From Dwarf Fortress Wiki
A giant rat is a rodent of unusual size that is occasionally found in the chasm. They are larger than dwarves and tend to react poorly to claims that they don't exist.
Not to be confused with the large rat.
[CREATURE:RAT_GIANT] [NAME:giant rat:giant rats:giant rat] [TILE:'R'][COLOR:0:0:1] [MODVALUE:2] [LARGE_CHASM][FREQUENCY:100][DIFFICULTY:2] [GENPOWER:2][NATURAL][PET_EXOTIC][MOUNT_EXOTIC] [PETVALUE:500] [PREFSTRING:strength] [BODY:QUADRUPED:TAIL:2EYES:2EARS:NOSE:2LUNGS:HEART:GUTS:ORGANS:THROAT:NECK:SPINE:BRAIN:MOUTH] [SIZE:8] [MAXAGE:2:3] [ATTACK:MAIN:BYTYPE:MOUTH:bite:bites:1:6:GORE][ATTACKFLAG_CANLATCH] [CHILD:1][CHILDNAME:giant rat pup:giant rat pups] [RIVERATTACK:1:1:1:1:1:1][RIVERATTACK_CANUSEWELL] [FAT:3] [ALL_ACTIVE] [BIOME_SUBTERRANEAN_CHASM] [STANDARD_FLESH] [HOMEOTHERM:10067] [LAYERING:100]