Animal size in animal spells

A quick, quite silly question after all these many years: do Animal spells need size modifiers, as Corpus spells do, to affect specially big animals?

I thought they didn't because I always keep in mind the example of penetration in the core book, where a maga goes off to cast Agony of the Beast to a dragon after crafting the horoscope of the beast, and there isn't any mention of the spell being a tailored one to affect big beasts. I found it somewhat contradictory against corpus, but hey, maybe it was just that it's harder to affect things that may have souls attached inside. But then I just re-read Panic of the Elephant’s Mouse, and there it says "note that this spell cannot actually affect elephants, as they are too large". So now I'm starting to fear about the penetration example's maga. If I'm right in my concerns about having got this wrong all these year, I hope she realized that she required a modified spell on her way to the dragon's lair...

Yes, they need size modifiers. A standard spell affects up to size +1, but a lot of large mammals are larger so require an extra magnitude. Sea creatures and large supernatural beasts can require more. See the sentence on p117 of the main book "A basic individual for Animal is an animal of about the same size as a pony, size +1 or lower."

The Wizards' Mount, Steed of Vengeance, Blunt the Viper's fangs, The Gentle Beast - all of these include a size modifier to affect larger creatures.

So poor Mari Amwithig. I guess it didn't went as planned after she arrived there with her horoscope and her confident smile, cast her spell on the dragon and then nothing happened.

It's OK, Mari was probably playing in a 5th edition playtest so her SG may have accidentally treated the spell like 4th edition and thought it worked as target: individual in 4th was any discrete object. Alternatively she turned up trying to cast a 4th edition spell and got in trouble for forgetting differences between editions.

Mentem doesn't care about the size of the individual mind that it targets. While I see no similar note concerning the mlnds of animals in the text, a storyguide might reasonably bend the rules to allow an intellego animal spell to probe the memory of a cow without a size modifier.

I wouldn't.
For animals, their bodies and minds are not seperate phenomenae

Hmmm, it just seems a bit odd to me that every animal spell in the core book (except InAn spells) don't work on a common horse (and it makes me think that the designers of the core spells were more worried about wolves than bears or horses). But with the solution being as simple as remembering to add at least one size modifier and cover all sizes up to the elephant's one I think I can live with that.

On both counts.

Some dragons are small (e.g. Arkliss, a Dragon of the Fens from RoP:M, is Size 0).

Meh. If it doesn't turn you into a hamburger just by treading on you, we don't call it a dragon.