What about insects?
I include insects in my animal rights philosophy. I try to avoid accidentally stepping on insects. Also, when I find an insect in my home, I try to carefully carry the insect outside without injuring him.
With regards to animal rights, the distinguishing characteristic between plants and animals is that animals possess consciousness, whereas plants do not. Although I can not prove it with absolute 100% certainty, I believe that at least certain insects are also conscious. By this, I do not mean that insects discuss philosophy, but simply that they feel sensations such as pain and hunger. For this reason, I believe we should include insects in our sphere of compassion.
It is true that regardless of how hard we try, we are inevitably going to accidentally kill some insects during our lifetimes. It is also true that regardless of how hard we try, some people are going to be killed in car accidents. However, the fact that we might run over someone with our car by accident does not imply that it is ok to run them over on purpose.
Follow up questions:
What do you do when a colony of insects infests your home?
Do you view the killing of an insect as the moral equivalent of killing a bird or mammal?
Don't insects only behave on an instinctual level?
Do ants recognize their reflection in a mirror?
How do you know that plants can not feel pain?