A study of Tigrosa

I don’t usually talk about much beyond birds, plants, and a selection of hexapods.  However, my interests, and even my job, lead me to the study of all manner of organisms (mainly in the kingdoms PlantaeFungi, and Animalia).  Although I won’t post much about these less popular groups, I do seek them out at times.  Sometimes I study them out of the blue but other times my interest in them is provoked by an encounter.

Arachnida is a class that I generally avoided because I realized that there are tons of different species and that some of them are awfully difficult to ID without a specimen.  I can’t justify killing a specimen just to satisfy a casual interest and, although I’m not an arachnophobe, I don’t try to handle a lot of live specimens.  Smaller spiders, such as Jumping Spiders (Salticidae), aren’t terribly aggressive and can be put in a clear Zip-loc bag to examine under a dissecting microscope.  Unfortunately, these are often quite fast and hard to focus on.  I am actively utilizing this technique but I usually just scavenge dead specimens.  Somewhat to my chagrin, our park has a contract with an exterminating service that sprays some of our buildings.  This does prevent harmful species, such as the Southern Black Widow (Lactrodectus mactans), fromo coming into close contact with the unsuspecting public.  However, many harmless species are killed as well.  Their deaths are not in vain, for I collect them and study them.

Once I have an ID I add them to the Arkansas State Park’s Natural Resource Inventory Database (NRID).  This is a neat program that other states’ park systems have implemented and one that we are in the infancy stage of curating.  Our database is, or will soon be, available to the public.  Visitors can see and eventually add records to the park’s list that they are visiting.  Identifying wildlife to further my knowledge of local ecosystems is one of my job duties as a park interpreter which is great because that is one of my top interests.  Of course, my main focus is birds, butterflies, dragonflies, herps, and plants.  However, I have since been exposed to many other taxonomic groups and have loved every minute of it.

My most recent find is a wolf spider (Lycosidae) that was in the throes of death just outside the bathhouse of Logoly State Park (Columbia County).  I was quite familiar with this spider as I had studied it earlier in the year after photographing a live specimen fleeing from my presence along our Spring Branch Trail.  I guessed it to be Tigrosa georgicola but felt that I didn’t have enough for a proper ID.

Tigrosa georgicola

Tigrosa georgicola

Several years ago I was mowing and I flushed a large wolf spider up the side of our house.  I identified it as Hogna aspersa (no common name).  Surprisingly this ID was correct as I have since confirmed (confirmed may be too strong of a word) it after becoming more interested in Araneans.  So, I began my study of the live individual at the genus level: Hogna.  To my surprise, this genus is currently being either dismantled or restructured.  Many that were in Hogna are now in Tigrosa.

My first, and probably last, attempt at drawing Lycosid eye arrangement

My first, and probably last, attempt at drawing Lycosid eye arrangement

I brought my dying spider in to my desk and set it under my dissecting microscope, using my laptop screen for lighting (which was actually quite adequate).  My first guess was T. georgicola for that was what I believed my previous, fleeing specimen was.  The main feature that made me think the original specimen was georgicola was the fact that the dorsal stripe was pronounced and continued throughout the thorax: from face to abdomen.  I had read, via bugguide.net, that the ventral coloration of the abdomen was quite distinct and separated it from similar species, such as T. helluo.  Now, I had an actual specimen to flip over and examine the ventral side.  Hurray!  Unfortunately, this came at the expense of this specimen’s life; although, it had probably run the course of its life as most wolf spiders I have seen this year have already mated and birthed young.  When I turned it over I found a nice, contrasting landscape of Halloween’s orange and black.  There were two orange stripes in the median of the venter and the flanks of the venter were mottled black-orange.  The zebra dilemma arises: black with white stripes or white with black stripes.  Most georgicolans are orange with three black stripes running down to converge at the spinneret.  This individual had two orange stripes that fade before the apex of the abdomen, where the spinneret is located.  These two characteristics are apparently unique to this species.

Tigrosa georgicola dorsal.  Note the extent of the thoracic stripe

Tigrosa georgicola dorsal. Note the extent of the thoracic stripe

Tigrosa georgicola face.  Dorsal stripe extends to mandibular area.

Tigrosa georgicola face. Dorsal stripe extends to mandibular area.

Tigrosa georgicola ventral.  Note the black and alternating orange coloration.

Tigrosa georgicola ventral. Note the black and alternating orange coloration.

This process describes a portion of my workload as a park interpreter at one of Arkansas’ natural parks.  This is definitely one of my favorites aspects of the job.

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