Saturday, March 30, 2013

A Kansas Welcoming Committee...

I bet you were just sitting around wondering, "How the hell do you tell the difference between a Southern Black Widow (Latrodectus mactans) a Western Black Widow (Latrodectus hesperus) and a Northern Black Widow (Latrodectus variolus)?"  Well, it has nothing to do with how they talk, that's for sure.  And what perfect timing you have; I was just sitting down to blog about this very subject.  

You see, while scavenging through a pile of cement rubble for border material for one of my new raised beds, I came across my first Kansas widow.  Immediately I exclaimed, "Awesome!  My first Western Black Widow!" (okay, maybe I didn't, but I thought it).   Moments later, however, that creeping little voice in my head reminded me that I have never actually bothered to learn the distinguishing characteristics between the three black widows possible in the U.S. and I that I didn't even have a clue about their range overlap.  BugGuide quickly helped me with this dilemma.  So, here is a quick summary of what I learned that will help me (and maybe you!) feel more confident in future black widow identifications. 

1. Referring to some BugGuide info and a few other internets resources, there is some degree of range overlap for the three species of widow. Though it seems like the Northern and Southern widows try to stay mostly Eastern. 
Range map for Western Black Widow
Confirmed occurrences (dark brown) of the Western Black Widow, courtesy of BugGuide
Range map for Southern Black Widow
Confirmed occurrences of the Southern Black Widow, courtesy of BugGuide

Range map for Northern Black Widow
Confirmed occurrences of the Northern Black Widow, courtesy of BugGuide


2. Dorsal markings are not as important for identification as I initially thought.  Southern widows tend to be all black overall (aside from the hourglass) at maturity.  Mature Western widows also gain an overall black or even "shiny brown" appearance.  Northern widows can apparently have a row of red spots and white bands dorsally even when mature.   However, all immature widows can show a huge variation in the presence and degree of dorsal red and white markings when immature.  Take these images for example:

I photographed this sizable specimen on top of Stegall Mountain in Missouri.   I am going to assume this is  a mature Northern widow, remember the thing about Northerns retaining dorsal red spots?
Stegall Mountain, Peck Ranch Conservation Area, Missouri
 This slightly smaller specimen found under some rocks displayed some really great dorsal markings.  I am going to assume again a Northern widow since I did not photograph its hourglass.
Rock Bridge Memorial State Park, Columbia, Missouri
Now here is the specimen in question.  The Black Widow that inspired me to learn!  I'm going to call this one a Western widow.  You will see why in a second.
Immature Western Black Widow, Holcomb, Kansas
 3.  The HOURGLASS is very important!  Though one source sites exceptions to these general rules, the following hourglass specs can be useful in ID'ing widows.  Northern widows tend to have an hourglass marking that is not connected in the middle.  Western and Southern widows have connected hourglasses, however, in the Western widow, the two halves of the hourglass will be similar in size and shape.  The Southern widow will have an hourglass with the half closest to the abdomen tip almost rectangular in shape.  
Western Black Widow (specimen in question) hourglass, best I could get inside a clear container.


Black Widow - Latrodectus mactans - female
Southern Black Widow hourglass, Chris Wirth, BugGuide

Black Widow - Latrodectus variolus - female
Northern Black Widow hourglass, Chris Wirth, BugGuide
So, anyways, today I did meet my very first Western Black Widow (we'll see what the experts on BugGuide say....)!  I need more rubble for my garden...




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