You may only take essence from floating essence clouds if you have less than 25 pieces in your inventory, as clicking "Collect" would bring the number up to 25.
When you deplete an essence creature, you will receive 50-150 pieces of essence.
You can also chip an essence creature to obtain small amounts of essence. However, chipping essence from a mind essling requires ten air runes. This allows you to gain more essence than from floating essence so you can siphon for longer without restocking.
If you choose to destroy your rune essence, all of the rune essence will be destroyed when clicking yes, even though there is an all option.
Players that try to bank any runes or essence from Runespan receive the message "A magical force prevents you from banking this item."