Wow!!! That is gorgeous!!** It's a Lycoris radiata aka spider lily and some folks call them surprise lilies.*
http://msucares.com/news/print/sgnew.../sg031003.html
The surprise lilies that I have are Lycoris squamigera, but they are a pale pink and their flower is trumpet shaped.
http://www.hort.wisc.edu/mastergarde...is/lycoris.htm
More info on surprise lilies.
http://web.extension.uiuc.edu/champa...rs/050818.html
http://www.hort.wisc.edu/mastergarde...is/lycoris.htm
Do dig them after they bloom and replant them immediately.* Mine send up wide strap-like leaves in spring which disappear after about 2 or 3 weeks.* The bulbs are large and probably 10" deep.* They cost about $3.00 each, so get all you can.* They tend to like part sun, at least that's how I've seen them grown.* I've even seen them in shade gardens.* They do multiply over time.* What a gem you have found.
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.