A new extra level is available now for Empires of the Undergrowth - Extremis. The aim is to survive all the waves - but you won't do it first time. After you die, you are given a number of points (based on how far you got) to unlock new units for your army the next time you play! You might need to reinforce your colony with some wood ant ranged units, or save up for the mighty tanks of the leafcutters!
To find the new level, choose "Other Modes" from the main menu, then "Extra Levels". Please note that your game client will not need to update to unlock Extremis - it will be present in version 0.2131.