From The Collaborative International Dictionary of English v.0.48 :
Gleaner \Glean"er\, n.
1. One who gathers after reapers.
[1913 Webster]
2. One who gathers slowly with labor. --Locke.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
gleaner
n 1: someone who picks up grain left in the field by the
harvesters
2: someone who gathers something in small pieces (e.g.
information) slowly and carefully