Latrodectus mactans vs Latrodectus hesperus

[Tarantula155]

Is there any key differences between the two species? That is visible, not just they're native range.

Are they both equally toxic?

I noticed the widows here in Colorado (hesperus) are more aggressive and tend to have much thicker webbing compared to the widows I had in Virginia (mactans)

 

[The Snark]

A place to start. https://sites.google.com/site/widowman10/ PM him here or hope he weighs in on this thread.

 

[Chris LXXIX]

Without having a clue about hesperus, i vote mactans, because that Latin word is awesome and that spider is very cool IMO
And tredecimguttatus as well, since here in Italy she managed to kill five people decades ago in Five Lands deserve respect (don't know, but i doubt, if in those days here the antivenom for Latrodectus sp. available in USA was available here in Italy Hospitals)

 

[Tarantula155]

A place to start. https://sites.google.com/site/widowman10/ PM him here or hope he weighs in on this thread.

This was quite helpful indeed.

 

[Tarantula155]

So I took a pic of my particular widow today after her meal, (I am located in Colorado) not sure if my widow is a Latrodectus hesperus because it has a tiny red dot at the end of it's abdomen.. correct me if I'm wrong but isn't it only mactans that have it?

 

[The Snark]

Or another possibility. Carefully compare the hourglass to that of a Geo. Yours appears the lower triangle section is broader. http://cisr.ucr.edu/identifying_brown_widow_spiders.html & https://sites.google.com/site/widowman10/different-color-morphs-of-geo

 

[BobGrill]

Admittedly, widows have always sort of creeped me out, but the hour glass on yours is very pretty.

Sent from my LG-D801 using Tapatalk

 

[Widowman10]

Judging by this picture alone, your spider appears to be a geometricus. Did you by chance catch this spider in the Denver area?

I say this for several reasons:
- while it is true that mactans typically has the red dot dorsally near the spinnerets, I do not believe this is mactans, it is way too far out of range (among other reasons)
- the glass appears more orange-ish in color, rather than red
- the glass shape (nice triangle on top, broad larger triangle on bottom) is typical of geo
- 4 yellow dots surrounding the spinnerets are normal in geo (I have seen these on some very juvenile hesperus as well, but the browns show them much more often)

None of these alone should determine species of course (and it is ALWAYS easier to ID in hand or with more pics), but all together they can make a decent case for geometricus. I have seen some almost completely black geometricus (thanks for the link to it, Snark) in my time, and they have a weird 'sheen' to them. So even under light and a close eye, they have a different look or texture to them than the native blacks. Kind of hard to describe unless you see it (maybe almost shiny velvet?).

Hope this helps, please let me know the location when you get a chance. If you found this in the Denver area, I'd be that much more sure of it being a geometricus.

 

[Tarantula155]

I'll try snatching a few more pics, here is a before feeding pic (notice she's much thinner) I also used flash in the pic where you mentioned it looks orangish, so that probably what made it seem like it.



Here is a pic of here when I first captured her!


This specimen was caught out in Parker, on Jordan road near the Bronco's practice center!

 

[Widowman10]

Interesting. Wish I could see the spider in hand to know for sure!

 

[Smokehound714]

If found in dry desert habitat, it's likely hesperus, IMO.

hesperus LOVE the desert, sagescrub, and chaparral.

 

[The Snark]

So it's a Geohesperus-Mactans. Simple. ::

Look very closely at it's upper arms. If you see Proudly Made in the USA it's from the Detroit area and a Variolus, if you see a heart with an arrow through it and MOM, it's a southerner Mactans, if you discern Born To Raise Hell it's a Geo and if you see the No Fear or Nike insignia it's a west coast Hesperus.

 

[Widowman10]

Huh, missed the added pictures until just now, that's definitely a hesperus :clap:

Thanks for posting more pics, that helped.

edit: Looks like I cannot go back and edit my original post to add anything. What I wanted to say was that this is good evidence that 1 picture alone is never sufficient for a positive ID. Characteristics can be skewed into looking differently than they really are- and this is a perfect example! It is always better to have more pictures, and ideally, the specimen in hand to observe. Thank you for posting the other photos, they helped tremendously! This thread is a great lesson for 1-picture visual IDs. :clap:

 

[The Snark]

Huh, missed the added pictures until just now, that's definitely a hesperus :clap:

Thanks for posting more pics, that helped.

edit: Looks like I cannot go back and edit my original post to add anything. What I wanted to say was that this is good evidence that 1 picture alone is never sufficient for a positive ID. Characteristics can be skewed into looking differently than they really are- and this is a perfect example! It is always better to have more pictures, and ideally, the specimen in hand to observe. Thank you for posting the other photos, they helped tremendously! This thread is a great lesson for 1-picture visual IDs. :clap:

Widowman, I realize I'm abusing your generosity here but I again reiterate the need for ID criteria that you use. I'm guessing abdominal shape and proportional differences of leg segments. This would also serve to demonstrate that rule of thumb coloration, and variations in the coloration, IE Hesperus are always entirely black (unless they aren't) isn't proof positive.,

 

[Widowman10]

Widowman, I realize I'm abusing your generosity here

No, not at all! I should have specified when I replied anyway.

The dorsal shot sealed it. The abdominal shape helps, but you can see the 'herring bone' white marking near where the abdomen meets the cephalothorax, which is so very distinctive in hesperus. Hesperus also retain 'squashed circular' white markings as the juvenile coloring fades, also very distinctive! Here is an example of what I'm talking about (pulled a random image from bugguide):
http://bugguide.net/node/view/841349/bgimage

 

[The Snark]

No, not at all! I should have specified when I replied anyway.

The dorsal shot sealed it. The abdominal shape helps, but you can see the 'herring bone' white marking near where the abdomen meets the cephalothorax, which is so very distinctive in hesperus. Hesperus also retain 'squashed circular' white markings as the juvenile coloring fades, also very distinctive! Here is an example of what I'm talking about (pulled a random image from bugguide):
http://bugguide.net/node/view/841349/bgimage

Shazam! Easy to spot it when you know what to look for!

I had the exact same facepalm obvious yesterday. Two people discussing who made the 150 foot cell phone tower next to the restaurant. Just a glance was enough and I told them it was a German design. How could I tell that? Like that white mark on her abdomen. Oh, that lower truss has a truss. Anti vibration. Fussy Germans always go the extra little bits.

 

[Tarantula155]

My widow molted recently! I'll throw a pic later, she's jet-black now

 

[Tarantula155]

Jet-black now!