Cardboard Live Traps Extend Known Range Of Ozyptila praticola In Washington

Map of cardboard live trap sites deployed 11-Feb-2018
between Monroe and Gold Bar, Washington.

Until quite recently, I have been able to investigate the local range of the introduced European crab spider Ozyptila praticola (Thomisidae) as a part of my ongoing survey of the fallen conifer cone microhabitat in western Washington. This is because O. praticola uses the fallen cone microhabitat when it is available. Unfortunately, the fallen cone microhabitat isn't always available in places I want to search for O. praticola. This has become problematic as I seek to fine-tune my understanding of the current boundaries of O. praticola's local range.

To remedy this, I have started sampling additional microhabitats that I know O. praticola can be found in, including moss and litter. While this has been useful in specific localities, as with fallen cones neither of these microhabitats is reliably present or accessible in all of the places I wish to sample. In response to this situation, I created cardboard live traps, an artificial microhabitat that, theoretically, I can deploy along sampling transects virtually anywhere.

March, 2018 temperature history for Monroe, Washington. Graph modified
from Wunderground. The orange line represents the 50 F (10 C) isotherm.
Click to enlarge.

I deployed my first transect of live traps along the U.S. Hwy 2 corridor between Monroe and Gold Bar, Washington, on 11 Feb. 2018. I then waited until daytime temperatures peaked above 50 degrees Fahrenheit (10 Celsius) and nighttime lows remained above freezing for several consecutive days before checking the traps for spiders. I chose those parameters under the assumption that overwintering O. praticola would become mobile enough to start entering my traps under those conditions. But it was all guesswork; I'm learning as I go.

Penultimate male Ozyptila praticola
in a cardboard live trap in Monroe,
Washington

I had deliberately anchored the western end of the transect in a particular locality in Monroe where I already knew O. praticola was present. My plan was to use the Monroe traps as a bellwether that O. praticola had indeed become active and thus it was worth my time to check rest of the traps in the transect. On 19 March, the 10th consecutive day of my prescribed weather conditions, I checked the traps in Monroe and found one penultimate male O. praticola in each. I considered this the "go" signal and proceeded to check the other traps in the transect.

This cardboard live trap at the base of
a Mahonia shrub in downtown Sultan
harbored a female O. praticola.

Traffic issues and time constraints prevented me from checking three of the traps (pink pins on the map, below), while some traps were missing entirely (white pins). Nevertheless, I was able to find and check enough traps between Monroe and Sultan to learn, by the presence of juvenile Ozyptila in them, that O. praticola was likely present in those localities (yellow pins). Further searching for adults would have been warranted in those places had I not also recovered a mature female O. praticola from a trap a bit further east, in downtown Sultan (blue pin). I found no Ozyptila in any trap east of downtown Sultan.

Transect results. See text for pin color code. Some pins removed for clarity.

This set of cardboard live traps helped refine our knowledge of the extent of O. praticola's local range. Prior to this experiment, Monroe was the eastern-most place along the U.S. Hwy 2 corridor where I had confirmed the presence of O. praticola with a mature specimen. It is now clear that O. praticola is present at least as far east as downtown Sultan.