Pile of giant mantis eggs
It is a quest item for the first part of Bleed Me Dry. Red Lucy of The Thorn will give you 200 caps for them, or 300 with a Barter check of 50. It spawns once the quest has started and cannot be dropped.
The pile will spawn on the third level of Vault 22 (Food Production), as part of the quest Bleed Me Dry. The eggs will spawn at a dead end in the cave tunnels, guarded by many giant mantises. You will need the Vault 22 cave door keycard to access the area. The marker points out the exact location.
Alternatively, if you have already collected ten giant mantis eggs, they will turn into a pile.