The thieving locust card (team) is one of the Gorajo cards a player can be given by the Gorajo hoardstalker found in the resource dungeon in Meilyr Clan district in Prifddinas, requiring level 95 Dungeoneering to enter. You can get one card per day from the hoardstalker, resetting at 00:00 UTC. This version of the card affects every member of the Dungeoneering team, and there is a solo version of the card that only works for the player who activated it. You can only have one solo card and one team card (of any type) at once.
To use this card, start a dungeon at Daemonheim, and click to activate it, consuming it. For all members of the dungeon party, it doubles the experience awarded at the end of the dungeon. This stacks with the preening ibis card, but does not increase the number of Dungeoneering tokens rewarded.