Cold damage spells such as ice spike, will not do damage to any monster without the 'WARM' flag, this includes things like rattlesnakes, giant roaches, and eyebots. Spell damage will 'reflect' off the monster's hide regardless of damage amount.
Cold spells should be intense cold and damage anything and everything.
Traced down to this:
https://github.com/CleverRaven/Cataclysm-DDA/blob/master/src/monster.cpp#L1444
Oddly this does not stop ranged weapons or melee attacks that deal cold damage, just spells.
That cold damage thing seems inherited since more than 6 years ago, I guess it was meant for robots initially.