Veins on floor joists?

I recently was under a house in southeast Missouri and found something I have yet to encounter in 5 years of inspecting. Any help on what this might be is appreciated. It looks like roots but it starts and ends on the individual joists.

Fungus , did you take a moisture reading?

I agree with Wayne, That is what it looks like.

Looks like varicose veins.

Agree with Wayne
Commonly called bootlaces
http://en.wikipedia.org/wiki/Mycelial_cord

Adam,

Most likely dry rot fungus, which in severe cases like yours is expensive to repair.