Can a red virus eat a normal virus in agar.io?

The game is programmed so that all viruses spawning have a certain distance to other existing ones, but to answer your question: They just overlap, it won't be "eaten" or something.

Yes, if you propel a default virus into a spawner virus, the latter will consume it and dispense it as regular food, just as it would with ejected mass, or a player cell. (See item #5, under 'Trivia', in the agario wiki)

However, this is not always a viable option for gaining mass, as all the mass you eject to propel the virus into the spawner may amount to more mass than you ejected, and there is also a chance of other players collecting the food dispensed once you complete.

I actually did this a lot on here, when I saw a default virus that had spawned a short distance from a spawner. Another tip for 'Experimental' game mode: If you see someone small partly under a spawner virus, and no one else is around, feed the spawner very fast, and it will consume the smaller player and eject the mass. I went to 14,281 mass in <10 minutes, playing as "ᥨ᧙ᨆⅇᢺ ㊴ ßǾȿŜ" (Level 39 Boss).