Other species, like the newly discovered Pheidole drogon, have evolved to grow spikes or spines from their exoskeletons. (How these ants help find fossils.) One Amazon species (Allomerus ...
In 2003 I completed a study of the "big-headed ants" of the Western Hemisphere, a genus (Pheidole) that has the largest number of known species and is among the most abundant of all the ants.