October is a month of transition here in south Florida. The wet days of the rainy season start to taper off, giving way to the first few cooling breaths of our short-lived autumn, eventually to be followed by the drier and steadier days of our wintertime dry season (which usually arrives around November). That doesn't mean it won't rain; we still get appreciable rainfall in this last month of the wet season, but the rains are punctuated by spells of drier, cooler weather, that is much welcomed after the long, hot days of summer.
The first few days this month were typical late summer/early fall, with warm, humid weather. The only thing atypical about it was the lack of easterly breeze, at least in the early hours, making photography relatively easy. On the first weekend of the month, a cool front blew through, lowering the 8 a.m. temps from the high 70s/low 80s to the mid-60s. Yay! It also made photography even easier, pushing the energy budget of the insects down a mite. Whether for that reason or some seasonal effect (late emergence, early migration, what have you), I was able to add a Green Darner (only seen once before in the four years we've been on this site) and the two bee species only after the cool front. Whether they were here and I just missed them before the shift in the weather, I don't know.
These questions mean it's time to get outside on a bit more regular basis, to attempt to answer them! This year I was particularly motivated to get outside in October, because I recently joined the North American Butterfly Association, after years of telling myself "I really should join NABA." They're a nonprofit organization dedicated to education, conservation, and scientific research on—you guessed it!—butterflies! They have a butterfly garden certification program that allows you to send them a brief inventory of the nectar plants (flowers) and larval host plants (caterpillar food) in your yard, along with a check or other payment, and get a lovely sign to post in your yard:
While the certification process is not onerous (seriously—all I had to do was indicate the size of the plot, the management practices, and list three nectar plants and three host plants, no pictures, no records, nothing), it did get me to thinking about taking inventory in the yard in a new way.
So that's what I did. First, I made a table of all the butterfly plants in my yard (nearly 30 different species!). That done, I decided I needed to do a bit more. So I started another spreadsheet (oh, the joy!) to record my wildlife sightings on a monthly basis. It's a bit like the yard list that birders do, but like a true geek, I decided that it needed to be a bit more comprehensive, including month and year, rather than just as a checkmark on a bare list.
I went as far back as 2012 in my photo archives to populate the list with a bit of scattershot historical data, but going forward I'll be updating it as often as I can, and as often as I can get decent pictures. Right now it lists only a couple of insect orders: Odonata (damsel- and dragonflies) and Lepidoptera (butterflies, moths, skippers). As and when I find time I'll update the lists, at least to include the Hymenoptera (ants, bees, wasps).
This gives me an incentive to get out and see what's new, who's more abundant now, who's absent. And I will no longer have to rely solely on my wretched memory to know when certain species are present or absent, and with what kind of frequency.
As advertised, the first few mornings of October 2014 were lovely—good light, very little wind, not yet hotter than blazes. Over those first few days I've documented the following insects and spiders in the garden:
- 3 species of damselfly (the usual suspects: two fork tails [Ischnuras ramburii and hastata] and our ever-present Everglades Sprite [Nehalennia pallidula]); here's a picture of the Rambur's Forktail from September, but they look the same in October:
- 6 species of dragonfly (Band-winged Dragonlet, Little Blue Dragonlet, Blue Dasher, Carolina Saddlebags, Halloween Pennant, and a new one for the yard, Eastern Amberwing!)
- The usual species of butterfly (Zebra Heliconian, Gulf Fritillary, Cassius Blue, Cloudless Sulphur, Giant Swallowtail). Thanks to the cooler weather I was able to get up close and personal with a Cloudless Sulphur butterfly (Phoebis sennae), normally far too swift and fluttery for me to capture on "film." Yay, cooler weather!
- An Ichneumon wasp, genus Anomalon
- The usual quartet of large south Florida garden spiders (Gasteracantha cancriformis, Argiope argentata, A. trifasciata, and Leucauge argyra). Pictured is the very common (elsewhere, rare-ish in my yard) Banded Garden Spider, Argiope trifasciata. The smaller spider on the opposite side of the web from the large female is the small male. He no dummy!
- Several syrphid flies (also known as "hoverfly" or "flower fly"): Toxomerus marginatus and T. boscii.
- A pair of unidentified sarcophagid flies (also called "flesh flies")
- A "leaf beetle," Chalepus sanguinicollis:
- One of our two yard-normal halictids (sweat bees), Halictus poeyi
- A leaf-cutter (megachilid) bee, Megachile petulans, demonstrating a very stout abdomen and a tiny waist more reminiscent of a wasp than a bee—looks a bit like a little grenade or something! It also has a very loud buzz; much more noticeable than the sweat bees or honeybees that cruise through here most of the time:
The "face" of the dragonfly, starting from the very bottom, consists of mandibles (not labeled, barely visible as dark smudges at bottom) that are usually concealed under the labrum, or "lower lip" (labeled). The clypeus is composed of the "top lip," or postclypeus, and the anteclypeus, which is in what would be the "tongue" position were this a human face. Above the clypeus is the frons, from which arises the vertex, which serves as the anchor for the three ocelli, or simple eyes. The antennas arise from the base of the vertex as well. At the top of the "face,"the two eyes meet; the "joint" or seam is called the occiput. Now that we've got the unfamiliar parts of the dragonfly face out of the way, let's go back to that most familiar, and most prominent, feature of the dragonfly head: the huge compound eyes, with thousands upon thousands of ommatidia, or facets, that make up this complex visual apparatus. If you look closely, you'll see that the larger facets are all on the top of the eye, the part that's colored deep red. The smaller facets are on the bottom half, the part that's colored blue-gray and has the black "pseudopupils." Most dragonflies that you're likely to see fly during the day (the twilight-flying dragonflies are quite a bit less common in most people's experience) and have excellent color vision. Our own eyes have three different color-sensitive retinal proteins, called opsins, that give us the familiar red-green-blue mix of color perception. (Those RGB color values don't correspond exactly to the peak sensitivity of each opsin, but, meh... close enough). Diurnal (day-flying) dragonflies, on the other hand, have as many as five opsins in their visual reception apparatus, giving them access to a much greater range of the electromagnetic spectrum. What's interesting is the arrangement of the ommatidia with respect to the part of the spectrum they're sensitive to. Recall the visual spectrum mnemonic: ROYGBV. That is, red-orange-yellow-green-blue, in ascending wavelength order. Red has the longest wavelength, while blue, violet, and, beyond the violet, ultra-violet, have the shortest wavelengths: Those larger facets on the top of the dragonfly's eye? They are sensitive to UV light and blue light (on the right in the image above). The smaller ommatidia on the bottom half of the eye? They're specialized for longer-wavelength light, like orange or green. As anyone who's tried to get close to a dragonfly, whether to capture it or just its image, those eyes are extraordinarily capable of detecting movement. That great visual acuity appears to be related to the presence (and direction) of the pseudopupil (the dark region in the light blue-gray portion of the eye in the photo above). They seem to indicate the insect's fovea, or zone of greatest visual acuity. Land and Nilsson (2012) write that "perhaps the most useful feature of the pseudopupil [to the entomologist, if not to the insect itself] is that one can use it to measure inter-ommatidial angles. If one rotates an insect's head through a degrees, and the pseudopupil appears to move across b facets, then the inter-ommatidial angle is a/b degrees. Variations in inter-ommatidial angle in different planes, and in different regions of the eye, can be mapped in this way, revealing how the eye is is organized to make the most of its limited visual acuity." Mapping the organization of the dragonfly eye is exactly what Truman Sherk did in a classic series of articles in the mid-1970s, tracing the development of dragonfly eyes from larva through adult animal, mapping the foveae and relating it to predation style. In the photo above you can see the pseudopupil looking directly at the camera, "anteriorly" as the scientists like to say. That is, directly in front of the animal. In the example below, though, you can see lots of "accessory" pseudopupils: That is, in addition to the main, large pseudopupil, you can see several other dark spots; each of these is also a pseudopupil and indicates a zone of great visual acuity. According to Sherk, "the size and shape of the accessory pseudopupils [appear] to be related to the geometrical arrangement of the corneal facets, the slight curvature of the individual facets, and to the regional radius of curvature of the cornea. The contrast between the accessory pseudopupils and the surface [appears] to be related to the maturity of the cells between the cornea and the rhabdom." That might be a bit more than you wanted to know about the dragonfly and its face, but next time you see a dragonfly buzzing off when you so much as twitch a muscle in its direction, you might have a deeper appreciation for what makes that response possible: those amazing eyes. References Corbet, P. (1999). Dragonflies: Behavior and Ecology of Odonata. Ithaca: Cornell UP Land, M. F., and D.-E. Nilsson. (2012). Animal Eyes, 2d ed. New York: Oxford UP. 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, NJ: Princeton UP. Sherk, T. E. (1978). Development of the compound eyes of dragonflies (Odonata). III. Adult compound eyes. J. Exp.Zool 203:61-80.
The darners are long and slender-bodied, like a darning needle, and they include the largest Florida Dragonflies. Their eyes are very large and meet in a seam on top of the head. In most species scars can be seen on the eyes of a female where a male has held her during mating. Females have an ovipositor with blades, as in the Petaltails. Darners hang vertically on a perch whether it is a vertical stem or a horizontal twig [or in this case a brick-face wall]" (20).Unfortunately I wasn't aware of the importance of the thorax in distinguishing among several possible species in different genera, Comet Darner (Anax longipes), Cyrano Darner (Nasiaeschna pentacantha), and Regal Darner (Coryphaeschna ingens), but I'm pretty sure that this is the latter species. [UPDATE 9/10/10: Upon further review, it looks like Twilight Darner (Gynacantha nervosa) is a better match for this individual. The thoracic markings are indistinct, which fits G. nervosa much better than C. ingens.] In the first place, the friendly folks at bugguide.net think it's likely to be. In the second place, most of the photos I've seen of Comet Darners show "blotches" on the abdomen, rather than the "dots" I see on this one. Cyrano darner has those dots, but, according to the checklist from Odonata Central, has not been recorded in Palm Beach County, while Regal Darner has been. (Not that going by the book is a sure guide, particularly with a tropical storm that could be blowing things in from far away, but it's another piece of the puzzle.) Now, two years later, I sure wish I'd taken more photos, but at the time I was more concerned with putting the hurricane shutters on than I was with narrowing down the ID of the animal. I was pretty sure the photos I had would be conclusive. As it turns out, they are simply not good, from any angle, because I didn't know what I should have been looking for. That's why relying on photography for a positive ID is a problem: if the field mark you need is not in focus, you're out of luck. (On the flip side, it's a good learning tool: now I know to try to get good pictures of the thorax for any darner, so we can use the markings there to help figure out what it might be.) Here's the other side, of the animal, with a better view of the tail: like this one, you can see that they are quite long; the ones on this lady are pretty short. No, the ovipositor is a bit higher up, on the right of the picture (ventral, or bottom, side of the abdomen). [UPDATE 9/10/10: the ovipositor is above the last abdominal segment, 10; on that segment (S10), you can see, in Dunkle's words and in that photo of the tail, "2 spines on the underside...which are used during egg deposition. [They] form a fulcrum when she uses her ovipositor blades to lay eggs in soil" (28).] So don't get confused if you see a male dragonfly with terminal appendages. That's perfectly normal. A male dragonfly with an ovipositor, though—that would be big news. So, to make a long story short, if you want to take better nature photos, learn more about your subjects, so you can know what it is you're trying to capture. Then see if there's a way to make it pretty. I have a long way to go on both fronts... But it's a fun road to travel!