[Odonata-l] Planiplax (and more) in Texas! RFI

[Nick and Ailsa Donnelly]

Planiplax, esp sanguiniventris, and Erythemis peruviana look startling
alike.  There is a strong difference in their habits.  Erythemis perches
commonly along the shore, saying "Photograph me!", which I have done several
times, as have many of you.  The various species of Planiplax (I have found
four) rarely do this.  They tend to fly out over water, and their favorite
perches tend to be on small grass stems or sticks far from the shore.  They
seem difficult to approach.

There are several differences in specimens in the hand, of which the legs
(stout with heavy femoral spines in Erythemis, and thinner, with no stout
spines in Planiplax) are the most obvious.  There are important venational
differences, which I suspect cannot be photographed easily.  The very small
difference in the spot in the base of the hind wing is probably not useful
in identification, as these spots tend to vary considerably right through
the entire family.  Erythemis has the second abdominal segment mainly dark,
and planiplax has all segments red.

I am a little sceptical of the ID.  I would suggest that the most convincing
difference in a photo would be the legs.

Nick Donnelly

-----Original Message-----
From: odonata-l-bounces at listhost.ups.edu
[mailto:odonata-l-bounces at listhost.ups.edu] On Behalf Of
opihi at mindspring.com
Sent: Friday, June 06, 2008 12:42 AM
To: Odonata-l
Subject: [Odonata-l] Planiplax (and more) in Texas! RFI

Howdy folks,

We have been having some big excitement this week at Bentsen-Rio Grande
Valley State Park (in extreme southern Texas). A dragon, possibly more than
one, which I initially mistook from photos as Erythemis peruviana, has
turned out instead to be Planiplax, a genus never before recorded in the US!
Photos by Jan and David Dauphin, who first discovered the critter, are on
their website here: 

http://outdoors.webshots.com/album/540330134EjHYsB?start=72

This dragon was first spotted on Monday 6-2-08, and has been seen each day
since. The Dauphins initially reported 2 and perhaps as many as 4; I have
yet to see more than one, but the resaca where it has been lurking is
swarming with Red-tailed Pennants (Brachymesia furcata), as well as a number
of other brilliant red Libellulids, and while a Planiplax leaps out of the
crowd when it passes nearby, it could be easily missed at a distance of more
than a few meters.

The most likely species is P. sanguiniventris, according to Needham,
Westfall, and May the only member of the genus recorded from the Mexican
states nearest the US. However, we have been stymied in attempts to obtain a
specimen to confirm this. I have spent over three hours at the boat ramp,
the site of all observations so far, and seen the critter exactly twice. The
Dauphins, who have been able to spend far more time searching than I,
confirm that they see it roughly once per hour. These once-hourly sightings
are uniformly very brief, never more than a few seconds, and only twice in
the dozen or so encounters has it ever been seen to perch. Otherwise it
remains stolidly offshore. Even getting photos has been impossible in all
but one case, and none of us has even gotten close to swinging a net at the
little bugger.

Which brings me to my first question: Does anyone out there have experience
with this species in the field that might help us in trying to capture one,
or at least explain why it is so elusive? Martin Reid, who saw it with us
today, hypothesized that it might be patrolling the entire wetland, passing
by once per hour because it takes it that long to circumnavigate the entire
resaca (a.k.a. an oxbow lake, a long and winding body of water). Our other
thought is that it might be hiding out somewhere, maybe in the shade, maybe
too far offshore to be picked out of the masses of B. furcata, and not
visiting the boat ramp often; or that it might actually be sensitive to
human presence, refusing to perch or remain for long in the boat ramp
vicinity because of the persistent human presence there. Any of these
theories sound consistent with this genus' behavior where it is more common
further south?

More to the story: the Planiplax is far from alone. In addition to this
first-for-the-US occurrence, we have seen, over the past few days, a first
Texas record Metallic Pennant (Idiataphe cubensis), a first LRGV record
Antillean Saddlebags (Tramea insularis), first park records of Black
Pondhawk (Erythemis attala) and Three-striped Dasher (Micrathyria didyma),
and rare but not unprecedented species that, in any other week, might have
been the highlight odonate, such as Tawny Pennant (Brachymesia herbida),
Pin-tailed Pondhawk (E. plebeja), Checkered Setwing (Dythemis fugax),
Narrow-striped Forceptail (Aphylla protracta), and Halloween Pennant
(Celithemis eponina - an abundant species further north but decidedly rare
in the LRGV).

This astounding collection of species seems far beyond what could happen by
mere coincidence, and I have spent too much time watching odonates at this
particular boat ramp over the past two-and-a-half years to attribute this to
increased observer attention. I have heard butterfly-watchers relate
occurrences of rare Mexican butterflies to strong southwesterly winds
following autumn cold fronts. We have had very strong southeasterly winds
over the past few days, and several of the species involved seem to have
Caribbean affiliations (I. cubensis and T. insularis especially). Does this
seem like a sound explanation for this occurrence, or does anyone have an
alternative explanation for why so many rarities might appear at the same
time?

Thanks in advance for any insights that anyone can provide. And thanks also
for reading this far, this e-mail really turned into something of an epic...

Cheers,

Josh


Joshua S. Rose, Ph.D.
Natural Resource Specialist
World Birding Center
Bentsen-Rio Grande Valley State Park
http://www.worldbirdingcenter.org/sites/mission/index.phtml
joshua.rose at tpwd.state.tx.us
956-584-9156 x 236

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