Swarms also appear in the spin-off game Silent Hill: Book of Memories.
Swarms are large, beetle-like creatures with a flexible, leech-like mouth. They have shiny black exoskeletons and large wings with which they use to hover in front of Alex Shepherd before attacking. A Swarm's legs are each edged with sharp ridges, which it will use to assure it achieves a firm latch onto Alex. This explains why removing one can be tedious.
Swarms attack by latching onto Alex and draining his blood. They hover in the air for a moment before latching onto him, during which time Alex can attack and kill them. Otherwise, while they're on the ground he can stomp on them. Once latched on, they will continue to drain his health until he removes them with a "dodge" action. They perish with one hit from any weapon.
They are a mixture of leeches and roaches, which are both common pests in times of war, especially in humid areas. However, they can also represent the decay of Shepherd's Glen and the rotten insides of the town's origins, and the perceived evil of Silent Hill, Maine invading Shepherd's Glen. The leech element in particular points towards lakes, rivers, and other bodies of water, where leeches are common, and in turn the events that occurred on Toluca Lake.
Swarms may also be reminiscent of Joshua Shepherd's fascination with bugs in general. It is also possible that the Swarms represent the memory of Joshua's death prying at Alex's subconscious. This is supported by how they will attach onto Alex and drain his blood, therefore making them a parasitic organisms. Just as well, bad memories that fail to vanish are often described as being "parasitic", as they drain the "host" of liveliness and the will to continue on normally through life. It's also very important to note how Alex must immediately repel a Swarm, seeing as otherwise he gradually dies. Alex's behavior of throwing Swarms aside can be symbolic of how he has completely buried the memory of his younger brother's death.
- Defeating a Swarm for the first time while playing on an Xbox 360 will award the player with the achievement "Creeper Reaper". This is a reference to the Creeper of Silent Hill and Silent Hill 2. Both monsters have very close similarities.