They're just hiding..... waiting for an unsuspecting miner to wander just a biiiiiit too close, and then snatch you up and go all NOM NOM NOM on you....
I just completed both the Deep Dives and YES YOU ARE ABSOLUTELY RIGHT! I don't think I see a single leech! Also, I think this week is pretty easy even for elite. My friend and I finished it with 2 greenbeard easily.