Huh, spiders also did that? When I was a kid, I once caught a cricket and a grasshopper and put them in a shoebox. I put the shoebox under my bed and left them in there over night.
The following morning, I opened it up, and found the cricket hopping around, but the grasshopper was decapitated with a couple of its legs shoved into the neck.
I took the cricket outside and let it go.