For Ozyptila praticola, The Allure Of Tree Trunk Moss May Evaporate With Its Moisture Content

Map of places where Ozyptila praticola has been confirmed
with a mature specimen. Squares, pins, crosses, and circles show
were O. praticola was collected in moss, cones, litter, and
cardboard live traps, respectively.

Tree trunk moss has turned out to be an excellent microhabitat in which to find the introduced crab spider Ozyptila praticola, just as I'd hoped. I began sifting riparian tree trunk moss in early May in my ongoing effort to determine the local distribution of O. praticola in western Washington. In the short time since, I've documented the presence of O. praticola at points along the Puyallup and White rivers, and along entire stretches of the Tolt, Snoqualmie, Cedar, and Green rivers. These new moss-derived records constitute extensions of the known local range of O. praticola in Washington state.

In addition to distribution information, the moss samples also provided a glimpse into the life history of O. praticola. The following observations are based on moss samples I took at sites that I have since confirmed are within O. praticola's local range. In May, I sifted moss at eleven sites and found adult females present at six of them (54% of sites). Adult males were also present in the moss at five of those six sites, but not at any of the other sites. In June, I sampled nine sites and found females at five (55% of sites), but found no males whatsoever. In July I sampled 7 sites and found females at only two of them (29% of sites), and again no males. Significantly, I didn't find any females after July 5th. The number of O. praticola juveniles present also fell dramatically in July to at most a few per site, whereas dozens were often present in May and June samples.

Average monthly temperatures and
rainfall for Seattle, Washington (USA).
Source

The tree trunk moss microhabitat became noticeably drier during the months I sampled. In May, moss was well hydrated and frequently damp to the touch. By mid-July, with the occasional exception of moss low on the trunk and shielded from desiccating conditions by understory vegetation, the moss was often dry enough to pulverize. This trend generally corresponded to the increasing temperatures and decreasing monthly rainfall totals typical for the region during that time of year (see chart, right). Whether seasonal desiccation of the tree trunk moss microhabitat was a contributing factor to the decreasing occurrence of O. praticola that I observed is unknown.

Xysticus pretiosus female with egg sac,
sifted together from tree trunk moss

Presumably, O. praticola was using tree trunk moss as, among other things, a place to mate and deposit egg sacs. However, I never found a female O. praticola with an egg sac in the sifted material, nor did I find any unattended egg sacs. This was in contrast to female Xysticus pretiosis I frequently sifted from the same moss. Female X. pretiosis that I collected in late June and early July usually managed to hang on to their egg sacs through the moss collection and sifting process, and continued guarding them on the sifting cloth. Perhaps any O. praticola egg sacs present were too firmly attached to the moss to be dislodged during sifting, or had been deposited somewhere other than on the moss.

Although I've spent the past few months concentrating my efforts on moss sifting, I still continue to tap fallen cones when the opportunity arises. Where fallen cones are available, tapping them is a quick and convenient way of searching for Ozyptila praticola, I have found. Although the moss and fallen cone microhabitats are quite different and hardly overlap spatially, it is interesting to compare my two data sets from a phenological point of view.

Looking at a chart of average monthly concentrations of male and female O. praticola in cones (data from a total of almost 4,300 cones tapped from 78 sites), I note two things. First, both males and females decrease in concentration from May through July, similar to the occurrence pattern I observed in tree trunk moss. (Where do the surviving O. praticola that leave the fallen cone and tree trunk moss microhabitats go during the summer months?) Second, O. praticola males reach their highest concentrations in fallen cones in April. If the occurrence of O. praticola males also peaks in April in tree trunk moss, then I missed observing that because I didn't start sifting moss until May. I'll need to adjust my moss sampling schedule next year to learn more.

Every method has its limits, and riparian tree trunk moss is no exception. With mature O. praticola apparently abandoning the microhabitat during the dry season, it looks like I may have to wait until autumn rains resume to continue this mode of sampling.

Photos Of Female Ozyptila praticola With Egg Sac

Female Ozyptila praticola in repose,
with egg sac.

I've finally seen an Ozyptila praticola female with her egg sac! I've been so focused on determining the local range of this introduced European species in Washington state (USA), that I haven't spent much time delving into its life history. So for me, this was a first.

I found her in a cardboard live trap that I had placed in Kirkland, Washington back on 29 March 2018. The trap was a roll of 12" by 3" single-face flute-A corrugated cardboard placed under a layer of pine needles in a dry, shrubby area at Jasper's Dog Park. I returned this week to check the trap and found it inhabited only by the O. praticola, her egg sac, and a few earwigs.

Female Ozyptila praticola protecting
her egg sac

The egg sac was lenticular in shape and apparently "tacked" to the cardboard substrate at intervals with silk. The female was in repose on one side of the egg sac when I opened the trap. However, after I began to move the trap this way and that to get enough light for photos, she became active enough to take a more protective position over the egg sac.

If you're interested in this species, you should also check out Tone Killick's excellent photos of a female O. praticola and her egg sac, taken near Gloucester, England.

Ozyptila praticola In Tree Trunk Moss On The Cedar River

Site location map. Pins and circles indicate moss and cardboard
trap samples, respectively. Blue, yellow and red markers
indicate adult O. praticola, juvenile O. ?praticola, and no
O. praticola found, respectively.

My ongoing search for the outer edges of the local range of the introduced European spider Ozyptila praticola (Thomisidae) brought me recently to the Cedar River. This spring, I set out cardboard live traps at five locations along the Cedar River between 154th Place SE in Renton and Landsburg Road in Ravensdale, and later collected juvenile Ozyptila probably-praticola from traps at two of them. To confirm which species of Ozyptila was present, I re-set traps or sifted tree trunk moss at thirteen river valley sites between the Interstate 405 overpass in Renton and Landsburg Road in Ravensdale. Logistical constraints dictated which collection method I used.

Female Ozyptila praticola sifted from
tree trunk moss at Habenicht Park

To date, I have found mature O. praticola from the I-405 overpass to as far upstream as Fred V. Habenicht Rotary Park in Maple Valley (blue icons on map, above). Upstream of Habenicht Park, the only mature Ozyptila I've collected were the native O. pacifica. Notably, I didn't find O. pacifica at Habenicht Park or any site downstream from there. As I've mentioned before, I've never found the native O. pacifica and the introduced O. praticola present at the same location.

29-May-2018 East Wenatchee and Culver Gulch, Washington

Site location map. Click to enlarge.

Two gridspaces in one day! Were we crazy to attempt such a mission, which also required over 300 miles of driving? I am happy to report that it was completely doable because we had a 10-15 species head start in both gridspaces (the goal is 21 or more). In addition, Rod Crawford had selected sampling sites that were so easy to access that we could dedicate all of our non-driving time to collecting. I never even had to put on my hiking boots. And so we made our first trip of the year over Snoqualmie Pass into eastern Washington to collect at Kirby Billingsley Hydro Park in East Wenatchee, and Culver Gulch, which is the site of the ghost town of Blewett.

Hydro Park

Location of Hydro Park.

Swamped picnic table and shore

The partial sample from this gridspace had come from a commercial fruit orchard, so Rod chose a collecting site that should provide a complementary suite of species. Hydro Park seemed just the ticket, with riparian habitats, buildings to collect house spiders from, and even some pine trees where I could tap fallen cones.

Female Phidippus audax from fence

Female Theridion murarium.
Copyright Rod Crawford

As it turned out, some of the riparian habitats were damaged or unavailable due to very high river levels. In addition, the interior of the bathroom building had recently been painted and was completely spider-free. Still, we were able to collect 16 species, only two of which duplicated previous records. I picked at least six identifiable species from fences, signs and building exteriors including the eastern U.S. transplant Phidippus audax (Salticidae) and the native but seldom collected Theridion murarium (Theridiidae).

Plenty of insects in lawn cones,
but no spiders

Rod spotted some Scots pine (Pinus sylvestris) cones that had fallen on the lawn. I wasn't going to bother tapping them, since cones on lawn tend to be spider-free. But I decided to take a look after all, since I was waiting for Rod to finish sifting litter anyway. And for all I knew, lawn cones might be more spider-friendly in eastern Washington! Nope. I gave up after 25 cones since the only thing they contained was insects. Oodles and oodles of insects.

Good cone source at
eastern park entrance

Fallen cone microhabitat

Luckily Rod's online trip-planning had revealed another cone tapping possibility at the other end of the park, and that one panned out. Small groups of pines (I'm uncertain of the species) had been planted on either side of the eastern park entrance, and cones and a thin layer of needle litter had been allowed to accumulate over the landscaping gravel used to surface the planting beds. The spider fauna wasn't rich, but it was present. I tapped 50 cones and collected 9 spiders from at least 6 species. Those identifiable were Bassaniana utahensis (Thomisidae), Theridion melanurum (Theridiidae), and Erigone aletris (Linyphiidae).

Culver Gulch

Location of Culver Gulch cone sites

Last July Rod and I collected spiders along Ruby Creek, a tributary of Peshastin Creek. Unfortunately the habitats were drier than we'd expected, and we fell a few species short of the minimum gridspace goal of 21. But that meant that this visit, we only needed to pick up a few species to put us over the top. It was very doable.

Fallen cones in an old gold
rush town...

...held these silver-sided beauties
(Euryopis formosa)

We stopped along SR-97 at the historical marker for Blewett, a former mining town situated near the confluence of Culver Gulch and Peshastin Creek. There were numerous fully open Douglas-fir (Pseudotsuga menziesii) cones on the dry and dusty ground at the edge of the parking area, so I got right to tapping. Almost immediately I found my old heartthrob, the beautiful "pine cone spider" Euryopis formosa (Theridiidae). As usual, we didn't find the species in any other microhabitat there. In total I collected 7 spiders and 3 identifiable species (Dipoena sp. #1 and Micaria pulicaria were the other two) from a set of 50 cones.

Cones among blooming
lupines

Stamping mill ruins

Next I crossed SR-97 to check out the cone tapping possibilities under a small ponderosa pine (P. ponderosa) that Rod had spotted. It was too small, unfortunately, to produce cones, but it did lead me to another lovely set of open Douglas-fir cones (not to mention the ruins of the old Blewett stamping mill!). I tapped 50 cones there and got nothing but E. formosa, 2 males and 13 juveniles. The E. formosa type specimen was collected in Bear, Idaho by the mining engineer Leslie Maurice Cockerell. I wonder if any of Blewett's miners ever noticed the creature with the precious metal sheen living amongst them.

Yellow-bellied marmots (Marmota flaviventris) picnicking on the lawn at Hydro Park.

14-May-2018 Van Zandt, Washington

Site location map. Click to enlarge.

Rod Crawford still has several gridspaces in Whatcom County that he wants to sample that are also of interest to me in my search for the introduced thomisid, Ozyptila praticola. With this dual purpose in mind, we spent the day collecting in the vicinity of Van Zandt, Washington. I've already found O. praticola in Bellingham and, most recently, in Lynden. However, neither of us turned up any in recent visits to nearby Nugents Corner or Everson, so I had no particular expectations for what we might find this day.

Cemetery cone source in the distance

The fallen cone microhabitat

We started the day at the Van Zandt Cemetery, where I quickly homed in on a batch of fallen cones dropped by a huge Douglas-fir (Pseudotsuga menziesii) tree in the cemetery's back corner. I tapped 61 cones and got only two spiders, but both were identifiable: a female Micaria pulicaria (Gnaphosidae) and a juvenile Bassaniana utahensis (Thomisidae).

Molting Platnickina tincta

Mating Platnickina tincta

The top rail of the cemetery's chain link fence was already uncomfortably hot to the touch by the time I started perusing it, but that didn't stop numerous spiders from using it. Salticus scenicus (Salticidae) were especially noticeable running along the rails, as well as darting in and out of the narrow gaps between rails and the rail sleeves that connect rail pipes end-to-end. But the most exciting rail-running salticid I found was a male Synageles. Synageles has been collected only twice before in Washington, once by me during the Roy BioBlitz in 2009. It is so rare and was so long ago that I had totally forgotten about it until Rod reminded me. He posted a nice photo of one of the spiders from Roy here. The underside of the fence rails was also a busy realm, especially for the theridiid Platnickina tincta (Theridion tinctum). Individuals of this species were using the space to both molt and mate.

Rod sifting litter near one of my
moss source trees

Male Callobius pictus 

From there we moved on to Hard Scrabble Creek Gulch, an invitingly shady oasis on what was turning out to be quite a hot day. While Rod sifted litter, I sifted moss, then sifted more moss. The usual denizens were present, although I found no Ozyptila of any species. Though I'm pretty new to moss sifting, I've quickly learned that when I remove a slab of moss from a tree trunk and see that I've broken through a quarter-sized tunnel, I should keep a lookout for Callobius (Amaurobiidae) making a fast break from my sifting cloth. They can really move, especially on a hot day like this!

Lush riparian vegetation

Piggyback plant (Tolmiea menziesii)
blooming by creek

By this time I was not only hot but also feeling grimy from all the spores, pollen and other dusty stuff that billows out of dry moss when you harvest and sift it. Sweeping riparian vegetation and looking for spiders in aerial webs next to a babbling Hard Scrabble Creek proved to be just what I needed. Feeling refreshed, I collected riparian tree trunk moss and had one more sifting session before calling it a day.

Oops, left in the field too long

Headstone a handy height
for labeling samples

On the way home, Rod and I stopped briefly in Bryant and Arlington to pick up some cardboard live traps that I hadn't been able to retrieve as soon as I would have liked. Having been in place for over a month, and made of thin, single-sided cardboard, they were a little the worse for wear thanks to local gastropods. But the real disappointment came when I opened them and dozens upon dozens of baby earwigs (Order Dermaptera) tumbled out. Every channel was crammed with them. The only spider daring to enter one of these earwig nurseries was a Salticus scenicus, which had sensibly sequestered itself in a silken retreat.

These horses near the cemetery studiously looked away whenever
I got out the camera, but otherwise watched everything we did.

7-May-2018 Alpha, Washington

Site location map. Chehalis locality not shown.

Rod Crawford was really pining for a field day in Lewis County, which meant a lot of driving for me. But the weather was favorable and the daylight hours long, so I agreed. After all, how could I resist a destination called Alpha? Our primary sampling sites were working forests west of Alpha on Centralia-Alpha Road, including a recent clearcut in a Douglas-fir (Pseudotsuga menziesii) and alder (Alnus sp.) woods and a second-growth woods dominated by western hemlock (Tsuga heterophylla).

The underside of a dew-bejeweled
agelenid web

Tiny linyphiid web in mud
crack

Morning dew was still very heavy on roadside vegetation, making it easy to spot the webs of certain agelenids and linyphiids. But where the sun hit dry ground, lycosids did abound! After an initial perusal of the dewy and the dry, I spent most of my day sifting moss gathered from tree trunks in the two forest types. I was, of course, most interested in seeing which species of Ozyptila was present. I only found juveniles, but they didn't appear to be O. praticola. Rod collected the only mature Ozyptila for the day, a male O. pacifica from leaf litter.

Neighbor's tree generously
provided...

...fallen cones full of surprises.

It wasn't until we moved on to the Alpha Cemetery that we found any cones for me to tap. A set of 50 Douglas-fir cones lying in landscaping debris just outside the cemetery's back fence produced zero spiders, but I had more luck with the 25 black pine (Pinus nigra) cones that had fallen into the cemetery from the neighbor's tree. They only contained two spiders, but both were the introduced species Zodarion rubidum (Zodariidae)! I first discovered this species in Washington in 2015. And oddly, with the exception of a few specimens found by another collector recently in tree litter and rotten wood near Husum, all of our Zodarion specimens in Washington have been found by me in fallen conifer cones (see map below).

A long line of shore pine ringed the
shuttered building

Cones were as vacant as the
building they surrounded

We made a final stop in Chehalis at a shuttered business near the airport so that I could have one more crack at tapping fallen cones. Here, finally, was a plentiful deposit of cones! And they were the native shore pine (Pinus contorta var contorta), too. But 50 cones produced only one juvenile dictynid. Still, having found Zodarion at the cemetery, I couldn't be too disappointed in the cone-tapping aspect of the day.

Be sure to read Rod's account of the day, too!

Location of Zodarion rubidum found in Washington state. Blue and yellow
pins indicate mature and juvenile specimens, respectively

Ozyptila praticola In Tree Trunk Moss On The Tolt River

Site location map. Pin and squares indicate cone and moss
samples, respectively. Blue, yellow and red markers indicate
adult O. praticola, juvenile O. ?praticola, or no O. ?praticola
found, respectively.

Since learning a few months ago that the European crab spider Ozyptila praticola  (Thomisidae) can be found in tree trunk moss, I've been working my way up a few river valleys, sifting moss, in my ongoing search for the edges of O. praticola's local range. I just completed one such river series along Tolt River. Tolt River is a tributary to the Snoqualmie River, and runs along the southern edge of Carnation, Washington in King County.

Artifacts indicate past land
use as home sites.

I visited three Tolt River sites on 12 May, then an additional three sites on 18 May. The sites spanned a distance of approximately 5.3 river miles (squares on map, above). The stretch of the river valley I sampled is lightly peppered with currently occupied homes interspersed with former home sites that are being restored as part of the Tolt River Natural Area salmon habitat protection initiative. As far as I could determine from historical aerial photos on Google Earth, many of my sample sites had homes on them as recently as three to seven years ago.

I had tapped O. praticola from cones in Carnation in 2016 (blue pin in map above), so I knew that the species was in the neighborhood. But I didn't know if it had spread into the more natural habitats found along the Tolt River. Rod Crawford didn't find any O. praticola in 2009 when he collected spiders on the west side of Snoqualmie River at Tolt River–John MacDonald Memorial Park.

From parking lot, a view through a
strip of riparian forest to the Tolt River.

Male O. praticola sifted from
tree trunk moss at first site.

My first, most downstream site was located in a wooded riverside parking area near where Route 203 crosses Tolt River. I sifted about a sweep net full of moss from the trunks of black cottonwood (Populus trichocarpa) and bigleaf maple (Acer macrophyllum) and collected 1 female, 2 male and 40 juvenile O. praticola. Ozyptila praticola was by far the most numerous species present in the sample.

Mossy riparian cottonwoods at third
site, where a home formerly stood.

Male O. praticola sifted from
tree trunk moss at third site

The moss I sifted at the next site upstream produced a dozen juvenile O. probably-praticola, but no adults. Moss at the third site, however, mirrored the first in producing 2 female, 2 male, and 20 juvenile O. praticola.

Mossy maple at final up-
stream site.

Female O. praticola sifted from
tree trunk moss at most upstream
site.

Although young thomisids were present at the fourth and fifth sites, I didn't find any spiders that I could with any confidence identify as O. praticola. But at the final, most upstream site, I sifted 1 female and 2 juvenile O. praticola from moss I harvested from bigleaf maple and black cottonwood trunks.

Clearly, O. praticola is present along the Tolt River for at least the first 5.3 river miles from its confluence with Snoqualmie River. This finding then raises the question, has it spread even farther upstream? If the species is simply following the riparian forest upstream, it seems reasonable to anticipate that it may have spread even farther upstream than where I stopped sampling. However, if it is present at these sampling sites only because it was inadvertently introduced by former homeowners, then it may not have spread upstream beyond the homesteaded areas much if at all. The only way to know for sure is to continue sampling farther upstream. But unfortunately, road access is restricted farther upstream. Anyone have a canoe?

The effort to revegetate former housing sites is under way.