Had me stumped for a long time. I'll reveal the identity soon but curious to know if anyone else has seen something like this before? Let's make it a guessing game :D

Edit: reveal in the second image, prepare for a letdown.

Fall Armyworm Moth (Spodoptera frugiperda)

Avondale Park
Denton, Texas
August 3, 2014

Note: We want to acknowledge and thank John and Jane Balaban, Contributing Editors at BugGuide, for making this ID possible. They pointed us in the right direction and we were able to confirm their highly accurate suggestion that the subject of our observation was none other than Fall Armyworm Moth (Spodoptera frugiperda). To access the ID of this specimen at BugGuide go to: http://bugguide.net/node/view/1191162

We first observed this moth's caterpillar wading in about 1/8" to 1/4" inch of water in Cooper Creek next to Avondale Park in Denton, Texas. As the creek's current was not moving that day, it was able to navigate the depth of its immediate environment. Many songbirds stop to drink water in the vicinity of where this observation was made so it was dangerous for this caterpillar to be found at the location since it could easily become prey to the birds.

Species Spodoptera frugiperda - Fall Armyworm Moth - Hodges#9666

Once we received the probable ID from John and Jane Balaban we checked both past BugGuide IDs of Fall Armyworm Moth (Spodoptera frugiperda) as well as the North American Moth Photographers Group in order to confirm the ID. We checked the available (Texas-related) reports on BugGuide and there we found two previous reports of this species for the month of August (per the Data Map), one a caterpillar and its moth form in the other. Our present observation would be the second caterpillar for this species reported in August for Texas on BugGuide but the first for the North Texas region and Denton County specifically. The other two reports were made from Harris County, which is the Houston metro area, nearly 300 miles distant southeast from our location. The BugGuide caterpillar for Harris County though is a perfect match for our entry and so is another located at the North American Moth Photographers Group online site. Hence we were able to confirm the ID for this caterpillar as that of the Fall Armyworm Moth (Spodoptera frugiperda).

Fall Armyworm Moth is found throughout the eastern half of the United States and the US Southwest as well as Ontario, Canada adjoining the US, the Caribbean nations and Cuba in particular, Mexico, and Central America. Because of its extensive North American range, Fall Armyworm Moth is an authentic resident of the Western Hemisphere. Avondale Park and Cooper Creek are administered by the City of Denton, Texas.

Sources:

“Fall Armyworm Moth (Spodoptera frugiperda),” BugGuide, Department of Entomology, Iowa State University, photographs, range map, description, resource links, accessed 2.15.16, http://bugguide.net/node/view/40787/bgimage

“Fall Armyworm Moth (Spodoptera frugiperda),” North American Moth Photographers Group, Mississippi Entomological Museum, Mississippi State University, range map, photographs, accessed 2.15.16, http://mothphotographersgroup.msstate.edu/species.php?hodges=9666