Thursday, September 22, 2016

20-Sept-2016 Marysville, Arlington and Mt. Vernon, Washington

Site location map. Click to enlarge.
Time to re-draw the Ozyptila praticola (Thomisidae) range map again!  I returned to the field this week to continue my search for the northern edge of this introduced crab spider's range in western Washington.  I had previously sampled the urban corridor along Interstate 5 as far north as Arlington (as well as several non-urban sites well beyond there), but had not found any O. praticola beyond Granite Falls.

Although I sampled in Arlington in October 2015, I considered the city under-sampled since I had only tapped one full set (50 cones) and one partial set (13 cones) of cones there.  Further, the partial set of cones had been lying in tall grass, a situation that I've found to be unattractive to O. praticola in western Washington.  So I returned to Arlington in search of at least one more set of more suitably situated cones to tap.

Arlington Denny's

A welcome sight right off
the freeway
Fallen cones on pine needle litter: a
good place to look for O. praticola
Exiting I-5 onto eastbound Route 530, the first thing I saw was a Denny's restaurant with black pines (Pinus nigra) growing next to its parking lot.  How fortuitous!  Most of the 50 fallen cones I tapped had only partially opened scales and contained significant amounts of organic debris, but also 32 spiders from 6 families.  Forty percent of them (13) were juvenile Crustulina, presumably sticta (Theridiidae), a spider I have found in fallen cones before, but rarely.  Interestingly, all 13 were from a small number of neighboring cones.  The next most common spider present were juvenile Enoplognatha ?ovata (Theridiidae), a common spider in urban cones in western Washington.  As for O. praticola, it was a no-show until I tapped my 49th cone, which produced a mature female!

Mt. Vernon

An inviting spot south of Mt. Vernon
Lots of cones but few spiders
Next stop was Mt. Vernon, a lovely little city in the Skagit delta.  I searched downtown and the industrial zone to its south for pines, and found many.  But what I didn't find were cones.  Groundskeepers had swept them all away.  It wasn't until I hit the city's southern rural outskirts that I found an accumulation of accessible pine cones.  Black pine once again, this time planted along the fence at a plant nursery.  I tapped the usual 50 cones but only got 4 spiders: all juvenile Philodromus (Philodromidae). Oh well.

Marysville Public Works

How could I resist?!
Excellent fallen cone microhabitat
at Marysville Public Works
Heading home towards Seattle, I decided to take the scenic route from Mt. Vernon through Marysville before returning to the hurly-burly of the interstate.  I'm sure glad I did!  Just a few blocks before I had to get back on I-5, I spotted a delicious row of large black pines growing along the fence line of the Public Works.  Only one tree was accessible to me, but it had dropped plenty of cones that a) had escaped groundskeepers and b) had accumulated on pine needle litter.  I was in clover.

Male Crustulina sticta. Note the
Steatoda patterning on his dorsum.
The characteristic granulations were
visible on the sternum as well as carapace
So much so that I didn't pay attention to the time (6:30 p.m.) and almost got locked into that parking lot!  I had just captured the spiders from cones 41 through 45 in my dry vial when I heard the gate being dragged closed.  That sure snapped me out of my reverie!  The employee kindly held the gate for me while I jumped in my car and zipped by, one thumb still stoppering my dry vial.  As soon as I cleared the gate I had to pull over and transfer those spiders to my alcohol vial.  Although I had only managed to tap 45 cones, I collected a whopping 45 spiders!  Twenty-six of them were juvenile Philodromus, 7 were Tenuiphantes tenuis and 6 were O. praticola.  I also captured 3 more Crustulina sticta, including a mature male.

At present, Arlington is the northern edge of O. praticola's known range in western Washington.  The search will continue...

Evening sun illuminates the Marysville water tower.

Rich farmlands of the Skagit delta were just across the
street from my Mt. Vernon site.

Saturday, September 17, 2016

A Preliminary Look At The Phenology of Adult Ozyptila praticola (Thomisidae) in Western Washington

Whenever I take a break from collecting, I'm itching the whole time to resume field work as soon as I can.  But breaks do give me time to take an unhurried look at the data I've recently collected to see whether I've learned anything unexpected.  I've been doing this with my Ozyptila praticola project data.

The goal of the O. praticola project has been simply to determine the distribution of this introduced crab spider in Washington state, as found in the fallen conifer cone microhabitat.  But in the process of pursuing that goal, I've collected some interesting life history data on the species.  In this case, adult phenology.

The Spiders of Europe and British Arachnological Society's Spider Recording Scheme ("SRS") web pages for O. praticola both report that mature males and females have been collected every month of the year in their regions of coverage. Similarly, within their local range here in Washington, I have found adult O. praticola present every month that I've searched (February through November) except for February, a woefully under-sampled month represented so far by only one 50-cone sample.

Before graphing the monthly occurrence of females and males in my collection, I standardized numbers of specimens of each sex I collected each month by converting them to a per 100 cones tapped basis.  I did this because sampling effort -- defined here as numbers of cones tapped per month -- varied greatly from month to month (see chart, right).

The resulting chart shows that female O. praticola have been present in my samples in fairly consistent concentrations of about 1 to 2 spiders per 100 cones every month I've sampled (excluding February, as previously discussed).  In contrast, I found males in tapped cones only in spring (April & May) and fall (September & October), and at varying concentrations.

Adapted from British Arachnological Society's
Spider Recording Scheme
Although SRS reported O. praticola males present every month, it also showed a bimodal distribution with more males having been collected in May & June and, to a lesser degree, in September, than any other month (see chart, right).  Unfortunately, it is not possible to know whether this apparent similarity in patterns between my data and data reported by SRS is meaningful since it seems doubtful that the SRS data were standardized for sampling effort, as mine were.  The SRS results could be explained simply by more British spider collectors being active in spring and fall than other seasons.

Note that my phenology chart is based on preliminary data from a study not yet completed.  So far, I've tapped 268 O. praticola from 1,895 conifer cones.  Of those 268 O. praticola, 29 (11%) were female, 14 (5%) were male and 225 (84%) were juvenile.  That's not a lot of specimens to base any conclusions on.  Still, it's more data than we had a year ago, which was almost nil.  I am excited to know whether the patterns in my chart will change with the addition of more data.  And so, as usual, I am itching more than ever to get back out into the field.