Answer: From what I can find, arum lily and calla lily are the same species (Zantedeschia aethiopica). It seems like the plant is referred to as arum lily when it is considered a weed, and calla when used as an ornamental. It's possible the ornamental varieties are more well behaved. (And you don't need to worry about this tender bulb taking over your Massachusetts garden.)
Here are some sites that discuss the plant, including some sources. I hope this helps.
Interestingly, these plants are considered a noxious weed in Australia:
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