"…digging for a living can be pretty hard work at times. The kinds of earthworks that moles produce depend very much on the nature of the surroundings in which they find themselves; however the way they dig them depends on their evolutionary history" [Gorman & Stone, The Natural History of Moles]
“But the revolution is thoroughgoing. It is still travelling through purgatory. It does its work methodically [...] And when it has accomplished this second half of its preliminary work, Europe will leap from its seat and exult: Well grubbed, old mole!†[Marx, The Eighteenth Brumaire].
Marx’s mole is the revolution, which surfaces in times of open class conflict and then retreats underground to burrow its tunnels; moving along with the times the mole re-surfaces unexpectedly.
The word pioneer means “a soldier responsible for excavations and tunnelling; one of a body of foot-soldiers who march with or in advance of an army or regiment, having spaces, pickaxes etc. to dig trenches, repair roads, and perform other labours in clearing and preparing the way for the main body’; also, by extension, a miner". By the 1830s, the metaphorical sense of a pioneer as explorer or initiator had taken on a specific reference.
“There are also enemies in the bowels of the earth. I have never seen them, but legend tells of them and I firmly believe in them... it is of no avail to console yourself with the thought that you are in your own house; far rather are you in theirs†[Kafka, The Burrow]