Wednesday, August 15, 2018

Brown Widow

Alee Huerta of our Master Naturalist chapter sent me this picture of a Brown Widow spider.  Although somewhat blurry when she photographed through a clear plastic box (a very reasonable precaution), it is still quite identifiable. She said that "It was super fast compared to how a Black Widow moves. Its web was very dense and it had multiple ant carcasses in there that it had been feasting on."

Brown Widows or Latrodectus geometricus are not a famous as their notorious cousin, L. mactans.  They are smaller and lighter in color, ranging from tan or gray to brown.  Their famous hourglass is yellow to orange rather than bright red.  They also have distinctive stripes on their legs as seen above.
Brown Widow dorsal view - Bill & Mark Bell CC

Brown Widow egg sac - Wikipedia

Some evidence suggests that they are more aggressive than their black cousins and are displacing them in California.  This may be good news for us as they are have a less toxic venom and their bites less serious.  Either way, Widow spider bites are unpleasant and painful although rarely lethal.

 Click to enlarge -INaturalist

The map from INaturalist suggests that although they are uncommon outside of the southern states, some are occasionally found further north.  This is likely caused by their accidental transport by us bipeds that now are the most invasive species.  We are the only species to have ever covered all of the continents on the globe.* 

World wide distribution - Donald W. Hall,
Although the brown widow's range is reported to be in California and the deep south, Alee's sighting and others shows that they are now tolerating the temperatures of the Midwest, suggesting that global warming is having an effect on where they Brown Widows in this link.
* Yes, we are the only species that has covered the entire globe in its 4.5 billion year history.  That "fun fact" and many others come from Darwin Comes to Town, a book that I would highly recommend.  It focuses on the fact that evolution is occurring much faster than we ever dreamed.