Taxxon evolution is something I've often wondered about, so here's my two cents on the topic.
First of all, Taxxons cannot be purely cannibalistic. If Taxxons ate nothing except other Taxxons, the law of conservation of mass and energy says that the entire population would slowly convert all their mass into energy and then go extinct when they ran out of mass. You cannot have enough babies to offset that trend, because babies do not come from nowhere. So Taxxons might be cannibals, but they are not pure cannibals.
Secondly, book #43 mentions that, while Taxxons are diggers, if they eat nothing but dirt they would starve to death because the dirt doesn't have enough nutrition for them. HOWEVER, the book also says that a Taxxon can lose control and then dig until it starves. This seems like a phenomenally stupid adaptation, since it would mean that Taxxons would be digging themselves to death left and right. Which leads me to believe that it must only be earth's dirt that has so little nutrients that they can starve to death while eating it. Planet Taxxon must have some kind of super-nutrient-rich dirt just so the Taxxons would be able to dig as much as they do without all of them starving to death. And my theory to explain the Taxxon world's "super-dirt" is that the 'scruffy little plants' that Elfangor described in TAC might actually have extensive root systems under the surface, which might enrich the dirt far beyond the levels of nutrients found in earth's dirt.
So, from all this I think I can conclude that the bulk of their diet consists of Taxxon world super-dirt, and that they're hungry all the time because, super-dirt or not, they still need to eat a freaking lot of it to survive. Thus their constant, insatiable hunger is adaptive, since it drives them to eat all the dirt they can. And their cannibalism and hunger for meat is adaptive too, since meat would have even more of the nutrients they need, and thus would be vastly preferred over dirt.
And as far as the hive goes, I believe that it might be the adult form of any Taxxon that actually manages to live long enough to get to that phase, and that the rest of the Taxxons might just be larval forms. Thus why it creates more Taxxons.
