Help with ID, please?

[wec2024]

This spider fell out of my pant leg after I had left pants on the floor overnight. I'm in NW Illinois and hoping someone can help me identify what kind it is. It's a bit less than 1" including legs; distinct red stripe on back side of abdomen, and slightly less distinct reddish marks on anterior underside of abdomen. First photo looks brownish but it's really quite black looking. Sorry for poor image quality, but I could only photo through the jar it's in. It's pretty quick in how it moves - not jumping, but just fast. I can't find anything like it in the guides, pretty sure it's not a black widow...? I'm a retiring wildlife biologist who normally works with mammals, but I'm curious about All the Things. Thanks for any help!

 

[Tbone192]

Looks like Castianeira crocata, likely an adult female. Nice find!

 

[wec2024]

Thanks! Just looked it up and it looks exactly right. Are they uncommon?

 

[fcat]

That's a cute spider, had no idea it existed

 

[aaarg]

Thanks! Just looked it up and it looks exactly right. Are they uncommon?

they've got a wide range (eastern north america) and are fairly common. there are a couple species that look similar, namely the more-common Castianeira descripta. C. longipalpus is by far the species i see most often, but it has white stripes rather than a red spot.

fast & active ground-hunters!

 

[wec2024]

Excellent, thanks! When I took it (her?) outside to release, she ran off super fast. Fast and active makes sense based on how she moved in the jar and when I let her go.

 

[Tbone192]

If I'm not mistaken, most of the genus consists of ant parasites. They mimic ants and their signals, which allows them to feed freely upon the colony safely. Certainly a daring feat for a spider.