Helen and Henry lived in Iowa for slightly more than five years.  They described the butterfly in 1870, and moved back east, where Henry held the position of professor of Mental, Moral, and Social Science in the Massachusetts Agricultural College.  Helen died there on December 4, 1874, apparently of some chronic illiness that she may have had while she was in Iowa.
The Auburn Seminary Record, Volume II, for 1906-1907 contains some reminescences by Henry A. Nelson, D.D., class of 1846.