1) Parts of some cages 
Stenus is a genus of semiaquatic rove beetles in the subfamily Steninae. They are known for swimming by emitting pygidial gland secretions that reduce surface tension and allow them to move on the surface of water. ...
Stenus is a genus of rove beetles, Staphylinidae. There are 72 species of the genus living in Britain, and 114 in Europe, all of a similar appearance with large eyes and a generally dark colouration.