Posts Tagged ‘Stream Cruiser dragonfly’

Beware of look-alikes!

September 28, 2021

Some species of dragonfly larvae/exuviae look similar to other species. Here are a couple of look-alikes from two different families that might fool you.

One species of Corduliidae in our region [North America], Epitheca princeps, resembles the macromiid general body shape and is nearly as large, but the legs are short compared to its body dimensions and it lacks a triangular frontal projection. Source Credit: K. J. Tennessen, Dragonfly Nymphs of North America, https://doi.org/10.1007/978-3-319-97776-8_10, Macromiidae, p. 329.

The first annotated image shows a ventral view of a Prince Baskettail (Epitheca princeps) exuvia. E. princeps is a member of Family Corduliidae (Emeralds).

Notice the appearance of the E. princeps exuvia is quite similar to the Stream Cruiser (Didymops transversa) exuvia shown below. D. transversa is a member of Family Macromiidae (Cruisers).

The E. princeps exuvia features lateral spines and well-developed mid-dorsal hooks on some abdominal segments. Notably “it lacks a triangular frontal projection” (K. J. Tennessen), or stated more simply, there isn’t a “horn” on its face-head.

The D. transversa exuvia also features lateral spines and mid-dorsal hooks, as shown below. Notice the mid-dorsal hooks aren’t as cultriform as E. princeps. In contrast to the E. princeps exuvia, notice the prominent “horn” on the face of the D. transversa exuvia. It’s all about the “horn.”

A “horn” on the face-head is a characteristic field mark for odonate larvae/exuviae in the Family Macromiidae (Cruisers).

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Macromiidae – It’s all about the “horn.”

September 24, 2021

A “horn” on the face-head is a characteristic field mark for odonate larvae/exuviae in the Family Macromiidae (Cruisers).

Look closely at the full-size version of each of the following photos and you should be able to see the horn on the face of a Stream Cruiser dragonfly (Didymops transversa) exuvia that was collected during mid-April 2021.

13 APR 2021 | PNC. William County, VA | Stream Cruiser exuvia (face-head)

It’s easier to see the horn in the next photo…

13 APR 2021 | PNC. William County, VA | Stream Cruiser exuvia (dorsal)

The horn is clearly visible in the last photo. Notice there are three “bumps” located between the eyes of the exuvia: the middle bump is the horn; the antennae bases are located to the left and right of the horn.

13 APR 2021 | PNC. William County, VA | Stream Cruiser exuvia (dorsal)

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Test shots: Didymops transversa exuvia

September 21, 2021

An exuvia from a Stream Cruiser dragonfly (Didymops transversa) was collected from one of the concrete abutments of a man-made dam located along a mid-size stream at an undisclosed location in Prince William County, Virginia USA.

I prefer to photograph odonate exuvia like this one “as is” — presumably its appearance is similar to the way larva looked when it lived underwater.

13 APR 2021 | PNC. William County, VA | Stream Cruiser exuvia (dorsal)

If so, then I’m guessing D. transversa larvae are bottom dwellers, as indicated by the dirty, sediment-covered dorsal side and relatively clean ventral side of this specimen.

13 APR 2021 | PNC. William County, VA | Stream Cruiser exuvia (ventral)

Post Update

The nymphs are sprawlers that cling to roots or hunker down in sediments of mixed sand and silt particles. Source Credit: K. J. Tennessen, Dragonfly Nymphs of North America, https://doi.org/10.1007/978-3-319-97776-8_10, Macromiidae, p. 330.

The Backstory

The preceding photos were shot using the prototype for a homemade curved clear plastic tray intended for staging subjects against a white background.

With a few minor tweaks, the curved stage performed better than during initial testing. I needed to add a second external flash unit to more evenly illuminate the white background.

Although I’m fairly satisfied with the results of these test shots, more testing is required to be sure the set-up is working the way I want.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Stream Cruiser dragonfly (female)

May 18, 2021

A Stream Cruiser dragonfly (Didymops transversa) was spotted during a recent photowalk with Michael Powell along a mid-size stream at an undisclosed location in Prince William County, Virginia USA.

This individual is a female, as indicated by her thick abdomen and terminal appendages.

13 MAY 2021 | Prince William County, VA | Stream Cruiser (female)

The female was perched in a large field near the same location where Mike Powell found a Stream Cruiser exuvia on 13 April 2021.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Exuvia from Family Macromiidae (Cruisers)

May 14, 2021

Michael Powell spotted a large odonate exuvia clinging to the concrete abutment of a man-made dam located along a mid-size stream at an undisclosed location in Prince William County, Virginia USA.

This cast skin is definitely from a member of Family Macromiidae (Cruisers), as indicated by its long legs and the shape of its body.

13 APR 2021 | Prince William County, VA | Stream Cruiser (exuvia)

Mike’s macro photo of the same subject (shown below) turned out better than mine, taken with a superzoom bridge camera. Look closely at the full-size version of Mike’s photo. Nothing says Family Macromiidae (Cruisers) like the “horn” on the front of the face/head of the exuvia!

Photo used with written permission from Michael Powell.

The following excerpt from Identification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz, shows the couplet that I think indicates this specimen is from a Stream Cruiser dragonfly (Didymops transversa).

The adult flight periods for the three species of cruisers found in Northern Virginia provide circumstantial evidence in support of my tentative identification. Source Credit: “Dragonflies of Northern Virginia” Web site by Kevin Munroe.

What’s next?

The specimen was collected in order to shoot a complete set of macro photographs of the exuvia in my home “studio.”

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Epitheca princeps exuvia

September 6, 2018

An odonate exuvia was collected by Michael Boatwright, founder and administrator of the Virginia Odonata Facebook group, on 07 June 2018 at Otter Lake in Amherst County, Virginia USA.

A two-step process was used to identify the genus and species of the specimen.

  1. Determine the family.
  2. Determine the genus and species.

Step 1. Family

First, determine the family of the specimen. For reference, watch the excellent Vimeo video, Identifying dragonfly larva to family (8:06). Here’s the decision tree used to identify the exuvia as a member of the Family Corduliidae (Emeralds).

  • The specimen has a mask-like labium (prementum) that covers the face, as shown in Image No. 1, characteristic of four families of odonates: Cordulegastridae (Spiketails); Corduliidae (Emeralds); Libellulidae (Skimmers); and Macromiidae (Cruisers).
  • There is no horn on the face-head, characteristic of Macromiidae, so it’s not a cruiser.
  • Cordulegastridae has jagged crenulations on its labium, so it’s not a spiketail. The crenulations for Corduliidae and Libellulidae look similar.
  • Look at the anal pyramid to differentiate Corduliidae and Libellulidae: It’s probably Corduliidae if the cerci are at least half as long as the paraprocts, as shown in Image No. 4. [Editor’s Note: It’s probably Libellulidae if the cerci are less than half the length of the paraprocts.]

In summary, the exuvia has a mask-like labium with relatively smooth crenulations, no horn on its face-head, and the cerci are more than half as long as the paraprocts, confirming that the specimen is a member of Family Corduliidae (Emeralds).

No. 1Epitheca princeps | exuvia (face-head)

Step 2. Genus and species

Characters from two dichotomous keys were used to identify the genus and species: Prince Baskettail dragonfly (Epitheca princeps). See Epitheca princeps exuvia, another of my illustrated guides to identification of odonate exuviae, for a detailed explanation of the decision tree used to identify the genus and species of this specimen.

No. 2 | Epitheca princeps | exuvia (dorsal)

This individual is a male, as indicated by the vestigial hamuli visible on the ventral side of abdominal segments two and three (S2-3).

No. 3Epitheca princeps | exuvia (ventral)

Notice the cerci are at least half as long as the paraprocts, as shown in Image No. 4.

No. 4Epitheca princeps | exuvia (posterior abdomen)

Image No. 5 shows a dorsal-lateral view of the mid-dorsal hooks.

No. 5Epitheca princeps | exuvia (dorsal-lateral)

Look-alike species

I really wanted this specimen to be Stream Cruiser dragonfly (Didymops transversa). I think exuviae from D. transversa and E. princeps are similar in appearance — an opinion not shared by at least one expert on identification of odonate exuviae.

Two characters proved to be the deal-breaker that forced me to abandon D. tranversa in favor of E. princeps. 1) The specimen does not have a horn on its face-head. 2) This specimen is only 25 mm long (2.5 cm); D. transversa larvae/exuviae are 30 mm long (3.0 cm), according to Dragonflies of North America, Needham, James G., et al.

Related Resources

Odonate Exuviae – a hyperlinked list of identification guides to many species of odonate exuviae from seven families of dragonflies and three families of damselflies.

Tech Tips

The following equipment was used to shoot Image No. 1-5: Canon EOS 5D Mark II digital camera, in manual mode; Kenko 20mm macro automatic extension tubeCanon EF100mm f/2.8L Macro lens (set for manual focus); Canon MT-26EX-RT Macro Twin Lite set for “Master” mode, and Canon 580 EX- and Canon 580EX II Speedlites set for “Slave” mode.

Image No. 1-5 are focus-stacked composite images created and annotated using Adobe Photoshop CC 2017: Image No. 1 (7 photos); Image No. 2 (22 photos); Image No. 3 (19 photos); Image No. 4 (10 photos); Image No. 5 (20 photos).

Copyright © 2018 Walter Sanford. All rights reserved.

Green-eyed Stream Cruiser

May 12, 2017

Stream Cruiser dragonfly (Didymops transversa) was spotted during a photowalk along a mid-size stream in Fairfax County, Virginia USA. This individual is a male, as indicated by his terminal appendages and indented hind wings.

03 MAY 2017 | Fairfax County, VA | Stream Cruiser (male)

Male: Eyes brown with green highlight above. … Female: Eyes brown. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 7192, 7194-7195). Princeton University Press. Kindle Edition.

I’ve never seen a green-eyed Stream Cruiser like this one — every one had brown eyes, including both males and females.

Copyright © 2017 Walter Sanford. All rights reserved.

Stream Cruiser dragonfly (male)

April 14, 2017

Another Stream Cruiser dragonfly (Didymops transversa) was spotted during a photowalk along Beaver Pond Loop Trail at Accotink Bay Wildlife Refuge, Fairfax County, Virginia USA.

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

Stream Cruiser dragonflies typically perch at a 45° angle because of their extremely long legs, especially noticeable in the last photo.

For another perspective on the same male, both literally and figuratively, see Stream Cruiser dragonfly by fellow photoblogger Michael Powell.

Copyright © 2017 Walter Sanford. All rights reserved.

Stream Cruiser dragonfly (female)

April 12, 2017

A Stream Cruiser dragonfly (Didymops transversa) was spotted during a photowalk along Beaver Pond Loop Trail at Accotink Bay Wildlife Refuge, Fairfax County, Virginia USA.

This individual is a female, as indicated by her rounded hind wings and terminal appendages. Look closely at the face and head of the dragonfly. Can you see why “ice cream sandwich face” is my nickname for Stream Cruiser?

The female landed long enough for me to shoot four photos before she flew away — not enough time for me to point her out to Michael Powell, a fellow amateur wildlife photographer and blogger who joined me in search of his first Stream Cruiser. Fortunately, Mike and I were able to photograph a male Stream Cruiser later the same afternoon. Look for photos of the male in my next blog post.

Addendum

I cropped the photo into a square format in order to remove a distracting element. Can you tell what I dislike about the original version? I prefer the square format. Which version do you prefer?

Copyright © 2017 Walter Sanford. All rights reserved.

Another female Stream Cruiser?

May 9, 2016

It’s possible the female Stream Cruiser dragonfly (Didymops transversa) in this gallery — spotted on 20 April 2016 at Accotink Bay Wildlife Refuge — is the same individual featured in a photoblog post published on 23 April 2016.

A Stream Cruiser dragonfly (Didymops transversa) spotted at Accotink Bay Wildlife Refuge, Fairfax County, Virginia USA. This individual is a female.

This is the second photo set that I shot of female Stream Cruisers spotted along the same segment of Beaver Pond Loop Trail. Although the two female dragonflies were perching on opposite sides of the trail, this female could be the same one that I spooked a few minutes earlier when I moved too close for her comfort.

A Stream Cruiser dragonfly (Didymops transversa) spotted at Accotink Bay Wildlife Refuge, Fairfax County, Virginia USA. This individual is a female.

This individual is a female as indicated by the pair of white terminal appendages (cerci) at the end of her abdomen, clearly visible in the following photo.

A Stream Cruiser dragonfly (Didymops transversa) spotted at Accotink Bay Wildlife Refuge, Fairfax County, Virginia USA. This individual is a female.

Stream Cruiser dragonflies have extremely long legs, especially noticeable in the last photo. The abdomen of female Stream Cruisers is thicker than males of the same species, similar to many species of odonates.

A Stream Cruiser dragonfly (Didymops transversa) spotted at Accotink Bay Wildlife Refuge, Fairfax County, Virginia USA. This individual is a female.

Copyright © 2016 Walter Sanford. All rights reserved.


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