Hammerlock is curious as to why the Crystalisks are so aggressive and the way they are, so he sends you off to the Caustic Caverns to find some evidence. You will notice that there are three optional objectives in this mission, all of which will require you to kill some enemies inside of Caustic Caverns. You will need to kill ten Spiderants, five Threshers, and five Crystalisks.

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All of the optional enemies you need to kill can be found in Caustic Caverns.

Luckily, you will likely come across all of these while going for the four pieces of evidence, all of which are marked on your map. One piece of evidence is close to the entrance, near all of the Varkids, while another can be found in the Infested Warehouse area. The other two will be in the Guardian Ruins and Dahl Deep Core 06 areas. For that last one, you will likely pass through the Nether Hive area, which is where you’ll find the Spiderants. Once you have all four pieces of evidence, return to Hammerlock to finish.