This is an easy question to answer. To be blunt, the answer is yes. Do you need proof in scripture, because you are so dull and also so hard headed that you will not accept anything unless it is found in scripture? Just read Matthew 8 and your proof will be found there. Let us read it together.
Matthew 8:
28 When he arrived at the other side in the region of the Gadarenes, two demon-possessed men
[this most likely is just one man versus two, for we already know "Matthew' was not written by
Matthew] coming from the tombs met him. They were so violent that no one could pass that way.
29 "What do you want with us, Son of God?" they shouted. "Have you come here to torture us
before the appointed time?"
30 Some distance from them a large herd of pigs was feeding.
31 The demons begged Jesus, "If you drive us out, send us INTO the herd of pigs."
32 He said to them, "Go!" So they came out and went INTO the pigs, and the whole herd rushed
down the steep bank into the lake and died in the water.
So you see, just by this story alone we can know for sure that demons can possess animals and not just people.
Thomas