the tip of his abdomen (called cerci) grab and hold the female behind her head, while she extends her abdomen forward to retrieve the sperm packet through an opening at the tip of her abdomen.

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Colorful red dragonflies on colorful fall leaves.

Once copulation is complete, males may fly around with the female in tandem, still latched onto her head with his cerci, while the female deposits her eggs in the stems of aquatic plants, or under floating logs, or near the shoreline.  This insures that it is his sperm that will contribute to the fertilization of those eggs.

You might wonder if dragonflies ever make a mistake and hook up with the wrong partner, since one red dragonfly seems to look just like another.  However, it seems that females are very discriminating and choosy, and will not extend their abdomen toward the male’s genital area if they don’t like the behavior they see in a potential mate.  A familiar story in many species.