And since he asserts that, “when ants die, the survivors set apart a special place (for their interment), and that their ancestral sepulchres such a place is,” we have to answer, that the greater the laudations which he heaps upon irrational animals, so much the more does he magnify (although against his will) the work of that reason which arranged all things in order, and points out the skill which exists among men, and which is capable of adorning by its reason even the gifts which are bestowed by nature on the irrational creation.
But why do I say “irrational,” since Celsus is of opinion that these animals, which, agreeably to the common ideas of all men, are termed irrational, are not really so? Nor does he regard the ants as devoid of reason, who professed to speak of “universal nature,” and who boasted of his truthfulness in the inscription of his book. For, speaking of the ants conversing with one another, he uses the following language: “And when they meet one another they enter into conversation, for which reason they never mistake their way; consequently they possess a full endowment of reason, and some common ideas on certain general subjects, and a voice by which they express themselves regarding accidental things.” Now conversation between one man and another is carried on by means of a voice, which gives expression to the meaning intended, and which also gives utterances concerning what are called “accidental things;” but to say that this was the case with ants would be a most ridiculous assertion.
Source: Against Celsus (New Advent)