Excerpts from Jim Conrad's
Naturalist Newsletter

from the June 28, 2018 Newsletter issued from Rancho Regenesis in the woods ±4kms west of Ek Balam Ruins; elevation ~40m (~130 ft), N~20.876°, W~88.170°; central Yucatán, MÉXICO
THAUMASIA, A NURSERY WEB SPIDER
While sitting beside the rancho's cement-lined pond waiting for something to happen, a fair-sized green spider skated across the water's surface and took up position on a floating leaflet, as shown below:

cf. Thaumasia

Back in Texas we've seen an aquatic spider with similar shape, white lines along the front part (the cephalothorax), and white spots along the top of the abdomen at the rear, but it wasn't green. You can compare our Yucatan spider with the Texas one at www.backyardnature.net/n/a/fishspid.htm

The Texas one was identified as the Six-spotted Fishing Spider, Dolomedes triton, and is commonly found throughout much of North America, plus it's known to occur in Mexico, though I can't find mention of the species in the Yucatan. Also, they're not green.

The North American ones and our Yucatan ones are so similar structurally that I can't imagine that they belong to different genera. However, I can't find any Dolomedes species looking like ours listed for the Yucatan. So here's another instance of "maybe we have something new."

*UPDATE: In 2018 I posted this page under the genus name "Dolomedes, admitting that I wasn't sure about it. In 2025, when the image is posted to the iNaturalist website, user "jeremyhussell" recognized the genus Thaumasia, but couldn't say what species it might be. I annotated the observation with this:

"After @jeremyhussell mentioned Thaumasia, I agree that it looks more like that genus, though I find no species matching our picture. Wikipedia's Thaumasia page, citing "Gloor, Daniel; Nentwig, Wolfgang; Blick, Theo; Kropf, Christian (2019). 'Gen. Thaumasia Perty, 1833.' World Spider Catalog Version 20.0. Natural History Museum Bern," list 17 known Thaumasia species, of which only two are described as occurring in Mexico. Neither of those appear to be our species. Maybe we have something interesting here."