Saturday, October 24, 2015

22-Oct-2015 Marysville and Arlington, Washington

Site location map. Click to enlarge.
Last week I looked for but did not find the introduced crab spider Ozyptila praticola (Thomisidae) at two sites on the south end of Tulalip and Marysville.  But spiders are patchy even in microhabitats they're known to frequent, so a few negative results could mean that the species isn't present in the area, but not necessarily.  It could also mean that the sampling wasn't intensive or extensive enough to detect them.  With these possibilities in mind, I returned to Marysville for another cone sample and then headed further north to Arlington to continue my search for O. praticola.


Marysville collection site
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My first stop was the parking lot behind the Marysville Municipal Court, which features a dumpster corral flanked by cypresses and backed by black pines (Pinus nigra).  Several hundred cones lay on a bed of pine needles.  I tapped 100, most of them lying near or under the drip line of the cypresses.  The result was 13 spiders and 3 species, plus 7 harvestmen.

Tegenaria sp. in black pine cone
Pelegrina sp. juvenile
The introduced linyphiid Tenuiphantes tenuis was the most abundant species present, with Tegenaria sp. (Agelenidae) coming in a close second.  The most spectacular spider both in life and in my wet vial was a penultimate male Pelegrina sp. (Salticidae), which turned bright red in alcohol.  I found no O. praticola.


Haller Park cone source
Pine cone microhabitat in Haller Park
Next I headed north to Arlington.  My first stop was Haller Park, situated at the confluence of the north and south forks of the Stillaguamish rivers.  A youngish western white pine (Pinus monticola) growing along the Centennial Trail, an old railroad right-of-way bisecting the park, had dropped cones on the steep grassy embankment.  I could find only 13 cones to tap, and they produced two juvenile spiders: a penultimate female Clubiona sp. (Clubionidae) and a Tegenaria sp. (Agelenidae).  No O. praticola.

Pines at Snohomish Co. District Court
Fallen cone microhabitat at the
SnoCo District Court in Arlington
Not satisfied with the measly 13 cones I found at the park, I cruised through town until I spotted this row of Scots pines (Pinus sylvestris) planted behind the Snohomish County District Court building.  Tapping 50 cones I collected 6 juvenile spiders, all apparently of the same species: Enoplognatha probably ovata (Theridiidae).  No O. praticola.

Clubiona sp. from Haller Park cone
Returning to Seattle, I tapped 15 P. nigra cones from the same accumulation I described in May.  Mainly it was to verify that adult O. praticola were still "on the hoof".  Indeed they were.  That small number of cones produced 4 O. praticola in total: 1 female, 1 male, and 2 juveniles.  So I can't attribute to seasonality my not (yet?) finding any O. praticola north of Everett and the Snohomish River.

View up South Fork Stillaguamish River from the Centennial Trail in Arlington

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