The beginning of spring, by which I mean the arrival of the rainy season, is one of my favorite times of year here in south Florida. The damselflies and dragonflies are out in significant numbers again, dotting the grasses and trees searching for food. Earlier this week there were dozens of dragonflies cruising the back yard, among them some pretty Needham's Skimmers and the eye-catching little pennant, Celithemis eponina, commonly known as the Halloween Pennant for its festive orange and black (well, a brown so dark that people call it black, like my dad's hair back before he became a silverback) colors. Julius Sabinus, a Gaulish chief who attempted to overthrow the Roman occupation and was forced to flee, enduring a decade of privation and hardship, alleviated only by the devotion of his wife. When they were finally captured and sent to Rome, Vespasian executed Sabinus, and Eponina asked to be executed as well, a request that was granted. Plutarch called this the darkest deed of Vespasian's reign, "there was nothing during Vespasian's reign to match the horror of this atrocious deed, and that, in retribution for it, the vengeance of the gods fell upon Vespasian, and in a short time after wrought the extirpation of his entire family." The English name for this genus, the pennants, is also descriptive: it refers to their habit of perching, flag like, on vertical stems. And, if you'll recall, pennants are small flags, appropriate because most species in this genus are rather small. References Paulson, D. R., and S. W. Dunkle. (2012). A Checklist of North American Odonata, including English name, etymology, type locality, and distribution. Available online at http:odonata.bogfoot.net/docs/NA_OdonataChecklist_2012.pdf Paulson, D. (2011). Dragonflies and Damselflies of the East. Princeton: Princeton UP.This is one of the smaller dragonflies around, though nowhere near as small as the diminutive Little Blue Dragonlet that is also rather common in our back yard at this time of year. It's also, like its cousin the Blue Dasher, rather confiding. It's not too difficult to sneak up rather close to one, which can result in some rather pretty photos: It has some characteristic poses, as well. It likes to perch with its head and abdomen well below its thorax, as you might be able to tell from the picture above (notice how the wings are in focus, the head is slightly out of focus, and the abdomen gets progressively blurrier as you look toward its tail?). The picture above also lets you know that this, like most of the dragonflies hanging out in a suburban back yard not on water suitable for reproduction, is a young dragonfly. If it's a male, that broad yellow stripe down its back will gradually turn reddish-orange as he ages; if it's a female, the dark sides of the abdomen will turn "pruinose" or powdery white. The characteristic "pennant" poses that give this dragonfly its name become even more obvious in other situations, though, such as when it has all of its wings compensating for the breeze attempting to shake it off the rather flimsy perches it affects: But what truly makes it a photographer's dream is its willingness to allow a close approach: The shot above was from about a foot away; such a close approach lets you crop and enlarge to your heart's content. So for those of you who just can't get enough of those cute little dragonfly faces, here's another one for you: Etymology The genus name, Celithemis, is a combination of the Greek words kelis, spotted (referring to the wing spots on most members of the genus), and themis, law, decree, order, presumably because this genus can be "ordered" or classified according to the pattern and number of spots on the wings, which are diagnostic. Eponina, the specific name, was the wife of
South Florida is typically described as having two seasons: wet (May through October) and dry (November through April). Hydrologists like to split this up a bit further, with the wet season (now called high rainfall, low evapotranspiration season) running June through October, and the dry season now divided into two subseasons: low rainfall, low evapotranspiration (November through February) and a low rainfall, high evapotranspiration season (March through May). What this translates to in layman's terms seems to be something like "wet, then dry, then really dry." Over the last three years, two Aprils have been fairly wet (7.5 inches at my rain gauge this year, and a whopping 9.22 inches the previous year), while one was quite dry (in 2011 we had only 1.15 inches of rain in April). This year, May started off with a bang: Over six inches of rain in the first three days, five and a half of them in one long rainy day that also included at least one tornado here in Boca Raton (at my dentist's office, no less!). All that moisture falling from the sky, saturating the local soil, has an effect on wildlife. Saturday morning, after what seemed like forever, the yard was full of odonates again. Damselflies (Rambur's Forktails, Fragile Forktails, and Everglades Sprites) and dragonflies both (Blue Dasher, Little Blue Dragonlet, Eastern Pondhawk) were flitting around in the tall grass (after months without having to mow, I can see that I'll be back out on a weekly basis with my trusty reel mower—no gas for me!). Here's a shot I liked of one particularly patient Everglades Sprite (Nehalennia pallidula): As usual, you can click on the image for a larger view. If you look closely, you can see the individual facets in the right eye: As you may recall, those individual facets in the compound eye are called ommatidia. These tiny simple lenses, in combinations of hundreds (in the simplest compound eyes) to tens of thousands, form a complete image in the brain of the animal. The more ommatidia there are, the greater the visual acuity of the animal in question (in addition to insects, millipedes and mantis shrimp have compound eyes featuring ommatidia). In that respect, they function very much like the pixels on a CCD chip: as you add more pixels to your camera, you can create larger and larger images at high resolution. (Can you tell I got a new camera recently? One with a ridiculously high pixel count?) Another damselfly appeared a bit after I got tired of chasing those sprites around. This one is a Fragile Forktail (Ischnura posita): And there was the ubiquitous Rambur's Forktail as well: Here's the first dragonfly I've managed to image so far this month; the Blue Dasher (at one point the most commonly photographed odonate on odonatacentral.org): And here's the second. (Surprise, surprise! Another Blue Dasher): And the third, a different species this time (Little Blue Dragonlet): If this keeps up, it might be an interesting season for backyard wildlife after all!
Last week I started to notice the persistent presence in these here parts of those ephemeral and infernally hard to see odonates, the damselflies. Two forktail species, Rambur's and Citrine, (Ischnura ramburii and I. hastata, for those of you keeping score at home) are the only ones present so far, but I'm sure that soon I'll see the bluets again. I'm generally only able to go out on photo safari during the lunch hour (I do have a day job, after all), and I've found that the local damselflies are pretty wary in the middle of the day. But the other afternoon I was able to sneak up on one bright yellow male Ischnura hastata (Citrine Forktail); it was quiescent enough to allow me to discover the effects of depth of field on odonate photography. These animals are small, but in macro photography, small distances matter. As Sid Dunkle, coauthor of the recent monographic guide to the damselflies points out, depth of field is critical to successful odonate photography. In the photographic Supplement to Damselflies of North America, the standard treatment of the zygoptera, Dunkle writes that
I have had the near eye and the tip of the abdomen of a damselfly in focus, but the near surface of the thorax was out of focus! ... The film plane [or in my case, the CMOS chip] must be aligned exactly with the longitudinal axis of the body to get both head and tip of abdomen in focus. A lot of patience is needed!In my case, patience was needed simply to approach these maddeningly elusive little beasts. I say maddening because one would expect that a relatively large and slow-flying animal like this would be pretty easy to keep track of once spotted. But nothing could be further from the truth. It might just be my aging eyes, but I found it quite difficult to keep my eye on these little buggers as they flew from brightly lit areas to shade, and from grass stem to grass stem. At times I found it easier to track them by their shadows than by their actual bodies! But once you get a damselfly quiet, it is indeed possible to approach them closely enough to capture some successful photographs, as the gallery below indicates. It's also possible to discover just how critical focusing is in macro photography.
I took many more than seven photos, of course; these are just the ones that are anywhere close to being keepers, or that can serve as instructional reminders for myself.
The first few days of fall in Florida often bring cold (well, cool) fronts to the region. This year we're already on our second or third round of long-sleeve days, so I thought this might be a good time to show off what I've been able to capture of the cold-slowed insect fauna. Here's a photo from last week; it's the Blue Dasher (Pachydiplax longipennis) with the messed-up wing from the front porch. The Blue Dasher is a member of a monotypic group (which just means that, like Tigger, the wonderful thing about the Blue Dasher is it's the only one of its kind) in the skimmer family (Libellulidae). Despite its lack of close cousins, it's one of the most widespread and common dragonflies in North America. Back in 2010, it was the most commonly submitted record at Odonata Central, with 368 records (2.3% of the total). [Note: A search of that site today reveals that there are now 1602 records of this species on the site, but it's been outstripped in popularity by the previous number 2 species, Eastern Pondhawk (Erythemis simplicicollis), with 1680 records as of today.] fabulous Wikipedia image, are the three ocelli of Aeshna cyanea. The prominent one is the median ocellus; the other two are much harder to see, but if you look up and to the middle at about 45° from the base of the antennae you should be able to make them out: According to Tillyard again, the median ocellus used to be a pair of ocelli that have merged. Recall that the purpose of ocelli seems to be to detect light levels, rather than shapes or movement, while the ommatidia (facets) of the compound eye combine to form images of shapes as far away as 2 meters, while they can detect motion up to 20 m (or more) away. Just as a reminder, the ocelli of other insect species are often relatively easy to make out, provided you're brave enough to get close enough to make them out:
fly, that is. This morning when Eric and I went outside to plant some basil (yes, November is the start of herb-growing season here in south Florida), we noticed a dragonfly on the wall of the house that wasn't moving very much. One of its wings was at an odd angle:
For those who know a few dead languages, it probably comes as no surprise that dragonflies have excellent vision. The very word dragon (via Latin draco, from the Greek δρακοιν) means "to see clearly." And, as the late Philip Corbet noted in his magnum opus, "no other insects have compound eyes that are larger or contain more ommatidia [facets]. ... The visual field of the adult is almost 360°: the dragonfly can see in all directions except directly behind the head, where the wings and body interrupt vision—a fact quickly learned by successful dragonfly collectors." Here is a photo of the dragonfly eye: by Slovakian photographer Dusan Beno: Compound eyes are made up of thousands of repeating units called ommatidia, and, at least as found in insect eyes, the word is almost always plural. It would be pretty hard to have a compound eye with just one ommatidium! [That would be an ocellus, although ocelli are also always plural. The three dots (two blue, one black) on the forehead of that amazing close-up of the damselfly are the three ocelli, or simple eyes, that are found on all odonates.] The diminutive form of the Greek word omma ("eye") is ommatidium, and that's what 19th-century anatomists latched onto when they were deciding what to call these amazing sensory organs found in the highly visual insects (Odonata, Hymenoptera, and a few other orders). Each ommatidium consists of a lens, a cone, visual cells, and pigment cells. The composite image provided by all of these individual lenses is a mosaic; as with the half-tones of photographic reproduction, the finer the mosaic, the clearer the image. The two different types of eye found in odonates have, as you might suspect, two different functions. The ocelli excel as "light meters," while the ommatidia function, in their thousands, as form and motion receptors. The more of them an insect has, the more acute their vision is. More on this in a later post. References Corbet, P. 1999. Dragonflies: Behavior and Ecology of Odonata. Ithaca: Cornell UPBelow is my version, of a very cooperative Blue Dasher in the backyard:
If you are At All into dragonflies, you should check out the 3D image library at odonatacentral.org. Absolutely amazing. I became a member several years ago and have checked in from time to time since then. I plan on visiting more frequently now.
A couple of years ago I was going through my photo files and ran across a picture of a pretty dragonfly, Anax junius, the common green darner. I had seen this darner on the trail at Fern Forest, and since I was posting about dragonflies at the time, I wrote a brief piece about it. But I prefer to post articles about the species I can see in my own back yard; if I have to travel, even if it's just to a nearby nature center, it doesn't feel like it's as legitimate, somehow. But now I can write about A. junius to my heart's content, because I found one hanging out (literally; most members of the Aeshnidae [darner] family don't perch horizontally like other dragonflies, but hang vertically from their perches) in my Hamelia patens. I found this guy by accident; I was actually trying to track down a tiny wasp, Pimpla marginella, to provide a better image than the only ones I've managed so far, and, although it's another story, I encountered some (slight) success. As usual, the action happened between the two firebush shrubs I have side by side in a corner of the back yard. I had just finished taking the nearly successful shot of P. marginella on one of the shrubs when the tiny wasp flew away (as it does all too frequently, and always too soon!). When I turned around, I was startled to find this large, colorful dragonfly hanging vertically from a perch in the other bush, completely motionless and only about a foot away from me: separate dragonfly species into two broad groups based on how they regulate their body temperatures: perchers, which spend more time perching than they do flying, and hence gain their heat from basking in the sun, and fliers, which, one would assume, spend more time flying than they do perching, and use the heat they generate in flight to warm their bodies. (Corbet 1962, 126, appears to be the first description of this dichotomy.) Aeshnids, that is, darners, are fliers. (The distinction makes sense if you watch the perching behavior of the dragonfly in question: perchers hold their bodies out horizontally, so they're ready to fly at a moment's notice. But fliers hang vertically, which probably entails a bit more investment in the getting-into-flight process. Hence, they prefer to fly when they're active, and "perch" when they're not.) Now, normally fliers are, shall we say, flighty creatures; I'm constantly frustrated by their refusal to allow close approach with my camera gear. In fact, that same day I had to resort to digiscoping a Tramea carolina (a so-called perching species) because I wasn't able to approach it closely enough by any other means. But that, too, is another story. Today's story is about more than just a photo shoot of this most obliging individual, although it's that as well. I also wanted to find out more about this species, since it's such a striking one, and since it did me the favor of allowing me to stay so close to it for such a long time. Here's a close-up of the thorax, which contains the powerful flight muscles that propel this species through the air (at least when it's not catatonic on my firebush!). You can also see the greatly enlarged first two abdominal segments (S1 and S2, the blue ones), and the constriction, or narrowing, behind S3 that is distinctive of most aeshnids:
A large species, with green thorax and bluish abdomen. . . . Frons above with a rounded black or brown spot surrounded anteriorly by a yellow and then a blue semicircle. . . Abdominal segments 1 and 2 greatly swollen, their diameter being two or three times that of following segments.The description of the yellow and blue semicircles on the frons is a bit technical; field guide authors (Paulson 2011) tend to be more succinct, calling it a "bullseye." You can see it fairly well in the photo above that last quote. And here it is in side view: This dragonfly changes color according to the temperature; the male abdominal segments are typically blue, but when it's cool out, they appear purple instead. The physiological mechanism that allows this is quite interesting, but beyond the scope of this simple blog. In our area, this is a permanent resident, but in Canada, according to Corbet, writing in the 1950s, it appeared that the entire population is composed of migratory individuals; he concluded that their offspring,which emerge in August and September, all fly south shortly after emergence (Corbet 193). Later writers have discovered that there are actually two groups of darner larvae in ponds in southern Canada; some are resident, while others are indeed migratory:
One group develops slowly, taking nearly a year to emerge as adults in the latter part of June or the first part of July. These adults remain in the vicinity and lay their eggs in late July and early August. The second group of larvae only requires three months to develop, from June to September. On emergence, the adults take wing and migrate from the area. Their offspring develop in a more southerly location, then begin to return the following year and start the cycle again. (Mitchell & Lasswell 2005)The etymology of this taxon is elusive; according to the official list prepared by Dunkle and Paulson, the two deans of North American odonata (after Corbet), the derivation of the scientific name is unknown, while the common name refers to its "abundance and green thorax." As I speculated in my post a couple of years ago, Anax means king, lord, chief, master in Greek, while junius is a bit less certain, but could very well be a straightforward nominative form of Iunius, which is Latin for June. That would make this species' taxonomic name translate as "Lord of June," which isn't all that far-fetched. (Except that, if you check the bugguide data page for this insect, it's absent from Florida in June and July!) References Corbet, P. S. (1962). A Biology of Dragonflies. Chicago: Quadrangle. Corbet, P. S. (1999). Dragonflies: Behavior and Ecology of Odonata. Ithaca: Cornell UP. Heinrich, B., and T. M. Casey (1978). Heat transfer in dragonflies: 'fliers' and 'perchers'. J. exp. Bio. 74, 17-36. Mitchell, F. L., and J. L. Lasswell. (2005). A Dazzle of Dragonflies. College Station, TX: Texas A&M U P. Needham, J. G., and M. J. Westfall. (1955). A Manual of the Dragonflies of North America (Anisoptera). Berkeley: U of California P. Paulson, D. R. (2011). Dragonflies and Damselflies of the East. Princeton UP. Paulson, D. R. & S. W. Dunkle. (2009). A Checklist of North American Odonata, Including English Name, Etymology, Type Locality, and Distribution. Originally published as Occasional Paper No. 56, Slater Museum of Natural History, University of Puget Sound, June 1999.
Last week I noticed a couple more damselflies; these guys were in the front yard instead of the back yard. The first two pictures are from Saturday August 20th: Everglades Sprite.]
This month the odonata population (dragonflies, anisoptera, and damselflies, zygoptera) seems to have exploded in Palm Beach County. We've had dozens of dragonflies patrolling our pool, (tonight it even looked like a few of them were trying, in a not very evolutionarily adaptive way, to lay eggs in it!). But we've also had a few of their daintier cousins, the damselflies, disporting themselves quite shamelessly. Here are a few snapshots of the damselflies. These Common Spreadwings were enjoying the foliage around our pool while their larger cousins, the dragonflies, were patrolling the airspace above the water (they were a bit shy, and the closest camera to hand was the one with the "normal," not telephoto, lens, so this was the best pic I got):