Use a piece of carrot or potatoe...it will last alot longer..as they do not mold like other veggies will..fruit is a no-no they rot way to fast.
You want to keep some moisture in the box, but you don't want alot...rotting fruit, even a little rotted, is bad news because it creates alot of moisture. Fruit rots over nite when left out at room temp. Carrots and potatoes won't do that.
They love lettuce, but it rots faster then fruit..so you'd have to put it in the Am and take it out in the PM.
The oatmeal will last for a while. When you notice the culture starting to smell "not so nice" it's time to change it. That will usually happen around 2 months old. But, even so it's best to change it out at 2 months anyways..so they aren't just crawling around in their own pop (especially if you have a large culture).
Also, they can and will live in oatmeal...but a better bedding for them is Wheat germ, then get some alfalfa flakes and mix in...fish flakes work too.
Their container should be ventilated too. Those plastic shoeboxes at Wal-Mart (the ones for 77 cents) are the best to keep them in.
Then cut a hole in the lid and you can hot glue a piece of that plastic canvas on the bottom side. That keeps stuff from falling in, and they can't crawl out..the sides are too slick.
****************
A suggestion on breeding them...keep the beetles separate from the worms. Sometimes the beetles will eat on the worms, which of course kills them. If you wanna get all "fancy" about it...those plastic drawer systems they sell at Wal-Mart work great. That way when you see a beetle in with the worms you can move it to a beetle box lol.
The beetles lay eggs 1 week after turning into beetles, and they live for 4 months.
****************
If you want your worms to grow slower...refrigerate them. If you want them to grow faster (to get a culture going stronger) keep them between 75-80 degrees.
But always take them out of the fridge once a week and let them warm up and feed them. They don't eat while refrigerated.