Sunday, March 18, 2018

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

Monday, March 12, 2018

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

Thursday, January 25, 2018

Read Our Paper About First Pseudueophrys lanigera Records In North America

Female Pseudeuophrys lanigera on
building exterior in Seattle, Washington
Readers of this blog will recall that in 2015 I discovered the European jumping spider Pseudeuophrys lanigera in some fallen pine cones in Mukilteo, Washington (Snohomish County). This constituted the first record of the species in North America. Subsequently I and others found more specimens in the Washington cities of Seattle (King County) and Bremerton (Kitsap County). Rod Crawford and I summarized these findings in a paper in Pan-Pacific Entomologist which can be accessed here free of charge.

Tuesday, January 16, 2018

Spider Traps Made Of Corrugated Plastic Perform Poorly In Wet Weather

Shortly after the New Year, I deployed another set of spider traps in the woods near my house in Seattle, Washington (USA). I had a number of questions I hoped these traps would answer about the introduced crab spider Ozyptila praticola (Thomisidae), including:
  • Will O. praticola use traps made from corrugated plastic?
  • Will O. praticola use traps made of rolled-up single-sided cardboard (the easiest trap to make)?
  • Does the orientation (vertical, horizontal) of the corrugated channels make a difference?

Corrugated cardboard and plastic
"stack" traps
Corrugated cardboard "roll" traps
I had recently found that small stacks of flute B cardboard placed in the crotches of shrubs work very well as O. praticola traps. Therefore, I made another set of these "stack" traps as a control. Next, I made a plastic version of the control traps, using corrugated plastic instead of cardboard. And finally, I rolled strips of single-face flute A cardboard into cylinders to make "roll" traps. This is the same material that I used previously for tree trunk bands. On 4-Jan I set out five cardboard stack traps, five plastic stack traps, and ten roll traps, each in the crotch of a different shrub. On 15-Jan, I checked the traps for spiders. 

Films of water formed inside the
channels of the plastic traps
Much to my surprise, the plastic stack traps were almost entirely devoid of spiders. The reason, it seemed, was that a film of water was blocking the bottom end of many of the corrugated channels. This was true even though no rain had fallen in over two days. Water droplets also adhered to the inner walls of many channels. I had considered the propensity of cardboard to absorb water to be a potential problem here in rainy Seattle, but it appears to actually be a positive attribute of the material in so far as it prevents water droplets and films from forming. I will re-test the corrugated plastic traps again this summer, during the dry season. However, they are clearly unsuitable for use during wet weather.

The cardboard stacks again performed well; each contained at least one O. praticola. In contrast, only six of the ten cardboard rolls contained any O. praticola. There was no correlation between the orientation of the corrugated channels and the presence of O. praticola within.

Even though the roll traps didn't perform as well as the stacks, they may be the best trap to use in summer because they will be much easier to extract spiders from. The layers of the single-face cardboard I use to make roll traps are easily separated regardless of whether they are wet or dry. But the layers of the double-face cardboard used to make stack traps only separate cleanly when the cardboard is damp. Summers in western Washington are dry, not damp.

Snails like my traps, too.
Although the traps had only been in the field for 11 days, gastropods had started to seriously degrade the outermost layer of some of the roll traps. The problem wasn't as serious with the stack traps because they were made with thicker face paper. In future, I'll put a band of box tape around the entire circumference of each roll trap to help protect it from grazing slugs and snails.

Monday, January 8, 2018

7-Jan-2018 Spanaway, Washington

Site location map. Click to enlarge.
Blue pins: Ozyptila praticola confirmed via adult specimen.
Red pins: No O. praticola adults or ?praticola juveniles found.
One of the benefits of tapping fallen conifer cones is that they usually aren't too wet to sample unless a soaking rain falls. Chances of afternoon rain were high in the Spanaway area on this day, but I didn't think that enough rain had fallen the night before to make cones too wet for some morning tapping. As luck would have it, I was right, and managed to tap cones at two sites before the predicted rain began to fall.


Young black pines along
the Walmart border
Fallen black pine and
Douglas-fir cones
In about the year 2001, a Walmart was built on the site of a former gravel pit in the south end of town. Subsequently, a double row of black pines (Pinus nigra) and Douglas-firs (Pseudotsuga menziesii) was planted along much of the property's northern and eastern borders. These trees are now large enough to produce cones, and I had no trouble finding 100 cones to tap. Although the cones' scales were only partially opened, they still produced 27 spiders and 5 identifiable species, mostly linyphiids. The most abundant species was Tachygyna vancouverana, with a total of 15 males and females.

Female Wubana pacifica
Wubana pacifica's white "butt spot"
Also present were two female Wubana pacifica, a species I've only tapped from cones once before but which I recognized immediately due to its white "butt spot".

Light rain was falling by the time I finished sampling at this location, so I delayed my lunch break and immediately began searching for another set of cones to tap. I hoped to complete one more sample before everything got too wet.

Power Substation

White pine at power substation
Lots of poorly-opened
white pine cones
Fortunately I found what I was looking for fairly quickly at a nearby power substation: a white pine tree (P. strobus or P. monticola) large enough to shelter me (and the fallen cones beneath) from the worst of the rain that was now falling in earnest. The cone scales were poorly opened here, too, but they were open far enough for small spiders. Still, I only found 3 spiders in the 50 cones I tapped, all T. vancouverana. I would have tapped an additional 50 cones, but the pouring rain brought my efforts to a halt.

I'm always curious to see whether I find the introduced European spider Ozyptila praticola at any given location. I didn't find any this day, or indeed in any of the other approximately two dozen sets of cones that I've tapped in Pierce County (see map above). If it's present in the county, it's highly localized.

It's that time of year...

Wednesday, January 3, 2018

7-Dec-2017 Mowich Road, Washington

Site location map. Click to enlarge
Rod Crawford and I had originally planned to sample east of Wilkeson along South Prairie Creek in Pierce County. But en route on the highway, something we ran over got stuck in the undercarriage and was dragging. Luckily, there happened to be a Jiffy Lube near our exit in Bonney Lake, and the folks there removed the "hitchhiker" for us (for free -- thanks, guys!). Since the road to South Prairie Creek was known to be quite rough, and we weren't sure of the condition of the undercarriage, we opted for an alternate trip plan that Rod had prepared. Our new destination became a stretch of Mowich Section Road (Rte 165) south of Carbonado.

Loose bark on fallen tree...
...harbored male Coriarachne
brunneipes, among others
Rod had carefully chosen the original and alternate sites because the region was experiencing a temperature inversion; both sites were high enough in elevation to be in warmer air than the lowlands, but not so high in elevation as to be snowbound. Or so we thought! As it turned out, any shaded ground was blanketed with snow. This meant that much of the forest understory would be unavailable for sampling. However, conifer foliage and sun-exposed roadside vegetation were dry, so we thoroughly sampled those microhabitats. In addition, Rod was able to find some cold but still productive alder litter, and I found a fallen tree suspended above snow level that had a variety of spiders beneath its sloughing bark.

Cone source was a dead tree
All cones were well opened
The snow created a problem for me in particular in that if there were any fallen cones, they were now buried. So I opted to tap the only cones available: Douglas-fir (Pseudotsuga menziesii) cones still attached to a dead tree. I picked and then tapped 34 cones and found one salticid exuvium and five juvenile spiders: two indeterminate salticids, one Cyclosa, one Araneus ?diadematus, and one Philodromus rufus. In other words, a typically arboreal sample.

You can read Rod's trip narrative here.

Oh no, snow!

Monday, January 1, 2018

Catching Ozyptila praticola In Non-lethal Cardboard Traps

3" x 3" flute B corrugated cardboard
stack spider trap in Mahonia sp.
Early in 2017 I decided to augment my cone-tapping efforts by deploying pitfall* traps. In theory, doing so should have made my ongoing search for the introduced European crab spider Ozyptila praticola (Thomisidae) more robust. My plan was to place pitfall traps in areas where fallen conifer cones weren't available, but where I still needed a sample.

I abandoned my pitfall plan after a few months, however, for two reasons. First, when I placed control pitfall traps in an area I knew to be rife with O. praticola, I didn't catch any. This was despite the fact that I'd placed the traps in April and May, months of peak male O. praticola activity (pitfall studies in Europe capture mostly male O. praticola). Secondly, I was getting a troubling amount of bycatch. Even as my pitfall traps failed to capture my target species, they did capture and kill amphibians, bumblebees, slugs and snails. I found this destruction of non-target species to be unethical and unacceptable.

5" x 5" flute B corrugated
cardboard stack spider trap
in Acer macrophyllum
In the mean time I'd been leafing through papers that mentioned O. praticola, and learned that the species is sometimes found on tree trunks in Europe. Among the many gizmos used to collect them on tree trunks, traps made of corrugated cardboard caught my attention. For example, Bogya (1999) found that O. praticola overwintered in or under corrugated cardboard bands placed on the lower trunks of pear and apple trees in an orchard in northeastern Hungary. The traps were placed "in autumn before leaf fall and were collected 2-2.5 months later, after the first frost." Machac & Tuf (2016) reported that in summer in the Czech Republic, pieces of cardboard on oak tree trunks were "inhabited mostly by females with egg sacs, e.g. Clubiona pallidulaNuctenea umbratica or Ozyptila praticola".

So here was another method of detecting O. praticola that was also non-lethal to other animals - yay! In addition, cardboard is inexpensive and compostable. I decided to conduct a pilot study to see whether cardboard traps were an effective way to capture O. praticola here in western Washington.

Single-face flute A (left) & double-face
flute B (right) cardboard used in traps
The first step was to decide which corrugation flute size to use, since my traps needed to have spaces large enough to accommodate adult female O. praticola. Oddly, almost none of the researchers using cardboard to trap spiders have reported the flute size they used. I decided to try both flute A and flute B. Flute A cardboard has a wavelength of 9 mm and a peak amplitude of 4 mm. Flute B is slightly smaller, having a wavelength of 8 mm and a peak amplitude of 3 mm. Most of the shipping boxes I found in recycling bins were made with smaller flute sizes, but with perseverance and Rod Crawford's help, I managed to find some nice pieces of clean discarded flute B cardboard. Flute A, however, was nowhere to be found. I ended up ordering a 250 foot roll of 3 inch, single-face flute A cardboard from an office supply store.

My plan was to do the following in my O. praticola control plot in Seattle:
  • Wrap a band of flute A cardboard around the trunks of ten trees, with the corrugated side facing the tree. Place the band 2 ft off the ground on five trees, and 5 ft off the ground on another five.
  • Place one six-layer stack of 3" x 3" flute B squares in the crotch of each of five shrubs. The bottom of the stack should be close to the top surface of the litter layer.
  • Place one six-layer stack of 5" x 5" flute B squares in the lowest crotch of each of five trees.
3" single-face flute A
corrugated cardboard band
spider trap on Acer saccharum
When making the cardboard stacks, I alternated the orientation of each square of cardboard so that its corrugated channels were perpendicular to the neighboring pieces. The stacks were held together with cotton string and placed "upright" in the shrub or tree so that half of the channels were vertical and half horizontal. On 25-Sept, while I waited for my roll of flute A to arrive, I made and deployed these flute B stacks. On 1-Oct I put up the tree trunk bands and also added two squares of flute A cardboard to each stack.

On 8-Oct I checked all bands and stacks for inhabitants. Most contained spiders, but none were O. praticola. I didn't check the traps again until the end of December (half on the 20th and the rest on the 30th), and by then both types of traps contained O. praticola. Raccoons had destroyed 5 tree trunk bands, but of the 5 remaining, one contained no O. praticola and the four that did contained a total of 6 females, 0 males, and 20 juveniles.

Close-up of a 3" single-face flute A
corrugated cardboard band
spider trap 
All five 3" x 3" stacks in shrub crotches survived intact, and each contained at least one mature O. praticola. Altogether, they contained 21 female, 1 male, and 125 juvenile O. praticola. I found adult females in the channels of both the flute A and the flute B pieces.

Of the 5" x 5" stacks in tree crotches, one had been removed and thrown to the ground by a raccoon, and contained no O. praticola. Of the four stacks remaining in place, only two contained adult O. praticola. In total, the four surviving stacks contained 3 female, 0 male, and 16 juvenile O. praticola.

This female Ozyptila praticola had been wintering inside
a corrugated cardboard band on a tree trunk
Apparently O. praticola had not yet climbed above the litter in search of overwintering sites when I checked the traps on 8-Oct, but had done so at some point in the following two months. Of the three trap permutations I tried, the 3" x 3" stack in shrub crotch was the clear winner for late fall trapping. Not only did every trap contain adult O. praticola, but the raccoons left them completely untouched. Once the weather warms up in spring and overwintering spiders become active again, however, I can't be certain which type of trap will provide the best odds of capturing O. praticola. Recall that European researchers have found female O. praticola in trunk traps in summer. Perhaps different traps will be ideal in different seasons. I guess I'll find out!

A note on removing spiders from cardboard traps: On 8-Oct, the traps were still fairly dry and so I could prod spiders out of the corrugated channels with a fine wire. However, by December the traps were wet from seasonal rain. This made the wire useless as a prod, since it got stuck in the softened channel walls. Therefore, the only way to remove the spiders was to completely destroy the traps by pulling apart the layers of the cardboard and shaking them into a sweep net. When planning different sampling methods, it could be worth bearing in mind that cardboard traps can be collected and processed even on rainy days. This can't always be said for litter sifting or other methods of collection.

Other spiders common in this set of cardboard traps included juvenile Cheiracanthium sp. and female Clubiona pallidula (both introduced species), female and male Tachygyna ursina and T. vancouverana, juvenile Philodromus sp., juvenile Phrurotimpus sp., and female Pelegrina aeneola and Phanias albeolus.

I still have a lot of work to do to determine which type of trap works best when, and how to raccoon-proof tree bands, but at least this pilot study serves as proof of concept.

*Simon Leather wrote an interesting and entertaining history of the pitfall trap, which can be found here.