1. A dunghill or refuse heap.
2. (Archaeology) A mound or deposit containing shells, animal bones, and other refuse that indicates the site of a human settlement. Also called kitchen midden.
(courtesy of the Free Dictionary)
It's fascinating how the collective actions of a colony of ants - each one of which acts only on simple instincts - produces such a complex structure. In effect, this is an example of how the interaction of a set of simple rules produces complexity that seems to indicate a larger intelligence.
Someone looking at this could come to the conclusion that surely a higher intelligence directed the ants - that ant architects planned this, and ant overseers driected this contruction. They could assume that ants (or at least one ant among them) have higher order intelligence capable of conceiving this, and language that enables them to express and communicate this.
But there isn't. It's the collective actions of many ants, each relating and reacting to the actions of neighbouring ants, that has generated this. We're talking about simple creatures, obeying simple rules, producing a complex result. The words "simple-minded" come to mind, but that's unfair - to judge an ant by human standards of intelligence is to impose a standard on them that really makes no sense: ants are as smart as they need to be for what they do, and, in their context, "smarter" than us. Intelligence is not raw cognitive ability, but is the expression of that ability in a particular context.
We use the word "intelligent" too loosely. Living in an age of computers, we retroactively apply the metaphor and equate intelligence to CPU speeds. We talk of "intelligent design". We assume that intelligence is processing speed, when in reality it's the expression and use of that ability. We might also be tempted to talk about the ant colony having a "collective intelligence", although it's not quite the same as when we use the word to refer to in an individual human being.