Posts Tagged 'dragonflies'

BioBlitz Notes

Birds are hard to capture with phone cameras, the standard way people enter information on iNaturalist. I led two bird groups of Macualay Honors College students on the BioBlitz Saturday. This is the only picture of a bird I put into iNaturalist. We tallied birds seen the old fashioned way, with paper and pencil.

Macaulay the honors program at CUNY. They do a BioBlitz every year for their sophomores. This started in 2012 when the in-coming dean, a primatologist, was dismayed to see the one science course sparsely attended. A BioBlitz is a survey of lifeforms over a specific time-span. Every year the blitz has been in a different location in the city. Up to five hundred students take part. The data they help collect is used throughout the year in their classes. Here’s what we found.

This year they divided the blitz between Green-Wood and the Gowanus Canal area. In one of these things, volunteers, or in this case students, accompany educators, naturalists, etc., to search and record. You’ve seen some of the moths I photographed during the night component; there was another moth unit and a bat team that night as well.

The students were not particularly familiar with the common birds, although they all knew what a pigeon was. We had good views of a Great Blue Heron and Red-tailed Hawks, both the perching one pictured and another flying a few minutes earlier. There were lots of warblers out and about, especially American Redstarts. A northeast wind bought a fallout of migrants to town. Following these through binoculars takes some practice. The sight of a Belted Kingfisher bought a real smile of joy to the face of one young woman, an Indian-American — a dozen species of kingfishers are found in India.

My 3pm group was a quartet of the most insect-phobic humans I’ve ever seen. They were terrified of flying things, doused themselves in citronella, and one even jumped away when I pulled a cicada exuvia off a tree. It wasn’t a surprise: knowing how jumpy they were, I announced that it was coming — a hollowed out exoskeleton, lifeless, harmless — but no matter. (I was nervous around bees until after graduate school, so there is hope.)
While looking for birds, the motion of large dragonfly can easily catch the eye. This looks like a Shadow Darner, a species I’ve never seen in Brooklyn before.
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On the absolute necessity of cities for biodiversity.

Paulson on the Odonata


Dennis Paulson’s new Dragonflies and Damselflies: A Natural History‘s is a great introduction to odonating.

Paulson has written the standard field guides to American/Canadian odes as well as dozens of journal papers on odonates. The pictures in his field guides are too small; that’s these guide’ principal fault. But consider: there are 461 species to be covered in the US and Canada. There is strong sexual dimorphism in odonates, meaning at least two images for each species. Some damselfly species have four or five color forms. Dragonflies and Damselflies of the East is 519 pages long, not including glossary and index. Gotta be some hard calls for the author and publisher in this field of field guide publishing.

This new book, however, is coffee table format. It’s aimed for a popular readership. While there is a Further Resources appendix, I note the absence of a real bibliography. There’s a lot of scientific literature out there; touching base with it would have been a good thing, especially with our unparallelled ability to pull up scientific literature on the ‘net (if not full text than at least the abstract).

Chapters on natural history alternate with two-page spreads on individual species from around the world. At the time of publication, there were 6,299 described odonate species. That number is sure to change. Nearly two hundred of these were first described between 2015-2017. Only a small sample are included here, obviously, representing the great range and diversity of this order of insects.

News to me: the Common Winter Damsel (Sympecma fusca), found in southern and central Europe east to central Asia, stays dormant through the winder. They grab hold of something and sit out the winter in dormancy. The two other species in this genus are the only overwintering adult Odonates we know of. Advantage: very early start to reproduction, before predatory migratory birds show up. Disadvantage: they suffer “moderately high mortality from rodent predation” in winter. A frosted-over damselfly is still fresh meat, after all.

On the Azores, the population of Citrine Forktails (Ischnura hastata) is all female. They’re the only ode that manifests parthenogenesis. With so many species, there are many strategies and adaptations and habitats. The basic plane is the same, but the differences are what fascinates.
The Eastern Pondhawk (Erythemis simplicicollis) rates an entry because it is one of the few species in the world that seems to be increasing its numbers, going against the general decline brought about by… us. I photographed this one in Brooklyn. They thrive in any kind of fresh water; many other species have rather more specific requirements: gravel bottoms, slow moving streams, fast moving streams, muddy bottoms, etc.

What else? Much else. Up to 60% of the weight of a dragonfly is muscle used to power their four wings. “Although they operate independently, the fore- and hindwings interact with one another. The hindwings suffer slightly increased drag owing to the turbulence created in front of them by the forewings, but the positive pressure generated by the hindwings actually decreases drag on the forewings.”

There are even some numbers on flight speed: average speed of a moderate sized dragonfly: 4.5 mph. The largest dragonflies, the darners, can hit bursts of 34mph!
Sweetflag Spreadwing (Lestes forcipatus) female. Photographed in Alley Pond Park in Queens, on the same day as this
Slender Spreadwing (Lestes rectangularis). These are now the only Queens records for Lestes genus spreadwings at Odonata Central. iNaturalist has one more, seen in 2016, but nobody could get it down to species level. I have a similar problem with the third spreadwing I photographed in Ally Pond Park that day. Without the specimen in hand, identification can be impossible, but I’d rather see them flying than tucked into someone’s drawer. Brooklyn, by the way, has only one record of a spreadwing, but here too the picture is too obscure for species-level.

The Better To See You With

You may have noticed the long antennae of butterflies, or the sometimes very elaborate and feathery antenna of certain moths.
Male moths especially, like this Chickweed Geometer (Haematopis grataria), pick up the scent of female pheromones from great distances. Some beetles also have long antenna; c.f. the “long-horned beetles.”
But note how minor a dragonfly’s antenna are.
This is a Blue Dasher male. Blue Dashers are the most common dragonfly species in NYC. And yes, they definitely see you coming.
Here’s a female Great Blue Skimmer.
It’s only recently that Odonata antennae have been shown to have olfactory sensory pits on them. But a dragonfly’s main sensory receptors are its eyes. We humans, who bleat on and on how we are the top a-number-one Americans of the animal world, have three color-sensing proteins in our eyes. Dragonflies have from eleven to thirty, depending on the species (and for some, age). They see in “ultra-colour” as New Scientist puts it. There are as many as 30,000 facets on their compound eyes — along with bees, they have the largest eyes in the insect world — which can see in all directions at once.

Except obviously, their blind spot, which is behind and below. “They see the sky as a very bright background against which flying insects [their prey] stand out dramatically,” Dennis Paulson writes in his new natural history of odonates, which I will give more attention to shortly.

Robber Flies & Dragonflies

A Holcocephala genus gnat ogre. Hey, I don’t make these names up, I just report them. Like the examples below, these are robber flies. Ommatius genus. Robber flies hunt and kill “insects of many orders” according to bugguide.net. In this case, a fly victim.Genus Efferia. Another captive fly.Here, the prey looks like a tiny wasp.

And now for some dragonflies. These are Great Blue Skimmers mating.Female Great Blue Skimmer.One of the meadowhawks.Female Carolina Saddlebags.Spot-winged Glider. It’s rare to find these perched. They seem tireless when flying, patrolling meadows and lawns for prey. This is one of the migratory species: the late summer generation will head south. Like with its Pantala genus-mate, the Wandering Glider, their hindwings are wider than other species of dragonfly, better adapted for frequent flying.
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The Republican assault on America comes in many blows. Trump’s environment-rapists are attempting to undercut public control of public lands. The Forest Service wants to revise its rules to bypass environmental impact studies for the benefit of loggers and miners. They are, of course, bullshitting about the intent of their sneak attack. Comments on this proposed rule change are due by Monday.

I excerpted this from a recent comment because I thought it was so spot on: “I am opposed to the U.S. Forest Services proposal to cut out public participation from the vast majority of its decisions. I want to have the ability to comment on decisions affecting places I care about in the future. The current proposal would fundamentally change the relationship between the U.S. Forest Service and the public, cutting our voices entirely out of how to manage these special places.”

Of Wings and Stigmata

Found the remains of a dragonfly on a Brooklyn sidewalk recently. Possibly a Common Green Darner, one of our most common species. One of the hind wings was still in pretty good shape.Pretty good, but at 40X showing some wear and tear. These two shots are hand-held through the microscope, so not as great as I’d like them, but certainly passable. And the leading edge. I was surprised to see how rough it looks, with regularly spaced thorn-like structures. But I shouldn’t have been. We think of the aerodynamic as streamlined, but this is old school thinking, from the Art Deco in Space, a.k.a. Jetsons, Era. We now know, from things like bird feathers, that a rough surface actually works better for flight.

The dark yellowish bit here the pterostigma, sometimes called simply the stigma, and yes, stigmata in the plural. (See first image for location: on front edge of the upper left). This is a thickened, pigmented cell. A number of other insects have these, but they are most obvious on dragonflies, some of our biggest-winged insects. The stigmata have greater mass than similar-sized sections of the wing. They seem to be a kind of ballast, helping with flight stabilization. Odonates are extraordinary fliers. See here for more detail: “By passive, inertial, pitch angle control, the pterostigma probably makes the wing beat more efficient in slow and hovering flight of small insects, while its raising of the critical flight speeds probably is of more importance to larger insects.”

Exuviae

Wait… what? This Rambur’s Forktail damselfly is perched on the exuviae of a dragonfly.Another view of the male Rambur’s green-blue color pattern. Dragon- and damselfly eggs are laid on or near water. The larval stage is aquatic. After a season, or a year (or more depending on species and location), the aquatic nymph crawls out of the water, onto a twig, stone, etc. A floating leaf in this case. The adults emerge from these, with wings! The remaining husks of exosleton are called exuviae. These were left by dragonflies: the short wing-like gill structures on the back tell you this. This is what’s left of an aquatic damselfly. The gills are at the end of the abdomen. This is about an inch-long and quite hard to see from up above. There were a lot of dragonfly exuviae around the Sylvan Water the other day, presumably from Eastern Amberwings, which were all over the place. This was the only damselfly exuvia I found, even though there were several adult damselflies flying.And mating…

More Insects

The Common Sootywing. The Kaufman guide says “flight is slow and close to the ground” but I beg to differ with the first characterization. This was about the tenth I’ve seen in various places before I could get a photo.Black Swallowtail, another mover, if not shaker.This is a Great Blue Skimmer, another case where the description of the adult male gives us the common name. This is the female. This photo makes her look smaller than in real life. The larval Asian Ladybug (they seem to have dropped the “multicolored” in the common name; what’s distinguishing about them is that they are variably spotted in the adult form).

No photo, but on 6/2 I spotted a Two-spotted Ladybug in the same Brooklyn Bridge Park patch I first found them in in 2012. I also wrote about them for Humans & Nature.


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