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.

Walmart

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.

Thursday, December 14, 2017

14-Dec-2017 Hunts Point & Bellevue, Washington

Site location map.
Blue: O. praticola confirmed via adult specimen.
Yellow: Juvenile O. ?praticola found.
Red: No O. praticola adults or ?praticola juveniles found.
With a few hours free on this, the final day in an extended dry spell, I decided to cross Lake Washington to look for Ozyptila praticola (Thomisidae) in the Bellevue area. I was sure that Bellevue lay solidly in the heart of O. praticola's local range. However, since I've done very little sampling there, I had no specimen to validate my assumption.

Hunts Point

Black pines at Hunts Point
Town Hall
I exited Hwy 520 at 84th Ave because I had seen, via Google Street View, that that street was lined with black pine (Pinus nigra) trees. This was indeed the case, but unfortunately their litter and fallen cones had been removed. So I proceeded to the next possibility, which was another row of black pines next to the Hunts Point Town Hall. The litter there was intact, but the fallen cones were poorly opened. Nevertheless, they harbored enough spiders to let me know I was on the right track; tapping 50 cones got me 3 spiders, two of which were O. praticola juveniles.

Cone scales poorly opened,
but needle-wood chip litter...
...produced several adult O. praticola.
Having had success sifting pine litter in a similar situation the other day in Kent, I decided that sifting another batch here, where I knew O. praticola was present, was probably a better use of my very limited time than looking for another cone deposit that might (or might not) produce a mature specimen. This turned out to be a good decision; the bag of litter (pine needles and wood chip mulch) I sifted contained 6 O. praticola, including 3 females and 1 male. Hunts Point is a tiny town of just 500 inhabitants. There are probably more O. praticola there than people.

Bellevue

Black pines on Bel-Red Road...
...had nice thick needle litter beneath.
I was still hoping to take a sample in Bellevue proper, but had no time to scout out a good cone source. So I made do with sifting litter from beneath yet another row of black pine trees with closed fallen cones, this time along Bel-Red Road. My luck wasn't as good at this site, as I found only one juvenile O. praticola and had no time to sift a second batch.

A pine peeks over the town hall of Hunts Point, where O. praticola
undoubtedly outnumbers the human inhabitants.

Tuesday, December 12, 2017

12-Dec-2017 West Seattle, Washington

I tapped cones dropped by both pines
The fallen cone microhabitat
An appointment today in Seattle's industrial district put me so close to West Seattle that I couldn't resist buzzing over there to take a sample. Driving south on 35th Ave., I very quickly spotted two western white pines (Pinus monticola) that had dropped open, accessible cones in front of neighboring houses. If only every sampling site were so easy to find!

Female O. praticola tapped from cones
Penultimate male Xysticus ?cristatus
I tapped 50 cones and collected 8 spiders and 3 identifiable species: An erigonine to be identified later, Tachygyna vancouverana (Linyphiidae), and Ozyptila praticola (Thomisidae). I'm not at all surprised to find O. praticola in West Seattle, but I'm quite happy to have found a specimen to verify its presence in that quadrant of the city. Also present in this sample was a penultimate male Xysticus probably-cristatus (Thomisidae), another introduced crab spider that's become established in western Washington.

Site location map. Click to enlarge. West Seattle site is circled.
Blue: O. praticola confirmed via adult specimen.
Yellow: Juvenile O. ?praticola found.
Red: No O. praticola adults or ?praticola juveniles found.

11-Dec-2017 Kent Redux & Covington, Washington

Site location map. Click to enlarge.
Last week, when I found all those juvenile Ozyptila praticola (Thomisidae) in fallen pine cones in Kent, I knew that I should continue the search for a mature specimen by sifting the pine needle litter near the cones. Wet litter and waning daylight eroded my immediate interest in doing so, however. Today, after a week of rain-free, litter-drying weather, and with the sun high in the sky, I returned to complete the task. And to great success!

One of three female O. praticola sifted
from pine needle litter.
An electrical box made a
convenient sifting table.
I sifted one sweep net full of black pine (Pinus nigra) litter and collected 18 spiders and 3 identifiable species: the linyphiids Tachygyna vancouverana and Tenuiphantes tenuis, and my quarry, Ozyptila praticola. This time, there were three females among the O. praticola in addition to several juvenilesFinally, I can verify the presence of the species in Kent!

Covington sampling site
Kent sampling site
I had time for one more sample before sunset (sunset at 4:30 pm really limits field work!), so proceeded east into Covington. Another row of black pines separating two parking lots was my cone source. Some cones had fully opened scales, others only partially, and they were lying on bare soil or a very thin layer of pine needles and maple leaves. I tapped 72 cones and collected only 5 spiders and 2 species: T. vancouverana and an Erigone to be identified to species later.