Found the problem with the fire beetles.
Unlike most pets, the documented statistics for fire beetles indicate that their minimum and maximum hit points, strength, dex, and int are the same. There is no range (at least not according to Stratics and the old Vetmaster data).
The power formula uses the difference between the min and max possible ranges, and YOUR pet's comparison to those ranges, to generate the score.
I could remove fire beetles from the tool, since they don't abide by the same rules as other pets, or...
To give a more accurate reflection of the fire beetle's score (since its data seems to differ from the stats of other pets in UO), I've input minimum data that is comparable to that of other pets (by comparing other pets' average difference between their min and max values for hp, str, dex, and int). So, the calculator now gives an accurate score (relative to scores for other pets).
I'm not sure why fire beetles are so locked into one set of stats, whereas other pets have ranges of stats... odd! Note, though, that the min ranges I input are not accurate to the actual minimums you'll find in the wild - but fire beetles don't fit the mold, so to speak, and this was the only way to give them a score with this calculator. It is comparable to other pet scores, though, relatively speaking.
Hope that helps! If anybody sees a problem with a pet, please feel free to PM me here or on UOForums or via email (available on the UOCraft.com web site or in my profiles).
PS - I plan to add battle chickens soon!