Ants certainly have a circulatory system where fluid is distributed by means of a pulsating sac of some sort. They do not pump blood like ours though and they obtain oxygen directly from the air through tubes called spiracles [spelling?].
And thats why 1950's B-movie style huge monster insects do not exist, this method of respiration ceases to function once the insect reaches a certain size, ie some of the big tropical spiders that are several inches wide but no more.