I use water crystals in my pots and vege garden. The vege patch is teeming with earthworms. A veritable plethora of the dark loving subterrainean soil eating little blighters . So i don't reckon they'll mind the crystals. I doubt they'd actually eat them but you never know. They might once they start to break down. The crystals are a polymer. (read plastic)

I've often wondered though, if there were any potential negative effects for we humans so you gave me the impetus to research this.

I found this website which suggests they are non-carcinogenic, which is always a bonus, may cause respiratory problems if inhaled and can cause a skin reaction through contact.
So wear gloves and use in a well ventilated area.

The MSDS sheets are here too if you wanna have a look.
http://www.watercrystals.com/MSDS.htm

Thanks for the urge to research Amber.