How do I get rid of catepillars on my deck?

Well, to stop them completely would not be possible. The wind will blow some there, even if you treat the deck. Malathion sprayed onto the deck will deter them. HOWEVER, this is toxic and you can't go barefoot, have dogs, children etc. on the deck without danger. If none of those are present. follow the manufactures application instructions and repeat when ever it has been rained off. this is dangerous stuff but will work.