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.

16-Mar-2018 Stanwood, Washington

Site location map. Click to enlarge.

I'd had my eye on Stanwood for some time as a place to search for the introduced crab spider Ozyptila praticola. This is because Stanwood was the only remaining urban area between Seattle and Bellingham that I hadn't yet sampled. This sunny, warmish day turned out to be the day! In all, I tapped fallen conifer cones at four Stanwood sites.

Scots pine cone and owl
pellet full of rodent bones

Rodent skull in owl pellet

For my first sample I tapped 100 fallen Scots pine (Pinus sylvestris) cones near Heritage Park and collected 20 spiders. The sample contained at least 6 species, but only one was mature and identifiable: a female Tachygyna vancouverana (Linyphiidae). The most common spider in the sample, however, was Enoplognatha probably-ovata (Theridiidae), of which there were 13 juveniles present. If this spider sample was a bit ho-hum, the sampling location was not. This was on account of the ground beneath the trees being littered with owl pellets! At least one pellet contained a visible rodent skull.

Lonely parking lot pine

Lots of cones, few spiders

I found my next cone source in the parking lot of a restaurant on Route 532, the city's main thoroughfare. A lone black pine (P. nigra) was growing in a small patch of soil surrounded by blacktop and concrete -- not a particularly promising site. However, fallen cones and needle litter had been allowed to accumulate, so I decided to go ahead and sample. Fifty tapped cones produced only 2 spiders: another female T. vancouverana and another juvenile E. probably-ovata.

This row of Douglas-firs...

...provided lots of open cones

If that last sample was disappointing, the next one, taken at the Stanwood Cemetery, was the most diverse of the day. A row of Douglas-firs (Pseudotsuga menziesii) planted along a section of the back fence provided a multitude of open cones. I tapped 50 cones and collected 24 spiders and at least 7 species, six of which were immediately identifiable. These included the linyphiids Erigone aletris, Grammonota kincaidi, Neriene digna, and yet more T. vancouverana. Also present were several juvenile Platnickina tincta (Theridiidae) and a penultimate male Philodromus dispar (Philodromidae). All in all, a typical urban sample for this part of the state.

Church Creek Park

My final sampling location was the wooded Church Creek Park, where I tapped more Douglas-fir cones and also sifted a batch of moss collected from bigleaf maple (Acer macrophyllum) trunks and logs. The cones produced only 7 spiders from 3 species already collected this day, including the two present at each of the four sampling sites: T. vancouverana and E. probably-ovata.

Ozyptila praticola was absent from all four of the cone samples. And while I haven't yet ID'd the moss spiders, there were no crab spiders in that sample, either. If O. praticola is present in Stanwood, it is too localized or at too low a density to be detected by my sampling methods.

Female Neriene digna tapped from fallen Douglas-fir
cones in Stanwood Cemetery

Ozyptila praticola Found In Tree Trunk Moss

Deliciously shaggy moss on
alder trunks, Cultus Mtn.

Last week, while collecting spiders with Rod Crawford on Cultus Mountain (Skagit County), I decided to sift some of the luxuriant moss growing on the trunks of alder trees there. One of the spiders I found therein was a male Ozyptila pacifica, a native thomisid. This caught my attention because I had found a female O. pacifica in cascara tree trunk moss near Vader (Lewis County) the previous spring, which happened to be the only other time I had ever sifted tree trunk moss.

Readers of this blog will know that I've used a variety of sampling methods in my search for the introduced thomisid Ozyptila praticola in western Washington. These include tapping fallen conifer cones, sifting leaf litter, placing pitfall traps, and deploying various types of cardboard live traps in shrubs and on tree trunks. But it wasn't until finding that male O. pacifica last week that it occurred to me to search for O. praticola in nature's ready-made live trap: tree trunk moss. Tree trunk moss isn't common in the urban areas I've been searching for O. praticola, but it can sometimes be found in protected pockets of forested parkland, especially near streams. If O. praticola also uses tree trunk moss, I'd have an additional tool in my praticola search toolbox. Time to sample tree trunk moss in the O. praticola zone!

Thin moss on alder trunks
was nearly uncollectable

Knowing that O. praticola is common along a certain stretch of the Burke-Gilman Trail in Seattle (King County), I grabbed my sifting gear and hiked towards a stretch of the trail that traversed a forested slope. The first place I looked was an unnamed wooded draw up-slope from the trail. I found several alder trees that had moss growing on their trunks, but the moss layer was so thin that it was impossible in most places to remove from the bark. The tiny bits of moss I was able to harvest held no Ozyptila, but many tiny theridiids.

Moss on maple trunk thick
enough to harbor O. praticola

From there I crossed the trail and made my way down to the base of the slope to a small creek, a 35 meter drop in elevation. That's where I found what I was looking for: next to the creek stood a bigleaf maple that had a one to two inch thick cushion of moss growing on the side facing the creek. I was only able to collect a few handfuls, but even so that modest volume held two female and several juvenile O. praticola. I sifted a second double handful of moss removed from a nearby log, and again found a female and several juvenile O. praticola.

What I didn't find was any O. pacifica, even though Seattle is theoretically in O. pacifica's range. In fact, I've never found O. pacifica in any place where O. praticola is present. Whether this is due to the presence of O. praticola per se or to other factors is an unanswered question.

Female O. praticola found in moss

Thinking back to the European reports I've read about O. praticola being found under cardboard placed on tree trunks, it makes sense that the species would also utilize tree trunk moss in places where it is available. However, I've never seen mention of this in any published source. Rod Crawford tells me that this is the first observation he is aware of of O. praticola in Washington using the tree trunk moss microhabitat. In any case, it looks like it will be worth my time to sift moss when I'm out looking for O. praticola.

Moss, lovely moss