Ants: Ants do not attack your Epiphyllum plants directly; instead they feed on the secretions left by other insects. Ants have been known to carry aphids and other insects from plant to plant in order to feed. They may also try to colonize your pots which can cause increased insect population come springtime.
Solution: Treat heavy infestations with an insecticide such as Triazicide. Sprinkle around the base of your plants. For pot infestations water your plants heavily 1 time and then sprinkle after watering.
Organic control can also be obtained by sprinkling cinnamon in and around your pots. Another organic method that is affective for treating ants that are traveling from plant to plant on branches is to blend several sprigs of mint leaves with a quart of water and strain thru cheesecloth. Spray the mint solution where ever ants are present.