Earth creatures

Good Apart from Xen, Race X and Synth creatures, the Half-Life series features Earth creatures as well.

Cockroaches


The Cockroach is an inoffensive creature seen crawling in many places across the Black Mesa Research Facility. Its health is very low, since it only takes to walk on it to squash it. It is unsure if the creature is from Xen or Earth, but as it is seen in the Half-Life Hazard Course, it is likely.

Birds
With the humans, birds are the only known surviving Earth creatures during the Combine occupation, although insects and frogs can be heard in the Canals. No explanation of this is given in-game.

As most NPCs, birds can be killed. Civil Protection officers and Overwatch Snipers can be seen shooting them from time to time, and Xen creatures attack them occasionally as well.

There are three known types of birds in Half-Life 2 and its episodes: the pigeon, the crow and the seagull.

Pigeons
Pigeons (npc_pigeon) are found in the City 17 area and the Canals.

Crows
Crows (npc_crow) are found in City 17, Ravenholm and the Outland.

At the start of the Half-Life 2 chapter Anticitizen One, after Dog is taken away by a Dropship, Gordon proceeds to a building and arrives in the same corridor featured at the very start of the map. Instead of the door leading outside is rubble where can be seen the source of the music: an unplugged television, showing an image of the G-Man standing in a wooden boat with a crow on his shoulder. The television will shut off right after G-Man straightens his tie, and the screen will break by itself when the player gets closer.

False alarms are often triggered in White Forest's secondary silo by nesting crows.

Seagulls
Seagulls (npc_seagull) are found along the Coast and over City 17.

The Fisherman from Lost Coast is very defensive of what remains of Earth's original species. His comments on these species gives the player more knowledge on the effects of Xen lifeforms and the Combine on Earth's natural environment: if the player shoots a seagull, the Fisherman will show he disagrees, saying "Hey, now! We've lost enough species already!", "What'd that gull ever do to you?" or "Don't shoot the gulls! They keep down the leech population!", implying seagulls eat Leeches.

Crabs
In Lost Coast, if the player grabs a crab pot with the Gravity Gun, the Fisherman says that most of the crabs have been eaten by Leeches. That implies some are still alive.

Frogs
Frogs can be heard but not seen in the Canals.

Insects
Insects can be heard but not seen in the Canals and the Outlands.

Rats

 * Rats can be seen at the start of the Half-Life Hazard Course.
 * Concept art suggest they were to be seen with scientists in Black Mesa labs.
 * A rat model can be found in the Half-Life 2 Beta files, suggesting it was to appear in 'Half-Life 2'', but it is not textured.

List of appearances

 * Half-Life: Day One
 * Half-Life
 * Half-Life 2
 * Half-Life 2: Raising the Bar
 * Half-Life 2: Lost Coast
 * Half-Life 2: Episode One
 * Half-Life 2: Episode Two