A big mantis will eat small lizards and birds, but a small mantis will be eaten by larger birds and lizards. I didn't see my first one until about 10 years ago while we were visiting Utah and didn't even know what they were. Apparently Montana and Wyoming are too cold for them to survive. I was freaked out when I first saw one but now I think they are fascinating and I rather like watching them. They have voracious appetites where flies and grasshoppers are concerned so we welcome them to our yard.
Here is a link to see what they are all about. There is a really good photo of one here.
Praying Mantids, Praying Mantis Pictures, Praying Mantis Facts - National Geog