This is actually an erratum for the Core Rulebook, but it relates to the Bestiary.
In the table for Summon Nature's Ally, Ant (drone) is listed for SNA II, whereas Ant (soldier) is listed for SNA III, yet drones are soldiers with a more powerful template added on. Should these be reversed, or should "drone" actually be "worker"?
While we're on the subject of SNA, I'm curious as to why riding dog is SNA I while wolf and hyaena are SNA II. All three are very similar.
It looks to me like the intention was for SNA I and Summon Monster I to summon a regular dog at 1/3 CR instead of the riding dog at CR 1/2. The regular dog would put it inline with the other first level summon spells which all summon 1 HD creatures.
What I cant figure out is why the riding dog is CR 1/2 and the wolf is CR 1. The riding dog has 1 less AC, +1 to hit, +1 to damage, +1 CMB, same special ability of trip on bite, 10 less movement, same HP, and same saves. Seems like they should both be CR 1.
I agree that it looks like the SNA II should have been Ant (worker) since it loses the trip and poison and reduces the Ant (worker) to CR 1. This is inline with the other 2nd level Summon Monster II and SNA II creatures.