The excavator spider

Garden Apr 3 2016-2964 cropped

Guest post by Staffan Lindgren (@bslindgren)

The other day I was practicing macro photography (I am still learning after several years of erratic success at best, so please excuse the imperfections) trying to patiently wait out some Halictus sweat bees with my camera. The bees appeared to be much more patient than I was, however, by which I mean that they sat deep in their burrows, apparently staring me down. So I wandered around looking for other potential subjects to practice on. While examining another bee burrow, I saw a slight movement in the dirt in a spot about 10 cm from the bee burrow. A closer look revealed a very attractive wolf spider hiding in a small depression.  In spite of its gaudy colours (for a wolf spider) it was rather well camouflaged against the dirt. As I watched it, it started to move, and to my surprise picked up dirt and moved it to the edge of its little hiding spot. It remained in the depression and continued to modify it by moving dirt as I attempted to take some photographs.  From what I could tell, it looked as if it used its pedipalps to hold the dirt against the base of its chelicerae to move it, rather than only grabbing it between the chelicerae.

Garden Apr 3 2016-2964 cropped

I had no idea what species I was dealing with, so I went to the web to see if I could figure it out. It turned out to be Arctosa perita (Latreille, 1799), which confused me at first since it is a Eurasian species.  A quick check of Bennett et al. (2014) confirmed its presence. I also found the post “The mystery of the burrow-dwelling sand dune spider” about this species on Catherine Scott’s informative blog “Spiderbytes”, as usual illustrated by a number of excellent photographs by Sean McCann.  These sources confirmed that the spider occurs on Vancouver Island, and that it is a species known to make burrows.

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These spiders have some pretty good camouflage, as well as subtle but beautiful colours. Photo by Sean McCann.

Apparently A. perita was introduced in southwestern BC at some point, and it has spread enough that it now seems fairly common, at least in the southwest corner of the province. In fact, we have numerous introduced species of insects and other arthropods in BC, particularly in urban and rural areas. For example, the most commonly seen ground beetles are generally invasives, although we tend to not think of them as such because they don’t impact us directly. They probably do impact the native fauna to some extent, however, albeit not noticeable to our selfserving views. After all, even earthworms (which are almost entirely non-native in Canada) have been labelled harmful to native fauna in forest environments, at least (Addison 2009). Whether or not A. perita has any noticeable effect on native fauna is unknown, but it is an interesting addition to our Canadian fauna.

References

Addison,  J.A. 2009.    Distribution and impacts of invasive earthworms in Canadian forest ecosystems.     Biological Invasions. 11: 59-79.

Bennett, R., D. Blades, D. Buckle, C. Copley, D. Copley, C. Dondale, and R.C. West. 2014. Checklist of the spiders of British Columbia.  (Web) http://ibis.geog.ubc.ca/biodiversity/efauna/documents/BCspiderlistMay2014FINAL.pdf

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