I haven't seen nearly as many dragonflies in the back yard this summer as I have in years past; I'm not sure why. But it seems that nowadays I have to travel if I'm to see anything like the diversity or abundance of species I'd enjoyed in my back yard for the four years we've been in the new place. So the Saturday morning of Labor Day weekend I went to Yamato Scrub, camera in hand, hoping to score an odonate fix. I managed to find quite a few, as well as some lovely little butterflies. As usual, I saw many more than the few who cooperated for the camera. Here are two, one each from the dragonfly and damselfly groups. First, the lovely red dragonfly Tramea onusta, called the Red Saddlebags (there is a Carolina Saddlebags as well; almost indistinguishable except that the black spots on the tail in Red are only on top, whereas in Carolina, the black goes all the way down the sides):And here's a damselfly. This one's a bluet, I suspect Atlantic (Enallagma doubledayi), but I can't rule out Familiar (E. civile) without having the specimen in hand and an argument with specialists: I think the broad bar of blue connecting the "eyespots" (called postocular spots by specialists) on the back of the head argues strongly in favor of Atlantic over Familiar, but it's by no means conclusive. Here's the bit I'm talking about: According to Paulson, who wrote the book on these bad boys, "postocular spots larger in Familiar and without occipital bar, but overlap." Bonus picture: Ceraunus blue butterfly, Hemiargus ceraunus: I love how the blue in the tailspot lights up so brilliantly in the right light. References Paulson, D. R. 2011. Damselflies and Dragonflies of the East. Princeton: Princeton UP.
...said the spider to the lady beetle. And yet, nothing happened. This morning before work I went out and, as usual, was taking pictures of whatever I could find in the yard. I found this lovely Southern Sprite damselfly (first of the season): Gasteracantha cancriformis, commonly known in south Florida as a "crab spider," although most naturalists call it the spiny-backed orbweaver to avoid confusing it with the "true" crab spiders like the one above). The true crab spiders are so called because their front pairs of legs are drastically elongated, much like the pincers of a crab. It's one of the largest spider families, with over 2,000 species worldwide. There are at least 130 species in 9 genera in the United States, so identification to species level is left to the true spider experts, the araneologists (as distinct from the arachnidologists, who study arachnids in general, which includes arthropods from other orders such as scorpions, mites, ticks, and chiggers, in addition to the Daddy Longlegs, which aren't true spiders at all). While I was taking pictures of this unusual flower-trapping arrangement (normally I see the petals of the flowers curled down, rather than up), I noticed a wee little lady beetle about to become breakfast: And then the strangest thing happened: the spider just remained motionless while the beetle climbed on the spider's back, tumbled off onto the disk portion of the flower, and then scurried away out of sight! I wasn't able to snap a picture of the scene as the beetle left, but I was certainly surprised to see what I assumed would be a typical predation scenario turn into nothing at all. In case you're curious, the lady beetle looks very much like the "metallic blue" lady beetle, Curinus coeruleus, although it's by far the smallest one of them I've ever seen. References Marshall, S., & G.B. Edwards. 2008. Florida’s Fabulous Spiders, 4th ed. Hawaiian Gardens, CA: World Publications. Ubick, D., P. Paquin, P. E. Cushing, & V. Roth (eds.). 2005. Spiders of North America: An Identification Manual. Keene, NH: American Arachnological Society.It's always a pleasure to see these relatively rare damselflies. (Odd, too, how abundance is so tied to locale: Everglades Spite (N. pallidula) is considered very rare, while Southern Sprite isn't, and yet I get dozens and dozens of the former over several months and very very few of the latter. I guess being near the Everglades is conducive to the occurrence of Everglades Sprite? While most people across the range of these insects are not near the glades...) When I was finished with the sprite's photo session I wandered over to the patch of dune sunflower I have growing along the drive. I noticed one flower had two petals sort of curved upward toward each other, indicating, most likely, the presence of a hunting spider. (That is, a spider that hunts without using a web.) It had tied the petals together with a strand of silk; you can see them curling up toward the camera in the photo below: Thomisid spiders are commonly known as "crab spiders" (not to be confused with
Over the weekend I spent a lot of time in the "field," a fancy name for my small suburban backyard (I say suburban because here in Boca Raton, even with city hall only three blocks away, there is no "urban" to speak of). This was the first weekend after A Lot Of Rain, so there were lots and lots of damselflies to sort through. Dozens of Everglades Sprites (Nehalennia pallidula), several Rambur's Forktails (Ischnura ramburii), a few Fragile Forktails (Ischnura posita), one or two Citrine Forktails (Ischnura hastata), and, for the first time that I'm aware of, Southern Sprite (Nehalennia integricollis). (A bit later this week I saw a sixth species, Carolina Spreadwing [Lestes vidua]. Yay! But I discovered that they're MUCH more wary than all other damselfly species combined. Boo!) As a rule, damselflies are quite a bit less conspicuous than their larger cousins, the dragonflies. Their bodies are slimmer, they tend to hold their smaller wings parallel to their bodies over their backs, rather than perpendicular to their bodies like those great big oars of wings on the dragonflies. They like to flit around in the tall grasses or, if you're one of those more meticulous lawnkeepers, any shrubby vegetation you might have (although, if you're a meticulous lawnkeeper, you or your gardener probably use pesticides, so you're much less likely to see any of these beautiful little mosquito-eaters than those of us who practice a more holistic gardening approach, sometimes referred to as "leaving things alone."). The sprite family of damselfly takes this inconspicuousness to the extreme. Hal White, the longtime odonate observer up in the Delmarva peninsula, writes about these little guys as follows:
Because it is inconspicuous and rarely flies unless disturbed, it is easy to overlook even when searching for it. The presence of one Cyrano Darner at a pond attracts attention while hundreds, or even thousands, of Southern Sprites might be at the same location and go unnoticed.I doubt that there are hundreds, or even dozens, of Southern Sprites in my little quarter acre, but I can certainly say that there's at least one. And it's very nice to meet her at long last: They have the prettiest blue eyes, and a wonderful metallic green color that looks a bit dull in the shade but really lights up when the sun hits it: Etymology Nehalennia, as I've discussed before, is a river goddess from the Rhine region; the specific name integricollis means that the hind lobe of her prothorax (her collar, if you prefer), where the male damselfly would grasp her for copulation, is "entire," or complete (integral), rather than interrupted or grooved. Presumably the shape of this region of the thorax matches the terminal abdominal appendages of the male to facilitate reproduction, as illustrated by this pair of Everglades Sprites: According to Westfall and May, the Southern Sprite is the "smallest, most southern, and least studied of the darker, northern group [there are five species in the genus Nehalennia, and three of them comprise the "northern" group of metallic green damselflies, while the remaining two are part of the "southern" group of darker, browner damselflies]. It is found in areas as diverse as the margins of sandhill lakes in Florida and sphagnum bogs...in New Jersey, but its ecological requirements have evidently never been described in detail." Giff Beaton observes that this species "tends to stay in heaviest vegetation, and small size makes observation difficult unless focusing on a small area and looking for movement." I can certainly attest to that. I've been playing hide-and-seek with one or two of these little ladies for days now. Just when I think I'm about to get a good photo, she takes off, and when I finally relocate "her," I find one of the dozens of Everglades Sprites that are littering my lawn, and she's nowhere to be found. So, while we don't know too much about this lovely little lady, we do know that she's alive and well in downtown Boca, and perhaps at a natural area near you! References Beaton, G. (2007). Dragonflies and Damselflies of Georgia and the Southeast. Athens: U of Georgia P. Westfall, M. J., and M. May. (2006). Damseflies of North America, Revised Edition. Gainesville: Scientific. White, H. (2011). Natural History of Delmarva Dragonflies and Damselflies: Essays of a lifelong observer. U of Delaware P.
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!
The Monday after Thanksgiving is a great time to get out to a nearby natural area. While most folks are back at work after a four-day weekend, those of us who have the foresight to request this day off get to experience something fairly rare around this time of year: solitude! The prospect of some alone time, combined with the knowledge that two of Palm Beach County's best birders had reported a juvenile Red-headed Woodpecker at a location near me decided my destination on this fifth day of a four-day weekend: Pondhawk Natural Area, which, as loyal readers of this blog know, was formally opened just a couple of months ago. And on this day, as expected, I had the place all to myself! I started out on the concrete walking trail, chasing warblers and other birds as the fancy struck me, and I wound up assembling a fairly respectable list without even trying very hard—28 species, including House Wren, American Kestrel, Osprey, Red-shouldered Hawk, and the target bird: Red-headed Woodpecker. But that wasn't the only, or even the primary, goal of the excursion. I just needed to get back out into one of the prettiest natural areas in Boca Raton. It's a very pretty park, with 5 different ecological communities (you can't really call these tiny snippets of area "ecosystems")—scrub, scrubby flatwoods, mesic flatwoods, hydric hammock, and sawgrass slough. I spent most of my time on that concrete trail, which winds through the mesic and scubby flatwoods (yellow and green areas in the map below) that surround the pond (the orange hydric hammock in the map), but I also took an excursion onto the sandy trail that leads through the southwestern portion of the site (also mesic and scrubby flatwoods). I never did get onto the trail through the scrub proper. Both scrubby flatwoods and "true" scrub are dominated by shrubby, scrubby plants that don't need a whole lot of water: sand live oak, saw palmetto, prickly pear cactus, etc. Where there are "woods" around (hence scrubby flatwoods), they are usually sand pine or, in slightly wetter scrubs (mesic, halfway between dry [xeric] and wet [hydric] sites), slash pine. The flatwoods areas at Pondhawk have numerous snags (dead trees left standing in the wake of a wildfire on this part of the site back in 2010) and living slash pine trees, providing excellent foraging and even nesting habitat for woodpeckers like the red-bellied (common in Palm Beach County) and red-headed (much rarer in Palm Beach County):
Everyone's still a bit confused about what this bird is doing here, so far south of its known nesting sites in the county. Red-headeds are slightly migratory, in that they move locally in winter to exploit better resources than they can find near their nesting sites, but only if their nesting sites are deficient in some food resource. Up north, a poor mast crop (acorns) is what triggers this migratory response; down here, with seemingly abundant year-round resources, it's a bit of a mystery why this juvenile bird would wander like this. Eventually the woodpecker got tired of me chasing it from snag to snag, and decided to fly right over my head (too quickly for me to get a picture, drat it) and back up to a site far enough away that it wasn't worth hiking over to, so I continued on my way and left him (or her) in peace. On the way out I got a couple of other decent shots, like this Red-shouldered Hawk perched on a tree overlooking the pond, thus doing its best to look like the avian version of the "pondhawk" for which the site is named:
Interestingly, they close their wings over their backs, and drop their bodies to parallel their perch, when a dragonfly flies near. Pairs in tandem do this also, but the approach of a human does not elicit this behavior.Now, there were plenty of dragonflies flitting about, so I can't exclude the possibility of this damselfly doing this in response to them rather than to me, but on both perches that I chased this little lady to, she closed her wings over her back in what I thought was a response to my approach:
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:
After my post a couple of weeks ago where I lost track of a pair of damselflies in tandem before I found out whether they actually attained the wheel position I've been hoping for another chance. Today, the first sunny day after what seems like a week of rain, I got my wish. In spades! This evening there were more Nehalennia pallidula than I could shake a stick at! Everywhere I looked was a male looking for a mate, a pair that I accidentally separated with my clumsy walking through the tall grass, or a pair actually mating! I managed to latch onto one pair that seemed to know which end was up, and I was able to follow them without scaring them to separate. I even managed a few "in-process" pictures. Here is one of the puzzles from last time; I simply couldn't figure out how the male grabs onto the female and THEN transfers the sperm from his primary genitalia at the tip of the abdomen to his secondary genitalia on segment two. Well, here is how he does it: may not be abundant in the wild*, but in the urban wilderness of my property, I would guesstimate, just ticking them off on my fingers, that there were at least two dozen individuals today: 8 in the tall grass behind the shed, 5 or 6 more under the canoe, at least 6 more in the front yard, and probably 10 more on the other side. These are conservative guesstimates. These numbers are just for the Everglades Sprite; I didn't even mention (until now) the Fragile Forktail or two that I saw, or the Rambur's Forktail pair I saw mating earlier today. Don't know where all the Citrine Forktails have gone (a month ago they were present in numbers similar to those of the Everglades Sprite today), but their position in the ecosystem has not gone unfilled! Spring may be almost over, but it sure is still la saison d'amour here in my yard! Go odonata! *I know no one ever clicks links anymore, so I'll just tell you that its status is "Near Threatened" on the IUCN Red List for 2011.2.
The last few days have seen the finest weather I can recall since moving to Florida. Daytime highs in the low- to mid-70s, overnight lows in the 50s and 60s, a light breeze making sure that even when you're out in the sun you feel cool and refreshed. This is what living in south Florida is supposed to be like! When the weather's this nice, one of my favorite things to do during my lunch break is go out and get dirty. And every now and then, getting dirty involves rolling around in the grass chasing after lovely little damsels. And every now and then, when you chase lovely little damsels you catch them. Here are some pictures of the lovely little damsels I caught during my lunch break one day this week. A beautiful, if somewhat immature, female Citrine Forktail (Ischnura hastata):
Some insects feed on rosebuds, And others feed on carrion. Between them they devour the earth. Bugs are totalitarian.
—Ogden Nashmy yard has been veritably plagued by them for weeks now (if you can call the presence of beautiful little insectivorous fliers a plague). Just to show how many there were, here are a male and immature female jockeying for space on the same wildflower/weed in my front yard: One study of just one type of parasite (gregarines, one-celled protozoans) demonstrated that these organisms tend to be host-specific as well, so when you add up the number of kinds of parasites, then multiply by the number of known species of hosts, you're dealing with astronomical quantities.) The female of Rambur's Forktail is polymorphic, which means that she comes in more than one color form (but only one per customer, please). The individual pictured has what is known as andromorph coloration (from Greek andro-, "male"); that is, her color is almost exactly like that of the male. Her thorax, though, unlike the green thorax of the male, is blue. This color difference means that she is technically immature; if she were older, it would be green just like the male's. How can I prove that she's female? Well, today it was pretty easy: she's the one on the bottom in the wheel, or heart, position:
Male Odonata are unique among exopterygote insects [ie, those that undergo incomplete metamorphosis, with only egg-larva-adult stages of life, rather than complete metamorphosis, egg-larva-pupa-adult] in having the primary genital orifice and the intromittent organ located at opposite ends of the abdomen. (Corbet 1999)During copulation, the female's tail tip is pressed up against a secondary genital structure located between the male's second and third abdominal segments. That structure, called the seminal vesicle, has been packed with sperm from abdominal segment 9, right near his own tail tip—how he manages to first clasp the female and then transfer the sperm would be a complete mystery to me were it not for the helpful illustration from Corbet that I reproduce below—and is being pressed up against the female's tail tip so the sperm can be transferred from said vesicle to her spermatheca; any eggs that pass through that spermatheca then become fertilized. Here is a graphic representation of the process from the dean of odonate studies, Philip Corbet (you have to click the image to see all 8 stages; the thumbnail cuts the picture off mercilessly):