Bug Hunt is a new mode in the game that pits up to four players against waves of incoming xenos and enemy soldiers across three new maps: Broadside, Mercenary, and Tribute. You can earn money on the map by killing enemies, and then spend that money to open up extra areas, or buy more guns, ammo, or health.
If you invested in the Season Pass for the game, you'll get this DLC for free. Everybody else has to pony up the equivalent of around $15, though Steam has the game itself on sale for 33 percent off.
Careful, as fighting giant monsters with acid blood in cramped quarters might be exactly as fun as it sounds.