Pardosa lapidicina U.S. tour

Identification of species has two faces. It is as important to know what the organism is as what it isn't. Both are required to confidently identify it because we know that some species are easily mistaken for others. Species identification in the Pardosa genus in general and the lapidicina group in particular has long relied on microscopic examination of genitalia rather than general appearance, colors, and patterns. Almost no attention is been given to macroscopic features and it's rare to find a scientific paper with an image of a live spider let alone an array of photos at different stages of development which would be necessary for making reliable macroscopic identifications in the field or in front of the computer.

Using the process of elimination only works if we know what all our options are, and for that we often look at range maps. Looking at the various published maps for the lapidicina group shows a single species, P. lapidicina, standing alone in the eastern half of the county. Since the lapidicina group is relatively easy to recognize from general photographs, it makes for an easy species identification there despite a variety of forms ranging from very pale to brown or black. No lapidicina group species are shown for about half of the eastern states, but looking at observations at iNaturalist shows them in many of those. Clearly, their range hasn't been fully explored. This didn't surprise me since my search for lapidicina group spiders in central Texas showed them numerous in widely scattered locations and rather particular about their habitat. In fact, I had to work pretty hard to find them at all. I eventually decided they were all Pardosa mercurialis.

As I started trying to establish what my local species options were, I noticed there were no lapidicina group observations at iNaturalist from a large block of counties in eastern Texas. It was impossible to know if they were there but had been overlooked so far. I looked in Louisiana and found nothing. I looked in Mississippi and found nothing. At least P. lapidicina was supposed to be there according to the literature. I looked in Alabama and finally found some lapidicina group individuals. P. lapdicina is the only option. The principal form is an attention getter with patches of black and near white in a messy checkerboard pattern. I was able to find similar spiders in other southeastern and mid-atlantic states. By the time I got to New England, the principal forms were drabber and darker. All could reasonably be identified as P. lapidicina since it was the only known option. About this time I noticed my local mercurialis were yellow on top of the trochanter, a short, mostly bare segment at the top of the leg which is often visible in images at iNaturalist. I also noticed that lapdicina was black in the same place. Finally a clue that might help to tell the species apart!

I continued to search westward to the limits of the published range for lapidicina along the eastern slopes of the Rocky Mountains and down to Oklahoma which was supposed to only have mercurialis. Observations at iNaturalist suggest that was generally true. I found some apparent mercurialis farther north comingled with apparent lapidicina. I ran into a problem with the lapidicina group spiders along both sides of the Mississippi River where the principal form was dark brown with muted markings. Spiders which were fairly similar came with either yellow and black trochanters making this clue appear unreliable in the region. Of course, this needs further investigation

Although I originally had lapidicina as one of my local options, my virtual lapidicina tour helped me conclude they weren't in Texas after all and strengthened my species identification of mercurialis.

Posted on Αύγουστος 15, 2021 1132 ΠΜ by eaneubauer