Cold Blood Mission
The mission has a soft timer. Beat it before the fourth night, unless you want to challenge yourself (it will be ridiculous).
The little black ant colony can be killed using 19 soldiers and good timing (i.e. sneak in when they move further left to harvest).
The bullfrog can be killed with 80 level 1 soldiers on the second/third day.
You can just ignore the big-headed ant colony on lower difficulty. They only bother you from the fourth day onward.