Wednesday, September 11, 2013

Dolomedes albineus, a spider NEW (almost) to Ohio!

Last Sunday, while exploring a scruffy little patch of successional  habitat in Adams County, I glanced into the boughs of a Redbud tree to see a giant spider peering back. I was probably 20 feet or so distant and the spider was still obvious; that's how big this beast was. I took the photo above from a ways back, and you can get a feel for the arachnid's size based on comparison with the redbud leaves.

Right away I was reminded of a fishing spider in the genus Dolomedes, but ten feet up in a tree seemed an odd place for one of these stream and pond dwellers. Furthermore, it appeared that the spider had a nest up in the tree, and was guarding it. Indeed, as I approached, the spider moved out from the foliage as if to guard her den. Not too put off by her intimidating attitude, I moved in for photos...

By balancing precariously on some old wood, I was able to get closer to her level and make a series of images. A close inspection intrigued me. Now I was sure it was one of the nursery web spiders and almost certainly a fishing spider. But I had never seen one like this! Other than its large size - this animal would fill your palm, counting the leg spread - it had a striking blond head. Quite a showy animal indeed. She was guarding a nest as well, but I don't think the egg case had yet hatched.

Upon my return to Columbus, I cracked the books and it didn't take long to determine that the mystery spider was Dolomedes albineus (don't know a good common name, although I would suggest "Blond-headed Fishing Spider"). This species is somewhat variable, and my specimen has far more of a pale cephalothorax (head) than many or most of them.

A closeup showing the neat eye arrangement of Dolomedes fishing spiders: two rows, four eyes in each.

From the information that I could glean, it seemed that D. albineus would or should occur to the south of Ohio. So I sent some images off to Rich Bradley, a spider expert and author of THIS BOOK. Rich is always helpful and he responded quickly, confirming the identification. He was also excited by the find, as this is only the second reported record of this spectacular fishing spider in Ohio! The other was also photo-documented a few years ago, in Perry County I believe.

Dolomedes albineus is one to watch for, especially in southernmost Ohio. It seems to be expanding its range northward, along with a whole host of other small animals, especially insects. Low shrubby growth in the general vicinity of ponds or other water features might be a likely place to discover them.


Lisa at Greenbow said...

Congrats on your find. Great photos too.

Erik said...

Very nice! We also have a small population in NY state that is not well documented, and I recently came up with an odd population of pursewebs that also seems to lack prior documentation. I would love to send him some photos as well- how do you get in touch?