That was my first impression. But then I thought in humans, and concluded ants have less muscle % of volume

Less muscle than us by ANY measure would be mindblowing for beings who can carry up to 100 times their weight, compared to ~ 1-2 we can.

I can't give any appreciation of muscle % of weight. I don't know how heavy is chiting armor/exoskeleton.

specifically head, and it is that big for that reason. I mean it is logical, yet i have never even thought about that until seeing those images. They are basically working and killing machines.