Potomac River at Point-of-Rocks and Lander Boat Launch on Math 4th

[odona...@comcast.net]

To me one of the greatest annual Natural History events that take place in Maryland is the mass emergence of the Cobra Clubtails along the Potomac River.  Each year around this time an upstream one-hundred-mile wave of emerging Cobras starts around Washington D.C. and moves eastward well into Allegany County. Millions of Cobras emerge from the Potomac River each spring.  It is not uncommon to find a single tree trunk with 20 to 40 cast skins clinging to the bark in areas of high productivity near the river. Birds and mammals fill their bellies with emerging dragonflies at this time.  Even a fair number of fishermen use the easily caught emerging dragonflies as fish bait.

If the numbers of dragonflies are not impressive enough young adult Cobras are beautifully colored.  I think they are one of the most attractive dragonflies in Maryland.  The name “Cobra” comes from the behavior of the males raising their abdomens in the air and waving their enlarged abdominal club.

I visited the Potomac River in Frederick County last Monday (May 4th) at Point-of-Rocks and Lander Boat Launch in my last of the year search for the Chesapeake Clubtail (Ophiogomphus susbehcha or near).  Although none were found (it is a bit late for them anyway), the beginning of the Cobra Clubtail emergence made my day.

Mixed in with the Cobras were other gomphids as well. Walking the fields at Lander and collecting cast skins along the Potomac I found a Midland Clubtail, a Spine-crowned Clubtail, two Ashy Clubtails and a single cast skin of an Appalachian Snaketail.  This later find was the most unexpected. When I originally collected the skin, I thought it was a Rusty Snaketail, a species that is common a hundred miles upstream but one only rarely encountered this far downstream in the Potomac.  It was not until I examined it under the dissecting scope back in the lab did I notice that it was an Appalachian Snaketail.  This is the first Appalachian Snaketail taken from the Potomac River (note -- it was just downstream from the mouth of Catoctin Creek  so the larva may have drifted into the Potomac River from there).  It was also a new Frederick County Record for this species.  The Appalachian Snaketail is normally found further east in Maryland around the Fall Line separating the Piedmont and the Western Coastal Plain.

The fields at Lander Boat Launch are an excellent site for finding and photographing maturing Potomac gomphids.  I do need to warn everyone that by the beginning of May the fields are difficult to navigate due to massive stands of nettles and numerous Woodchuck holes hiding under the thick vegetation.  If you do go, keep an eye out for Lancet and Rapids Clubtails.  These species were expected but I failed to find them on the May 4th visit.

ODONATES SEEN:

Powdered Dancers (Argia moesta) – 18 – all tenerals -- netted to make the identification

Blue-tipped Dancers (Argia tibialis) – 3 – tenerals -- netted to make the identification

Other unidentified Argia species – 100+ -- emerging in mass from the river but not identified

Fragile Forktails (Ischnura posita) – 9

Spine-crowned Clubtail (Hylogomphus abbreviatus) – 1 teneral

Midland Clubtail (Gomphurus fraternus) – 1 adult female

Cobra Clubtails (Gomphurus vastus) – 35+ all tenerals to young adults and 32 cast skins – See: Cast Skin of Cobra Clubtail | Cast Skin of Cobra Clubtail (G… | Flickr & Cobra Clubtail -- Side View | Male Cobra Clubtail (Gomphurus… | Flickr & Cobra Clubtail -- Top View | Male Cobra Clubtail (Gomphurus … | Flickr 

Teneral Gomphids – 100+ seen usually in flight but not identified, but most likely Cobras

Ashy Clubtails (Phanogomphus lividus) – 2 mature adults

Appalachian Snaketail (Ophiogomphus incurvatus incurvatus) – 1 cast skin – See: Appalachian Snaketail on the Potomac River | This was the be… | Flickr  

Springtime Darner (Basiaeschna janata) – 1 mature adult

Stream Cruiser (Macromia transvera) – 2 mature adults

 

BUTTERFLIES SEEN:

Eastern Tiger swallowtails – 3

Zebra Swallowtails – 2

Spicebush Swallowtail – 1

Cabbage Whites – 6

Red-banded Hairstreaks – 2

Eastern Tailed Blues – 3

Pearl Crescents – 2

Red Admirals – 4

Silver-spotted Skipper – 1

Zabulon Skippers – 3 – my first for the year – See: My First Zabulon Skipper for 2026 | Male Zabulon Skipper on … | Flickr 

MOTH

Eight-sp0tted Forester — 1 — See: Eight-Spotted Forester from the Front | Eight-spotted Forest… | Flickr 

Richard Orr

[Jeff Cagle]

That's really cool!  Thanks for sharing.

Jeff