The spider leaving a corpse makes sense as it doesn't seem to be so much an elemental as it is a creature that earth mages can command. Same thing with the wolf.
Sure it makes sense: you call it, it dies, it leaves a corpse.
But for the sake of immersion and role-playing and all that touchy-feely game satisfaction stuff, if you want to summon a wolf without feeling like a prick, it's hard to be all "Hey, come help me fight! If you win, you'll die a couple of minutes later than if you lose!"
If it's that close to death magic, it should be Witchcraft, not Earth magic/Ranger/some kind of Druidy nature thing. People get attached to dogs.
Hell, there's even an existing script for dogs to run into the woods and vanish; why can't they just have the summoned wolves do that?
I like spiders just fine, too, but I kind of get the feeling that that's less of an issue for most folks.
Addition for clarity:Just so we know where I'll stand when the PETA revolution comes along, can I point out that I really *like* that Bertia is an actual farmer? Sure, she values her animals: they're her living, and they're all individuals. But they're also mighty fine eating with mint sauce. That dialog makes me smile every time.