Could it be Galactic Adventures?
One thousand of each type should suffice to clean out our Zwargs' nest for us. Half-an-hour later, Zebekee's preparations were ... Screeching with fury, the Zwargs fought ferociously as their stronghold was invaded on all four sides. .. [from Google Books]
The Google Books page has little bibliographic info (a 1980 pubdate and a partial table of contents). The ISFDB page says it was published by Rand McNally in 1980 (and has a different cover).
The three stories are, respectively, "The Null-gravity Beam" by William Hall, "The Children" by Malcolm Hulke, and "Return of the Warriors" by John Grant.
