Dead Age

Scavengers (not to be confused with Undead Scavengers, that's a completely different category of enemy) can only be found as a negative consequence of a failed encounter. As such, they will never show up as a regular "Area" enemy, like most Undead, nor will they attack your camp, like Undead or Punks.

Scavengers are the most common of miscellaneous enemy, as they can show up in any zone. Being ambushed by Scavengers are often the consequence of failing certain encounters, especially ones for looting vehicles (Trucks, Buses, etc.), looting aerial drop zones, or ransacking other places you'd expect humans to be looting during an apocalypse. As scavengers tend to attack in groups of two or three, you will only need to encounter them a maximum of five times to unlock both related scavenger achievements, and since you'll fail a lot of encounters early in game, meeting your quota of ten scavenger kills shouldn't be a problem.

Given their common-ness, keep in mind that fighting humans (including scavengers) is a much tougher battle than fighting undead, as humans carry firearms and thus do much more damage than your run-of-the-mill undead.

Only enemies labeled as "Scavenger Assassin", "Scavenger Brawler", "Scavenger Charger" or "Scavenger Marksman" count for this achievement.

Scavenger Assassin Stats
Fast: No
Immune to K.O./Stun: No
High Defense (aka needs Breakthrough): Yes
Special Abilities: Headshot (Stun), Exploding Trap (Trap)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 5
Locations: Failed encounters

Scavenger Brawler Stats
Fast: No
Immune to K.O./Stun: Yes
High Defense (aka needs Breakthrough): Yes
Special Abilities: Ticking Bomb (Delayed AoE)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 4
Locations: Failed encounters

Scavenger Charger Stats
Fast: No
Immune to K.O./Stun: No
High Defense (aka needs Breakthrough): Yes
Special Abilities: Wary Eye (Counters Ranged Attacks), Shrapnel Spray (AoE)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 7
Locations: Failed encounters

Scavenger Marksman Stats
Fast: No
Immune to K.O./Stun: No
High Defense (aka needs Breakthrough): Yes
Special Abilities: Return Fire (Counters Ranged Attacks)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 8
Locations: Failed encounters