The Swarm Egg is an immobile sac of biological matter that incubates a Parasite. The egg can be quickly dispatched with any weapon, but a quick sweeping puff of a Flamer can destroy a group easily with little trouble and ammunition. If not destroyed in time, an egg will expel a Parasite, which can cause panic and result in the large consumption of a Medic's healing items should a Marine become infested. The egg itself can also harm marines who come into physical contact with it.
- Eggs do not start hatching until a marine is in the vicinity, so time can be taken to clear the area of other hostiles before dispatching the eggs.
- A single puff from a Flamer is more than enough to take care of an egg cluster. A Parasite that hatches from a burning egg is harmless and dies quickly.
- Egg sac animations suggest that the Parasite is moving around inside the amniotic yolk.