Water spider

[iandvaag]

This really interesting spider was discovered just outside of Weyburn, Saskatchewan, Canada. The approximate coordinates are 49°39′40″N 103°51′9″W (68 miles north of the US-Canada border. It was discovered early afternoon on Saturday July 14th, 2012 in a box of water. The site has a floating tree nursery with plastic-lined boxes approximately 8 feet by 4 feet. These boxes are filled with water and duckweed is very prolific. The spider was found resurfacing from under the duckweed, floating a while and then diving underneath the duckweed again. I waited a few minutes after it dove, but did not see it resurface again. It measured perhaps 2 inches long.
Any help in identification is greatly appreciated. This website is fantastic by the way!
Ian

[Ungoliant]

Nice find! This is a six-spotted fishing spider (Dolomedes triton), named for the six spots on its sternum (the underside of the carapace). It's a member of the nursery web family (Pisauridae).

This species is semi-aquatic; it can walk on water and dive, as you have observed. They primarily eat aquatic bugs and tadpoles.

[iandvaag]

Thank you so very much for your prompt and informative reply! Very much appreciated!

[Mandy]

Looks like a female with an egg sac, too (the round, brownish object that she's practically floating on is an egg sac). She was probably diving as a defensive maneuver, maybe to escape your shadow or a passing bird or something. Their vision is not very sharp, especially more than a few feet away, but they can see shadows and sense changes in the wind.

Nice images, Ian, and welcome to the forum! :-)

[Ungoliant]

Looks like a female with an egg sac, too (the round, brownish object that she's practically floating on is an egg sac).

I was wondering if that was an egg sac!

[iandvaag]

Thanks so much for the information! Fantastic!

[acbaker]

Wow, Mandy and Ungoliant... great eye! I missed that altogether. I need to get more observant I think.

[Mandy]

I probably wouldn't have noticed if it weren't for the strange stance the spider has in the photos... I kept looking trying to figure out why. Then, aha! She's on top of a big round object. :-)