Help With Crawling Cicadas Effect (Flash?)

I've got an outdoors related eNews style web page that I'd like to add an effect to, but can't figure out how to do it.
All I'm looking to do is make it appear as though Cicadas are crawling across the user's screen.
Perhaps something in Flash would accomplish this?
Then of course, I'll need to acquire a Cicada image....

Thanks for any help in figuring out how to make this happen!