Archive for the ‘education’ Category

Pop quiz answer key

June 9, 2017

Perhaps the simplest way to provide answers to the recent pop quiz — in which readers were challenged to identify the gender of two Southern Spreadwing damselflies (Lestes australis) — is to show what the teneral/immature male (shown in my last post) will look like when he’s a little older.

The following photos show Southern Spreadwings spotted at Mason Neck West Park, Fairfax County, Virginia USA. Both individuals are male, as indicated by their terminal appendages and blue coloration.

Both photographs of the male Southern Spreadwings were taken at an angle that shows their terminal appendages clearly.

All male damselflies have four terminal appendages, collectively called “claspers.” Male damselfly terminal appendages don’t look exactly the same for all species of damselflies, but their function is identical. Claspers are used to grab and hold female damselflies during mating: an upper pair of cerci (“superior appendages”) and a lower pair of paraprocts (“inferior appendages”).

In contrast, female damselflies have two cerci (sing. cercus), superior appendages that have little or no function. Notice the two “nubs” at the tip of the abdomen, as shown in the photo of the female Southern Spreadwing that was featured in the pop quiz.

Editor’s Notes: There are five families of damselflies (Suborder Zygoptera) in the United States of America, although only three families occur in the mid-Atlantic region: Family Calopterygidae (Broad-winged Damselflies)Family Coenagrionidae (Narrow-winged Damselflies); and Family Lestidae (Spreadwings).

Male Broad-winged Damselflies and Spreadwing Damselflies have terminal appendages that are large enough to see with the unaided eye. Generally speaking, both male and female Narrow-winged Damselflies are too small to see their terminal appendages clearly in most photographs.

Copyright © 2017 Walter Sanford. All rights reserved.

Pop quiz

June 7, 2017

OK, it’s time to assess what you’ve learned about damselflies by following my blog.

Two Southern Spreadwing damselflies (Lestes australis) were photographed on the same day at the same location. Both damselflies are teneral/immature, that is, they are relatively young. One is a female; one is a male. Can you identify the gender of the damselflies shown in the following photos?

I’ll give you a hint: Examine their terminal appendages by looking at the full-size version of both photos.

No. 1

No. 2

Editor’s Note: The answer key will be published in my next post.

Copyright © 2017 Walter Sanford. All rights reserved.

If snakes could talk

June 1, 2017

In my experience, snakes flick their tongue frequently when they feel threatened by a predator. If snakes could talk, then this one might be saying “You’re making me feel anxious!”

10 MAY 2017 | Fairfax County, VA | Eastern Gartersnake

An Eastern Gartersnake (Thamnophis sirtalis sirtalis) was spotted along Pope’s Head Creek at Hemlock Overlook Regional Park, Fairfax County, Virginia USA. A wider view shows the snake is approximately two (2) feet in length. Notice its tail appears to have been amputated and healed afterward.

10 MAY 2017 | Fairfax County, VA | Eastern Gartersnake

A closer look at the snake shows several fresh injuries along the body, such as the gash near its head.

10 MAY 2017 | Fairfax County, VA | Eastern Gartersnake

Several bus loads of middle school students were visiting the park on 10 May 2017. I saw three students downstream from me who were separated from the larger group. They were throwing rocks at something along the shore. As I approached them, they started walking in the opposite direction. I spotted the snake when I reached the same place where the students had been throwing rocks.

10 MAY 2017 | Fairfax County, VA | Eastern Gartersnake

I’m guessing the students were trying to kill the snake before they saw me. So if snakes could talk, then this one might be saying “Thank you for saving my life!”

10 MAY 2017 | Fairfax County, VA | Eastern Gartersnake

Editor’s Comments: What’s the take-away from this ugly experience? This is another example of “good thought, bad idea.” It was a good thought to schedule a school field trip to a nature park; it was a bad idea to lose track of several students! Middle school students require adult supervision at all times. Trust me, as a retired K-12 science teacher, this is the voice of experience talking. The teachers are lucky none of their students were injured when they were missing in action. The snake wasn’t as fortunate — it was injured as a consequence of the teachers’ negligence. Let’s hope the snake survived its injuries!

Copyright © 2017 Walter Sanford. All rights reserved.

Swift River Cruiser (emergent female)

May 30, 2017

A Swift River Cruiser dragonfly (Macromia illinoiensis) was spotted along the Potomac River at Riverbend Park, Fairfax County, Virginia USA. This individual is a late-stage emergent teneral female, as indicated by her terminal appendages.

Many of the major milestones during the miraculous process of emergence occurred before I spotted the dragonfly. I photographed the process from the first sighting to the time when I had to stop (see The Backstory, below): I shot 102 photos in approximately one hour; time is compressed by showcasing five (5) select photos from the first-to-last sighting.

The following photo is the first image from a time-series documenting the late-stage emergence of the teneral female. Elapsed time is expressed in hh:mm:ss format, e.g., 00:00:00 is the time when I spotted the emergent teneral female, and 01:01:15 is the total elapsed time.

27 MAY 2017 | 09:09:13 am EDT | Elapsed time: 00:00:00

The wings seem to be fully expanded (as shown in the preceding photo), evidenced by the fact that it appears some of the greenish hemolymph has been pumped out of the wings and into the abdomen.

27 MAY 2017 | 09:51:08 am EDT | Elapsed time: 00:41:55

Notice the wings are mostly clear in the following photo, in contrast with the first photo in this gallery. Next the abdomen expanded slowly until it was longer than the wings, as shown in the last photo.

27 MAY 2017 | 09:52:33 am EDT | Elapsed time: 00:43:20

As time passed, more of the adult coloration began to appear. Notice the large yellow spot on the dorsal side of abdominal segment seven (S7).

27 MAY 2017 | 09:57:39 am EDT | Elapsed time: 00:48:26

The last photo shows the dragonfly waiting for the wings and body to harden before its first flight.

27 MAY 2017 | 10:10:28 am EDT | Elapsed time: 01:01:15

The Backstory

I woke up at 4:30 a.m. in order to be at Riverbend Park when the gates open at 7 a.m. I had to attend a training session in order to be a volunteer collector of dragonfly exuviae for a research program sponsored by the park. The class started at 10 a.m., but I wanted to look around and shoot photos before the class.

I found almost nothing photo-worthy until soon after 9:00 a.m. when I spotted the emergent Swift River Cruiser dragonfly. The emergence was well underway at that point; I had to go to class before the wings spread and the teneral dragonfly flew away.

The emergence site was in a high-traffic location, so the daughter of a woman in the class guarded/watched the teneral until it flew away safely. After class, I collected the exuvia. I will shoot a set of studio macro photographs of the exuvia before returning the specimen to the park.

Swift River Cruiser is a new species of dragonfly for my life list.

Copyright © 2017 Walter Sanford. All rights reserved.

Cobra Clubtail external reproductive anatomy

May 28, 2017

I liked to make paper- and plastic models when I was a child. Seems like the directions for assembling many models — not that anyone reads the directions — always started by saying something like “Insert Tab A in Slot B.”

Oddly enough, that line reminds me of how odonates copulate, in general, and Cobra Clubtail dragonflies (Gomphurus vastus) in particular.

Male

The hamules are “Tab A.”

Female

The subgenital plate is “Slot B.”

Putting it all together

Insert Tab A in Slot B. That’s the PG-rated version of how Cobra Clubtail dragonflies copulate in order to reproduce.

The Backstory

There is an annual mass emergence of Cobra Clubtails during the first week-or-two of May at Riverbend Park. It’s a spectacular event worth seeing firsthand!

The following photo shows a dead female, one of several Cobra Clubtails that were trampled by groups of elementary school children visiting the park on 09 May 2017. Her premature death saddens me because it was avoidable — the students should have been warned to watch their step because there were lots of Cobra Clubtails perching on the ground almost everywhere.

In the hope the female didn’t die in vein, I reluctantly decided to photograph the corpse in order to illustrate her external reproductive anatomy.

Editor’s Note: Sincere thanks to Dennis Paulson for help in identifying the female parts on the ventral side of abdominal segments eight and nine (S8-9).

Copyright © 2017 Walter Sanford. All rights reserved.

Crayfish

May 26, 2017

A crayfish was spotted in the shallows of Bull Run, under several inches of water. I estimate it was 3-4 in (~7.6-10.2 cm) in length.

Many crayfish can be particularly hard to identify from a photograph and many new species are still being discovered in Virginia’s waterways. This large crayfish is from the Family Cambaridae and is likely a native species. Other crayfish found in Northern Virginia, like the rusty crayfish (Orconectes rusticus) and red swamp crayfish (Procambarus clarkii), were likely introduced via the food industry and pose a serious threat to native crayfish populations. Source Credit: John Burke, Ecologist III, Stormwater Management Branch, Fairfax County Department of Public Works and Environmental Services.

10 MAY 2017 | Fairfax County, VA | crayfish (underwater)

Notice the first, second, and third pairs of walking legs feature chelae (plural).

A chela /kˈiːlə/, also named claw, nipper, or pincer, is a pincer-like organ terminating certain limbs of some arthropods. The name comes from Greek (χηλή) through New Latin (chela). The plural form is chelae. Legs bearing a chela are called chelipeds. Source Credit: Chela (organ), Wikipedia.

Also notice the slimy stuff on the rocks that makes them super slippery!

The slimy, slippery coating you find on rocks in aquatic systems is periphyton. In freshwater systems, periphyton is mostly comprised of algae but other microorganisms and detritus also collect on submerged rocks. Periphyton serves as an essential food source to many aquatic organisms and can also act as a bioindicator, signaling changes in water chemistry and nutrient levels in the system (Chetelat et al. 1997). Source Credit: John Burke.

Tech Tip:  My Canon 580EX Speedlite external flash unit was set for 1/16 power in order to penetrate the water and illuminate the subject on a bright, sunny day.

Copyright © 2017 Walter Sanford. All rights reserved.

Common Baskettail (terminal appendages)

May 18, 2017

A male and female Common Baskettail dragonfly (Epitheca cynosura) were spotted recently at the same location in Fairfax County, Virginia USA.

Male and female Common Baskettails look similar. Terminal appendages can be used to identify gender.

Male

Male dragonflies have three terminal appendages, collectively called “claspers,” that are used to grab and hold female dragonflies during mating: an upper pair of cerci (“superior appendages”); and a lower unpaired epiproct (“inferior appendage”).

03 MAY 2017 | Fairfax County, VA | Common Baskettail (male)

(See a full-size version of the original photo, without annotation.)

Female

Female dragonflies have a pair of cerci (superior appendages) that have little or no function. The abdomen of female Common Baskettails is noticeably thicker than males of the same species.

03 MAY 2017 | Fairfax County, VA | Common Baskettail (female)

(See a full-size version of the original photo, without annotation.)

A better view of the subgenital plate is provided by the following digital scan of the underside of the abdomen of a female Common Baskettail. The subgenital plate looks a little like a pair of calipers. Also known as vulvar lamina, the subgenital plate is located under the ninth abdominal segment (S9) of some female odonates and “serves to hold eggs in place during exophytic oviposition.” Remember that all dragonflies and damselflies have a 10-segmented abdomen, numbered from front to back.

Image used with permission from Ed Lam.

Copyright © 2017 Walter Sanford. All rights reserved.

Lancet Clubtail dragonflies (males)

May 14, 2017

At least two Lancet Clubtail dragonflies (Phanogomphus exilis) were spotted during a photowalk along a mid-size stream in Fairfax County, Virginia USA.

03 MAY 2017 | Fairfax County, VA | Lancet Clubtail (male)

These individuals are males, as indicated by their terminal appendages and indented hind wings.

03 MAY 2017 | Fairfax County, VA | Lancet Clubtail (male)

The next photograph was taken at a later time than the first two photos. All of the photos in this post were taken near the same location. Is this another male, or the same one featured in the preceding photos? Who knows?

03 MAY 2017 | Fairfax County, VA | Lancet Clubtail (male)

Lancet Clubtail versus Ashy Clubtail

Lancet Clubtail looks similar to Ashy Clubtail (Phanogomphus lividus). The only way to differentiate the two species with certainty is to examine their external reproductive anatomy; this is impossible unless the specimens are captured and examined in-hand.

Relative size is used sometimes to identify the two species: Lancet Clubtail is slightly smaller than Ashy Clubtail. There are two problems with this method of identification. First, it is virtually impossible to determine the exact size of a specimen in the field unless it is captured and measured. Second, some natural variation in size should be expected among individuals of the same species.

A quick-and-dirty method for differentiating Lancet- and Ashy Clubtails with some degree of certainty is to look at the markings on abdominal segments eight and nine (S8-9). Lancet Clubtail has a “spearpoint” on top of abdominal segment eight (S8) that almost reaches the end of the segment, a wide yellow stripe on top of segment nine (S9), and irregular yellow markings on the sides of segments eight and nine (S8-9).

03 MAY 2017 | Fairfax County, VA | Lancet Clubtail (male)

(See a full-size version of the original photo, without annotation and inset photo of Ashy Clubtail.)

In contrast, Ashy Clubtail has a spearpoint on top of abdominal segment eight (S8) that is less than half the length of the segment, segment nine (S9) may or may not have a pale yellow stripe on top, and the sides of segments eight and nine (S8-9) may or may not have “poorly defined” yellow markings.

03 MAY 2017 | Fairfax County, VA | Ashy Clubtail (male)

(See a full-size version of the original photo, without annotation.)

Coloration is variable among individuals of the same species, so looking at abdominal markings isn’t always a reliable method of identification. In this case, it works beautifully.

Editor’s Note: The word “spearpoint” and the phrase “poorly defined” are descriptors attributed to Dennis Paulson, Dragonflies and Damselflies of the East (Princeton Field Guides). Princeton University Press. Kindle Edition.

Copyright © 2017 Walter Sanford. All rights reserved.

Spine-crowned Clubtail (terminal appendages)

May 10, 2017

A male and female Spine-crowned Clubtail dragonfly (Hylogomphus abbreviatus) were spotted recently in Fairfax County, Virginia USA.

Male

Male dragonflies have three terminal appendages, collectively called “claspers,” that are used to grab and hold female dragonflies during mating: an upper pair of cerci (“superior appendages”); and a lower unpaired epiproct (“inferior appendage”). The epiproct for Spine-crowned Clubtail is essentially a wide plate with two prongs.

03 MAY 2017 | Fairfax County, VA | Spine-crowned Clubtail (male)

(See a full-size version of the original photo, without annotation.)

The hind wings of male clubtail dragonflies are “indented” near the body, as shown in the preceding photograph. In contrast, the hind wings of female clubtails are rounded (shown below). Also notice the right hind wing of the male is slightly malformed.

Female

Female dragonflies have a pair of cerci (superior appendages) that have little or no function. The abdomen of female Spine-crowned Clubtails is noticeably thicker than males of the same species.

03 MAY 2017 | Fairfax County, VA | Spine-crowned Clubtail (female)

(See a full-size version of the original photo, without annotation.)

Copyright © 2017 Walter Sanford. All rights reserved.

Spine-crowned Clubtail dragonfly (male)

May 8, 2017

A Spine-crowned Clubtail dragonfly (Hylogomphus abbreviatus) was spotted recently in Fairfax County, Virginia USA. Spine-crowned Clubtail is relatively uncommon in Northern Virginia, and a new species of dragonfly for my life list.

This individual is a male, as indicated by his terminal appendages and indented hind wings. Notice the right hind wing is slightly malformed.

Spine-crowned Clubtail versus Cobra Clubtail

Spined-crowned Clubtail looks similar to Cobra Clubtail (Gomphurus vastus). Two field markers can be used to differentiate the species.

Spine-crowned Clubtail features large yellow spots on the sides of abdominal segments eight and nine (S8-9); Cobra Clubtail has a small yellow spot on the side of abdominal segment eight (S8) and a large yellow spot on the side of abdominal segment nine (S9), as shown below (see inset photo).

03 MAY 2017 | Fairfax County, VA | Spine-crowned Clubtail (male)

(See a full-size version of the original photo, without annotation and inset photo.)

The face of Spine-crowned Clubtail is yellow and unmarked; the face of Cobra Clubtail is yellow with horizontal black markings (see inset photo).

03 MAY 2017 | Fairfax County, VA | Spine-crowned Clubtail (male)

(See a full-size version of the original photo, without inset photo.)

More photos, Spine-crowned Clubtail

This guy was a cooperative model as I followed him to several perches on rocks along a large stream.

03 MAY 2017 | Fairfax County, VA | Spine-crowned Clubtail (male)

03 MAY 2017 | Fairfax County, VA | Spine-crowned Clubtail (male)

03 MAY 2017 | Fairfax County, VA | Spine-crowned Clubtail (male)

03 MAY 2017 | Fairfax County, VA | Spine-crowned Clubtail (male)

Editor’s Notes: Special thanks to Mike Boatwright, curator of the Virginia Odonata Facebook group, for help in verifying my tentative field identification. As far as I know, this is the first official record for Hylogomphus abbreviatus in Fairfax County, Virginia.

Copyright © 2017 Walter Sanford. All rights reserved.


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