After a gang of gardners threaten to destroy the patch of forest he lives in, a nerdy ant must work with his insect rivals to build a 6ft tall robot to fend off the human menace and save their colonies.

I'll only add that the inciting incident needs a bit more urgency than the perception of a threat - best you describe the event that made it clear their colony is in danger.

For example:

After a greedy landscaper destroys a nearby patch of forest, a nerdy ant must enlist his insect rivals to build a 6ft tall robot to fend off the menace and save their colony.

Agreed with Richiev, this reads mostly well.

This version of the logline is much better than your previous attempt.

The term, "Gang of gardeners" is a bit clunky, you might consider going back to 'landscaper' or maybe?'greedy landscaper' to give the antagonist a negative?trait.

However, overall this tells us what we need to know.

Using this attempt as a base; here would be a small re-write: (Hope this helps)
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"When a greedy landscaper threatens his patch of forest, a nerdy ant must enlist his insect rivals to build a 6ft tall robot to fend off the menace and save their colony."