You certainly can. You can either put a female wailmer and a male wailmer in the daycare, or place a ditto in the daycare with any gender wailmer.
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If you breed a female Skitty and a male Wailord then you get a Skitty but if you breed a female Wailord and a male Skitty then you'll get a Wailmer.
I don't even think you can breed those two pokemon. But if you try it, and something happens, let me know. :p
Wailmer pail waters the plantes
a water stone evolves wailmer
Wailmer evolves at Level 40.