Posts Tagged ‘Family Cordulegastridae (Spiketails)’

Mouth parts – Tiger Spiketail exuvia

November 12, 2021

I revisited a photograph featured in a blog post published several years ago. I wanted to annotate the image to include information that I learned recently.

The following annotated image shows the face and mouth of an exuvia from a Tiger Spiketail dragonfly (Cordulegaster erronea) after its scoop-shaped face mask was pulled away from the head in order to count setae on the inner side of the prementum.

Cordulegaster erronea | exuvia (face and mouth)

There are two mandibles, one located on each side of the labrum. And there are two maxilla, one located below each mandible. Coarse setae make it challenging to see all of the parts clearly.

Sincere thanks to Marla Garrison for verifying my tentative identification of these mouth parts. And of course, thanks to Mike Boatwright for collecting and sharing the specimen with me.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

How to estimate instar

October 29, 2021

Most odonate larvae (nymphs) go through 10-13 stages of development known as “instars.” F-0 is the final instar, F-1 the preceding instar, and so forth.


The “F” in the name for every instar stands for Final. “F-0” is the final instar. “F-1” means final instar minus one, that is, the stage that precedes the final instar. “F-2” means two stages before the final instar.

Ken Tennessen, author of Dragonfly Nymphs of North America: An Identification Guide, devised a method for determining instar by examining hind wing length and head width.

Calculating the ratio between hind wing length and head width results in a number that is approximately equivalent to instar, that is, assuming you know how to interpret the result¹.

The equation for instar equivalent is as follows.

Instar equivalent = HwL / HW

Where HwL is Hind wing Length and HW is Head Width.

Math Tips

Fractions are read from top-to-bottom, or when written as shown above, left-to-right. The equation literally says “Instar equivalent equals Hind wing Length divided by Head Width.”

The equation is units independent, meaning any units of measurement can be used as long as the same units are used above and below the dividing line. Instar equivalent is a dimensionless number because the units cancel during division. (Remember “dimensional analysis” from chemistry and physics?)

For most of the life of an odonate larva (nymph) its head is wider than the length of its wing pads. Therefore instar equivalent is calculated by dividing a smaller number by a larger number, resulting in a decimal fraction. As the wing pads grow, the instar equivalent increases until the ratio is approximately 1:1 (or slightly larger) at F-0, the final instar.

¹According to empirical data collected by Tennessen, average instar equivalents are as follows: ≥1.00 for F-0; 0.66 for F-1; 0.50 for F-2; 0.33 for F-3; and 0.25 for F-4. Remember, these numbers are averages — your mileage might vary.

Theory into practice

Cordulegaster sp. larva (female) | dorsal view

I used the Adobe Photoshop “Ruler Tool” to measure the number of pixels along the two double-tipped white arrows shown in the preceding annotated image of a preserved specimen.

Tech Tips

60s ‘shop: Using the ruler tool to measure distances in Photoshop CC, by Photoshop for the Scientist (1:00) provides a clear and concise explanation of how it’s done.

HwL is ~920.81 pixels. HW is ~911.15 pixels.

Instar equivalent = 920.81 pixels / 911.15 pixels

The units cancel, so the answer is ~1.01 — close enough to the average value for F-0 (final instar). Easy, huh?

What are the take-aways?

  1. An instar of F-0 indicates the spiketail larva featured in this blog post was nearer the end of the larval phase of its life than the beginning. Time is dilated for larvae in the Family Cordulegastridae (Spiketails), so it’s difficult to say how much longer it would have been until the larva metamorphosed into an adult.
  2. Every odonate exuvia is a cast skin of the larva at F-0, the final instar, before it ecloses to become an adult. Therefore the instar equivalence for all exuviae should be ≥1.00. Try it and see!

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Cordulegaster sp. larva

October 22, 2021

Odonates are aquatic insects. They spend most of their life as larvae (nymphs) that live in water; this stage of their life cycle can last from a few months to a few years. Finally, they emerge from the water and metamorphose into adults in order to reproduce; their offspring return to the water and the cycle begins again.

This post features annotated images of a larva (nymph) from the Family Cordulegastridae (Spiketails) that was collected and reared by Bob Perkins. The larva died before it metamorphosed into an adult.

The distinctive jagged crenulations on the face mask of spiketails are unmistakeable!

Cordulegaster sp. larva (preserved specimen) | face-head

This individual is a female, as indicated by her developing ovipositor that can be seen on the ventral side of the specimen along the boundary between abdominal segments eight and nine (S8, S9).

Cordulegaster sp. larva (female) | ventral view

The presence of a ventromedial groove in the prementum is a reliable field mark for larvae/exuviae in Family Corduliidae (Emeralds). Some species of larvae/exuviae in other families of dragonflies, such as Family Cordulegastridae (Spiketails), feature a ventromedial groove in the prementum. In this case, the presence of a ventromedial groove does not indicate this specimen is an Emerald.

Most odonate larvae go through 10-13 stages of development known as “instars.” The author lacks sufficient experience to identify the instar of this specimen, although it appears to be one of the later stages as indicated by its well-developed wing pads, shown below.

Post Update: According to Ken Tennessen, author of Dragonfly Nymphs of North America: An Identification Guide, F-0 is the instar of this specimen (final instar). Thanks, Ken!

Cordulegaster sp. larva (female) | dorsal view

Larvae (nymphs)/exuviae in Family Cordulegaster (Spiketails) are burrowers, as indicated by the dirty, sediment-covered dorsal side and relatively clean ventral side of this specimen.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Anatomy of a male Tiger Spiketail

August 10, 2021

The following annotated image shows a Tiger Spiketail dragonfly (Cordulegaster erronea). This individual is a male, as indicated by his hamules, “indented” hind wings, and terminal appendages.


Hamules? What are hamules?

hamules: paired structures that project from genital pocket under second segment and hold female abdomen in place during copulation Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 11618-116198). Princeton University Press. Kindle Edition.

Male dragonfly secondary genitalia, called hamules, are located below abdominal segments two and three (S2 and S3), as shown in the following annotated image. Hamules come in a variety of sizes and shapes, but their function is identical for all species of odonates. Some species of dragonflies and damselflies — such as Ashy Clubtail versus Lancet Clubtail and Southern Spreadwing versus Sweetflag Spreadwing, to name a few — can be differentiated/identified with certainty only by examining the hamules under magnification.

Photo used with written permission from Michael Powell.

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

Indented hind wings

Male members of many families of dragonflies have “indented” hind wings near the body, with some notable exceptions.

Hind wing venation and shape can identify the sex of most dragonflies. Petaltails, darners (except Anax), clubtails, spiketails, cruisers, and some emeralds. Wing shape isn’t helpful to sex baskettails since they are largely the same. They are different in Cordulia, Dorocordulia, Somatochlora and to a lesser degree, Neurocordulia. Source Credit: Ed Lam, author and illustrator of Damselflies of the Northeast.

Terminal appendages

Identifying female versus male dragonflies and damselflies can be challenging but it’s a little easier when you know how to differentiate their terminal appendages.

All 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”). Male dragonfly terminal appendages don’t look exactly the same for all species of dragonflies, but their function is identical.

Generally speaking, spiketail dragonflies have relatively small terminal appendages. That said, they must get the job done!

Related Resource: Tiger Spiketail dragonfly (male) – a blog post by Walter Sanford.

Copyright © 2021 Walter Sanford. All rights reserved.


Tiger Spiketail dragonfly (male)

August 7, 2021

Tiger Spiketail dragonfly (Cordulegaster erronea) was captured along a small stream at an undisclosed location in Prince William County, Virginia USA. The specimen was photographed and released unharmed.

The first few images show Michael Powell, my former friend and photowalking buddy, holding the dragonfly while I shot some photographs.

05 AUG 2021 | Prince William County, VA | Tiger Spiketail (male)

This individual is a male, as indicated by his hamules, “indented” hind wings, and terminal appendages.

05 AUG 2021 | Prince William County, VA | Tiger Spiketail (male)

What a handsome face! Cue “Eye Of The Tiger” by Survivor.

05 AUG 2021 | Prince William County, VA | Tiger Spiketail (male)

The next image shows me holding the dragonfly so that Mike could take some photographs.

Photo used with written permission from Michael Powell.

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

Up, up, and away!

The last photograph shows the Tiger Spiketail “posed” au naturel on the trunk of a fallen tree. Mike and I chose that spot because it was one of only a few sunny places along the small forest stream. The Tiger flew away almost immediately after I released him, headed toward the tree canopy. Mike had time for one clear shot. Good thing, ‘cuz I had no opportunity to get a shot.

Photo used with written permission from Michael Powell.

The backstory

I went on my first Tiger safari during July 2018 when I visited a location in Fairfax County, Virginia that a friend shared with me in strictest confidence. Although I saw several Tiger Spiketail dragonflies, every individual was in flight and I was unable to shoot still photos and/or video — they were gone by the time I reached for my camera!

Every year for the next few years, the story was similar — I saw Tigers but had no photos/videos to verify my sightings. Eventually I came to the conclusion that I would need to capture a specimen with an insect net in order to take photographs.

Let me be perfectly clear — all things being equal I would prefer to photograph dragonflies perching naturally rather than netting them. Sometimes, as in this case, netting is the better way to go.

Rest assured I have great respect for the rare- to uncommon species of odonates. The Tiger Spiketail featured in this post was held in captivity no longer than absolutely necessary, and was handled gently at all times.

Our strategy

Mike and I arrived at the stream site sometime after 10 a.m. While I setup my 18” diameter collapsible insect net, Mike took the point a little farther downstream to look for a Tiger approaching our location. No more than 10 minutes after I was in position alongside the stream, Mike spotted a Tiger flying upstream in our direction.

I waited until the Tiger had almost reached the place where I was standing before I swung my net forward smoothly and was psyched to see the dragonfly go all the way into the net. I said to Mike, “I got it!”

From that point, I worked quickly to gently remove the dragonfly from the net so that Mike and I could take some photographs of this rare species.

Range map

The following map shows all official records for Cordulegaster erronea in the United States of America. Tiger Spiketail is a habitat specialist that is challenging to find.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

It’s all about habitat, habitat, habitat.

April 23, 2021

Small streams and seeps in the forest are perfect places to look for habitat specialist dragonflies such as petaltails and spiketails.

An old place revisited.

The following photograph of a forest seep has been featured in my blog at least once in the past. The seep feeds a small pond; Gray Petaltail dragonflies (Tachopteryx thoreyi) can be found feeding and perching in sunny spots around the pond during late-May and early-June.

23 MAY 2018 | Prince William County, VA | forested seep

The seep is the habitat where Gray Petaltail larvae live most of their lives, not the pond. I always wondered how so many adult petaltails could emerge from this relatively small seep.

Turns out Michael Powell, my good friend and photowalking buddy, must have been wondering the same thing because he explored the area upstream from the small seep shown above and discovered several more seeps located close to the one near the pond.

The next photo shows Mike resting on a log along the edge of one of the seeps, near the confluence of two small streams. Notice the patch of skunk cabbage (Symplocarpus foetidus) growing in the seep — a good sign that you might be looking at habitat suitable for Gray Petaltail.

13 APR 2021 | Prince William County, VA | forested seep

A new place worth exploring further.

Mike also discovered another small stream in the forest when he was exploring for Uhler’s Sundragon (Helocordulia uhleri). The stream is located at the approximate midpoint between two trails, so I nicknamed it “Middle Creek.” Clever, huh? Note the patch of skunk cabbage growing in a seep alongside the stream. Did an alarm just go off in your head?

13 APR 2021 | Prince William County, VA | forested stream and seep

Mike and I are eager to explore the stream further, mainly looking for Gray Petaltail during late spring. Several species of spiketails might be found there as well.

Copyright © 2021 Walter Sanford. All rights reserved.

Arrowhead Spiketail dragonfly (male)

June 17, 2020

An Arrowhead Spiketail dragonfly (Cordulegaster obliqua) was spotted during a recent photowalk with Michael Powell at a location in Fairfax County, Virginia USA.

08 JUN 2020 | Fairfax County, VA | Arrowhead Spiketail (male)

This individual is a male, as indicated by his hamules and terminal appendages.

08 JUN 2020 | Fairfax County, VA | Arrowhead Spiketail (male)

The Backstory

At the end of a long day in the field, Mike Powell and I were walking back to the car slowly when we spotted a group of 10-or-so large dragonflies hawking insects over a HUGE field, near a small drainage pipe. We stopped to watch the hawkers hoping one would land; I sat on my Coleman camp stool to rest in the shade and enjoy the aerial acrobatics show.

One of the large dragonflies zoomed past Mike (he says he never saw it) and landed on a tall grass stem near the drainage pipe. It was the male Arrowhead Spiketail shown above!

Turns out the place is nothing like the habitat described as ideal (see below). I’ll say this: Three out of four times I’ve seen Arrowhead Spiketails, a fly-by was how I found them. So maybe just sit in a good spot and wait for the game to come to you. Maybe.


Disclaimer: I have observed and photographed four (4) Arrowhead Spiketail dragonflies. I feel somewhat uncomfortable providing habitat guidance based upon a sample size of four. That being said, here goes.

Almost every Arrowhead siting had three common ingredients: a seep (or soggy place) in the forest, with skunk cabbage (Symplocarpus foetidus) and interrupted fern (Osmunda claytoniana); a small stream in the forest fed by the seep/soggy place; and a sunny clearing.

I found my first Arrowhead Spiketail at a small stream in Huntley Meadows Park. I walked the stream to its source, not that the source is well defined. Instead it’s a BIG soggy area. I wouldn’t call it a seep and I have never seen skunk cabbage anywhere in the park. There are two virtually identical streams elsewhere in the park where Arrowhead has been photographed. The male Arrowhead flew a LONG patrol along the stream, flying approximately six inches (6″) above the water level. At the end points of his patrol, he would hang up to rest in a sunny spot. It took a long time for me to find the hang up places!

Michael Powell spotted the second Arrowhead Spiketail I’ve seen, perched in a small, sunny clearing in the forest along a small stream. A seep with skunk cabbage and interrupted fern was located nearby. For what it’s worth, we saw/photographed several Gray Petaltail dragonflies (Tachopteryx thoreyi) in the same field.

MUCH FARTHER downstream, the same creek is a little larger in size. At one point, a small iron-stained creek flows into the main creek. Mike and I were standing at the mouth of the tiny creek when I saw an Arrowhead fly like a bat out of hell straight down the stream and turn left; it perched in a large, sunny field. I was able to find it, and we took photos. A week-or-so later, Mike traced the smaller creek to its source. Wouldn’t you know it? The headwaters are a seep with lots of skunk cabbage!

My most recent Arrowhead Spiketail sighting — the individual featured in this blog post — is the one that doesn’t fit the pattern. The dragonfly was spotted in a HUGE field of grasses, etc. There are small creeks and seeps nearby, but not within sight of the location where the Arrowhead perched.

Related Resources

Copyright © 2020 Walter Sanford. All rights reserved.

Gray Petaltail dragonfly (female)

August 16, 2019

A Gray Petaltail dragonfly (Tachopteryx thoreyi) was spotted during a photowalk with Michael Powell around a small seep-fed pond in the forest at an undisclosed location in Prince William County, Virginia USA.

This individual is a female, as indicated by her terminal appendages. She is perched on a small tree in a sunny clearing.

21 MAY 2019 | PNC. William County, VA | Gray Petaltail (female)

A seep is a seep is a seep.

Gray Petaltail is known to occur at a small, seep-fed pond located in the forest. Part of the seep is shown below. The female dragonfly featured in this blog post was perched on a small tree just to the left edge of the photo.

23 MAY 2018 | PNC. William County, VA | seep in the forest

Forest seeps vary in size and associated vegetation, but wherever you find one it provides good habitat for petaltails and some species of spiketails.

Copyright © 2019 Walter Sanford. All rights reserved.

Another seep deep in the forest

July 24, 2019

“Two-board Bridge” is located along a marked trail in the forest at an undisclosed location in Prince William County, Virginia USA. The small, wooden footbridge crosses a large seep. The plant with broad green leaves is skunk cabbage (Symplocarpus foetidus).

04 JUN 2019 | PNC. William County, VA | “Two-board Bridge”

Location, location, location.

Seepage areas in the forest are prime locations for hunting habitat-specific odonates such as petaltails and some species of spiketails.

The Backstory

DSA members Ken Larsen and Michael Ready saw and photographed a single male Sable Clubtail (S. rogersi) on 01 June 2010 in Prince William County. Nine years later, neither Ken nor Michael were able to recall the exact location of their sighting, but they were able to point me toward the general vicinity where I might “rediscover” one of the descendants of the Sable they’d seen.

I asked Mike Powell to help me hunt for Sable. Mike did some solo exploration before we visited the site together. He mentioned there is a LOT of skunk cabbage along one of the trails he had followed. As soon as I saw the place, Mike will tell you I said “We should find Gray Petaltail here.” Not long afterward, we spotted the first of many T. thoreyi!

Coming full circle, Mike spotted a single male Sable Clubtail dragonfly about a week later in the same “neighborhood.” We searched the location intensively several more times but never saw another Sable.

Although Sable doesn’t live in seeps, our search for the right habitat for Sable led us to several seeps that are tributaries of the small creek where S. rogersi does live.

Gear Talk

Notice the disjointed human legs at the top of the image — they belong to Mike Powell, my good friend and photowalking buddy. Sometimes I get so focused on the subject of interest that I don’t see the bigger picture. I could say I included Mike’s legs in order to provide a sense of scale, but the truth is it’s an unintended consequence of poor photo composition.

Also gotta love the blown highlights in the photo! The high dynamic range between the shadows of the forest canopy and direct sunlight would have been better photographed as an HDR composite image.

Related Resources

Copyright © 2019 Walter Sanford. All rights reserved.

Another Arrowhead Spiketail (female)

June 21, 2019

An Arrowhead Spiketail dragonfly (Cordulegaster obliqua) was spotted in a sunny clearing along a small-to-medium size forest stream at an undisclosed location in Prince William County, Virginia USA.

14 JUN 2019 | PNC. William County, VA | Arrowhead Spiketail (female)

This individual is a female, as indicated by her rounded hind wings, terminal appendages, and prominent ovipositor at the tip of her abdomen.

14 JUN 2019 | PNC. William County, VA | Arrowhead Spiketail (female)

Did you recognize the interrupted fern (Osmunda claytoniana) in the background of every photo in this gallery?

14 JUN 2019 | PNC. William County, VA | Arrowhead Spiketail (female)

The Backstory

Mike Powell and I stopped to use GPS to get a fix on our position at the end of a long photowalk that included lots of bushwhacking. We stopped because the small stream we were exploring was getting wider and deeper the farther we walked downstream, and we decided the stream habitat had changed to be less suitable for Sable Clubtail (S. rogersi), our target species.

The place where we stopped is a sunny meadow near the confluence of a tiny side stream with the larger stream we were following. As Mike was testing a few GPS apps for his Android cell phone, I noticed a big dragonfly as it flew down the tiny stream, turned left past us, and landed in the sunny meadow. I found the dragonfly after a few minutes of searching the area where I saw it land. I was hoping for a Tiger Spiketail (Cordulegaster erronea) but nonetheless delighted to see a female Arrowhead Spiketail — our second record of this species for the year at the remote location!

Related Resource: Arrowhead Spiketail dragonfly (female)

Copyright © 2019 Walter Sanford. All rights reserved.

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