Tuesday, May 24, 2016

20-May-2016 Rock Island Creek, Washington

Site location map. Click to enlarge
Across the Columbia River from Wenatchee looms Badger Mountain, a part of the Columbia Plateau towering up to 1,000 meters above the city at its feet.  Much of Badger Mountain has been converted to agricultural use, but some areas of native shrub-steppe vegetation remain, as does an outlier population of ponderosa pines (Pinus ponderosa).  I tapped ponderosa cones once before on Badger Mountain, on 1 May 2009.  On that day I collected 3 species: Euryopis formosa (Theridiidae), Pholcophora americana (Pholcidae) and Xysticus locuples (Thomisidae). Would I find anything different a few miles to the south on this day almost exactly 7 years later?

View of riparian vegetation from the
shrub-steppe zone
Rod Crawford navigated us to the upper reaches of Rock Island Creek, where I was in cone tapping heaven.  There were ponderosas in the riparian zone, ponderosas in the sagebrush on the hillside above the riparian zone, and ponderosas straddling both habitats, providing me with an opportunity to tap cones that had fallen onto a variety of substrates.

Road Cones

Road cones and their source
The road cone microhabitat
I decided to sample the easiest set of cones first: those dropped onto the dirt road by a ponderosa growing in the riparian zone.   I tapped 50 cones and collected 14 spiders from 8 families.  Not bad for some dusty cones!  All the spiders were juvenile, with Anyphaena sp. (Anyphaenidae) being the most numerous, but Rod was able to identify Bassaniana utahensis (Thomisidae) and Poecilochroa columbiana (Gnaphosidae).

Riparian Cones

Source of riparian cones
Fallen cones in lush riparian zone
Next I hiked up the head of a very short tributary, which appeared to be spring fed.  A mature ponderosa growing beside the tiny headwater stream had dropped cones in the riparian zone.   From 50 tapped cones I collected only 7 spiders, but three species were identifiable.  These included the most common "pine cone spider" Euryopis formosa (Theridiidae), Dictyna uintana (Dictynidae) and a Pocadicnemis (Linyphiidae) still to be identified.

Near-Riparian Cones

Source of near-riparian cones. Note
chaparral on up-slope side of tree
Cones on thick bed of needle litter
My next set of cones had fallen beneath a ponderosa pine whose drip line straddled the riparian and sagebrush zones.  I again tapped the usual 50 fallen cones and collected 13 spiders from 7 families and 3 species: Anyphaena pacifica, B. utahensis and the second-most common "pine cone spider" Pholcophora americana (Pholcidae).

Hillside cones

Hillside cones & lupine
Hillside cone source
The final 50 cones I tapped had fallen from a ponderosa pine growing up-slope from the near-riparian pine.  Here the surroundings were classic shrub-steppe vegetation: Artemisia tridentata, Lupinus, Balsamorhiza, Ribes, etc.  From these 50 cones I collected moths, beetles and a lovely lilac-colored caterpillar, but only 1 spider, a juvenile E. formosa.

Searching out and tapping these 200 cones took up most of my sampling time, but it also added 4 species to the site list.

Female Psilochorus herperus
with egg sac
The eye arrangement on this
under-rock exuvium says lycosid
After tapping all those cones I was happy to assist Rod in a little rock turning.  Almost immediately I found a female Psilochorus hesperus (Pholcidae) carrying her egg sac in her chelicerae.  And then I found another, and another, and another...  Intriguingly, the rock pile I was examining was only 5 or 6 feet from the pile Rod was looking at, yet he found no P. hersperus there.  It makes me wonder whether this species is somewhat colonial.

Be sure to read Rod's account here!

Tiger beetle tapped from fallen ponderosa pine cone

In the headwaters of Rock Island Creek...

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