So far I've never seen the Spidermech Defender do anything. Nothing in the log files, combat chat, or ACT parses. Should it do something and if so should it show up in chat/logs somehow?
Maybe 0.2 of your maximum health is so small it doesn't show up... I know I shook my head when I read the description...
I think one of the recent updates broke it again. Was fixed in https://forums.daybreakgames.com/eq...-thursday-august-10-2017.580174/#post-6455637 but it appears to have stopped working again.