Last week was my birthday, and as is my usual custom I took the day off in favor of the season’s first “official” bug collecting trip. Falling in late April as it does, my birthday usually coincides nicely with insect activity beginning in earnest here in Missouri, and for this year’s edition I decided to look for Cicindela scutellaris lecontei (Leconte’s Tiger Beetle) on sand prairies in the extreme northeastern corner of the state. Sadly, this year’s unusually protracted spring had resulted in a mostly still-sleeping landscape, and whatever hopes I had of seeing the earliest emerging adults were dashed as thick, gray clouds hung stubbornly in the sky and temperatures refused to edge much above 60°F. Still, a bad day of collecting is better than a good day of just about anything else, and in such situations there are still wintertime collecting methods—peeling bark, cutting wood, breaking stems, etc.—at my disposal.
While exploring a sand prairie at Frost Island Conservation Area (Clark Co.), I found a large, dead willow in one of the draws that had apparently been killed by recent prescribed burning activities, and when I peeled back a section of the trunk bark I found this medium-sized spider (leg spread ~40 mm) sitting underneath. Based on general appearance I first thought it was some type of wolf spider, although it struck me odd that it would be under the bark of a tree rather than on the ground where wolf spiders are normally encountered. However, after consulting BugGuide and not finding it among the wolfies, I decided to widen the net and quickly stumbled onto the fishing spiders (genus Dolomedes, family Pisauridae). I’ve seen fishing spiders before—normally they are found at water’s edge and periodically demonstrate a remarkable ability to dash across the surface of the water to grab an errant insect, using the same surface tension for support that had trapped its hapless prey. As odd as it would have been to find a wolf spider high up in a tree, it seemed even more unlikely that I would find a fishing spider in such a dry, arboreal habitat. Things became clearer, however, after I settled on the species D. tenebrosus (dark fishing spider)—distinguished from other fishing spiders by the interrupted white borders behind the “W”-shaped markings on the abdomen (see BugGuide). According to Jacobs (2002) this species is frequently found far away from water, usually in wooded settings, and hibernates as an immature adult (penultimate instar) under—you guessed it—loose bark (also stones). Barnes (2003) also provides a good discussion of this spider along with diagnostic photos and references for further reading.
Based on this information, I’m guessing this individual is a still hibernating subadult, presumably a female based on the small pedipalps (the little “legs” next to the mouth). The spider moved slowly across the exposed wood as I took these photographs, wandering onto sections of different color as she did. I like the two photos for different reasons—the first (light background) seems to better show the shape and silhouette of the spider, while the second (dark background) highlights the spider’s beautifully intricate markings.
Barnes, J. K. 2003. Dark fishing spider. University of Arkansas Arthropod Museum Notes 15 [full text].
Jacobs, S. 2002. Fishing spider, Dolomedes tenebrosus. PennState College of Agricultural Sciences Insect Fact Sheet [full text].
Copyright © Ted C. MacRae 2014