Snakey...I had some in the fridge for a week once and they were fine...can't tell ya how long they would have lasted after that, cos i 'Drowned Them'. Turning them into casters is simple...keep them in a dry warm place, and it shouldn't take too many days for them to turn.
Go get em!
u better watch it though m8, u know what maggots are like for escaping  and if their in a fridge with food in ur gonna be in for a disaster waiting to happen[!]. Mags can last for ages in fridge. After the maggots start turning to turn to caster put them in vinegar in a bag with no air in. Hope this helps m8 see ya
Turning your own casters is a time consuming effort.You need to riddle them off every four hours or so. this is so no bad casters go through.You will probably need 4 pints of white maggots to get 2 pints of casters.Probably easier buying them in but do not get the prepacked version they stink when a hook goes in.get the tackle to riddle them off while you wait if you can as they will be the freshist available.
I once was sold some 'preserved castors' that used a vey weak solution of formaldehyde in the bag and was told that they would make no difference, just to rinse them first - managed not to catch a thing using them 
during the summer i turn up to a gallon of casters a week for me sammy & phil.
the best way is for 3 pints of mggots riddle them off to cleanthem then put them in about 3 pints of damp sawdust this stops them shrinking keep the container in a dark cool place & riddle the casters off once or twice a daythen you can keep them for up to 2wks in clean water but change the water every 2 days.
if you want to keep maggots in a fridge or anywhere dry & cool
leave the lid off that way they wont sweat & climb out.
Not sure bout how long but i kept some for two weeks once and they were fine so... For caster's. when the maggots start changing siv them regularly and any caster keep in an air tight bag in cold water this always works for me!