As mentioned, spikes are a maggot and they can be found in several colors. How they get the color into them I haven't a clue, but red, yellow, blue and their natural buff colors are the common ones.
Waxies are very easy to keep while spikes are a challenge. My preferred bug for winter crappie fishing is a spike, a red one, but being hard to keep this is how I deal with them. They'll pupate [turn into little black, hard cylinders] in a heartbeat if they get too warm. I get mine by the 1000.
Once purchased at a bait store they go home and into the coldest portion of the bait refer that isn't down to freezing temps. They go into a large bait puck at the bait shop to help insulate them. When I want to use some, I use a smaller bait puck to hold three or four dozen, enough for the day of fishing and those left over get discarded at the end of the day.
Spikes and the goldenrod grubs are different creatures but both are my preferred winter baits. Sunfish generally get the goldenrod grubs, crappies spikes. I prefer the red spikes over any other color, the goldenrod grubs stay natural. Goldenrod grubs, incidently, are easy to gather and keep in a cold garage. I take them out of the galls the night before and carry a couple dozen in a film canister and some sawdust. the goldenrod grubs are from the green gall fly and are also a "clean" maggot like the waxie. Goldenrod grubs are about the size of a BB. Of all of the winter baits available in the north, those spikes are by far the toughest to keep even if they are the best thing to use.
Spikes are a seasonal bait due to the fact that they are so hard to keep in warmer conditions and I seldom see them available until after mid-October. One source that may have them earlier ifs Vados Baits. Do a google search and you'll find them in Minneapolis, Minnesota and they do ship.