Originally Posted by
Alric
In terms of useful and practical things you could of done, the order goes something like this from most useful to least...
1. Give the spider medical care to save it.
2. Leave some food for it, so if it survives it can eat even while wounded.
3. Leave it and hope it survives.
4. Put it out of it's misery.
5. Ask the spider for forgiveness.
6. Ask the spider's soul for forgiveness after it died.
7. Pray to Jesus to forgive you.
The first one would be optimal, though it depends on how hurt it was and your knowledge of spider anatomy and or how close you are getting help for it. The second may actually help if it survives, and so your increasing it's survival chances. Three is probably what most would do, 4 kills it but ends it's suffering so while it isn't as good as saving it, it might be something. It is unlikely a spider will understand you if you ask for forgiveness and this option is pretty useless but in the off chance it can kind of pick up on the inflections of your voice it might kind of sort of understand on some level, though probably not, it is just a spider. Spiders probably don't have souls so the next option is probably entirely useless but at least you are trying something, even if it is useless. The last is utterly useless though. I don't believe in the Christian god, but even if you did he clearly doesn't give a shit about a spider.
If you want to do something nice for the spider after the fact, the only real thing you can do is hold it in your memories so it isn't forgotten in this world, and then maybe be more careful in the future so you don't accidentally kill other ones.