Wednesday, January 29, 2014

Animals 2013 - Trapdoor Spider

In 2009 I found an abandoned burrow of a Trapdoor Spider.  That light colored lump to the left is actually a silken cap that can be pulled snug down to close the burrow entrance. 

When closed, the camouflaged cap makes the burrow nearly undetectable.  The Trapdoor Spider hunts by lunging out from beneath the cap to grab passing prey and then pulling the catch into the burrow for consumption.  I have always wanted to witness this spider in action.  Having found evidence that the spider lived at Blue Jay Barrens, I was keen to find the living animal.

My first encounter with a live Trapdoor Spider occurred by accident on July 1, 2013.  I inadvertently sliced the top from a burrow while hoeing weeds in the vegetable garden.  Trapdoor Spiders cover the sides of the burrow with a thick layer of silk and this was the first thing I noticed when the burrow was uncovered.  My excitement level rose quickly when I saw the spider inside.

I used a weed stem to encourage the spider from the burrow.  It crawled right out with no display of aggression.

This is one neat looking spider.  It presents an odd appearance because it seems to have ten legs instead of eight.  In this photo the spider is facing to the left.  The two short projections are the chelicerae or jaws which terminate in fangs.  Beside those, looking much like a first set of legs, are the pedipalps which seem to play a part in the mating process.  The first real legs are found just behind the pedipalps.

The shape of the carapace covering head and thorax gives the spider a distinctly crab like appearance. 

In order to capture features that may aid in identification, I took shots of the spider from as many angles as possible.  My most useful identification guide, Spiders of North America – an Identification Manual by Ubick, often requires magnified examination of specific spider parts that are obtained by dissecting a non-living specimen.  I had no intention of sacrificing this individual, so I was hoping for the best with my photos.  Fortunately, I was able to get some positive shots of a characteristic depression in the tibia of the third leg which identified this as a member of the genus Ummidia.  The keys in the manual ended at genus with a note that it was widespread in the U.S., being represented by 50 species, only 10 of which have been described.

Like a well trained dog, the spider rolled onto its back for some shots of the ventral surface.  The fangs can be seen to the left.  The light patches on the abdomen are coverings over the lungs.  Air enters the lung chamber by way of spiracles accessed through slits at the edge of the cover.

It wasn’t safe for the spider to remain in the garden, so I chose the nearest barren with suitable soil conditions as a relocation site.  This area is very similar to that in which I found the 2009 burrow.

I fashioned a new burrow by stabbing my finger into the ground and firming the soil near the surface. 

 The spider wasted no time backing its way into its new home.

I checked back a couple of weeks later to see how things were going.  The inside of the burrow had definitely been reshaped and the outside edge had been reinforced by spider silk.  Unfortunately, there was no sign of the spider.  Hopefully, the spider found a more suitable location for a dwelling and dug its own burrow.  I’m happy to have seen the live spider, but I’m still determined to see an occupied burrow in action.

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