The aliens from across the stars are tired of Gaians coming through the Star Portal to torment them in their Hive. Now they're trying to break out and make a foothold in the Old Aqueduct itself!
To clear the area when aliens come through the Start Portal, they first send through a wave of Deathroaches.
Deathroaches are powerful creatures that will try and touch a specific person, detonating in a biowave of energy, decimating their chosen target. So destroy it at range, run away from it to a safe range, or do anything you can... just don't let it touch you!