Half-Life 2 Larvae Sound Source

Half-Life 2 has some of the most phenomenal video game sounds, and I think I may have found the source of one of them. You know how the Antlion larvae sound in Episode 2? If not, check out this video:
http://www.youtube.com/watch?v=hSRt79unLec

Now listen to the Upland Chorus Frog:

Here’s another interesting frog sound. Although it probably wasn’t used in HL2, it does sound a bit like a Hunter:
http://www.youtube.com/watch?v=QBkNqvpYJOs