Worms on acieed?

Continuing my creepy-crawly-related theme ...  is it possible for worms to become stimulated by caffeine?  Despite a rather vague and, as yet unsuccessful, effort at cutting back on coffee my compost bin still receives a regular fix of grounds.  From last winter's bleak and icy conditions to, a few, hot summer days, every time I open the lid there they are … wiggling in a hyperactive manner.  Have I, inadvertently, got them hooked on a legal stimulant?  They appear to be healthy but noticeably wrigglier than your average worm.

Although I suppose it could simply be an angry protest at having the 'light switched on' …