When I have insects in my home, like spiders or centipedes, I generally leave them be, or sometimes take them outside if guests are worried about being bitten. However, I will kill mosquitos, since they are preying on me, and can spread disease in so doing.
I value the lives of animals highly, and provided one doesn't cause or intend harm, I leave them be. I would fight and potentially kill one to defend my life, happiness, or safety. I'm fine with hunting and killing animals as well, provided it's done to strengthen the life of something or someone else. I believe that killing, done respectfully and for the purpose of survival, is justifiable.
I don't believe in killing as punnishment, because the harm has already been done... to add further death would only make things as a whole worse. I also value human life highly, since humanity is, as a whole, an amazing happening. I also value animal life much the same, and can't condone the purposeless killing of an animal.
If you're looking for an exact value... I'm afraid I can't give that, but Life is an impossibly rare, infinitely unique, and incredibly complex thing. Life, from Bacteria to Bactrian Camel, is one of the most valuable things we have discovered, and it's preservation should be the most important thing we, as individuals, and as a species, can pursue.