Cobweb Spawner

I am trying to make my spider boss, when all of the sudden when the spawner runs me over.

I have made a Cobweb Spawner, this spawner makes Cobweb as an entity falls down and shall make 1 Cobweb block, but nooo. It makes 1 Block and 3 Wobweb items...

Anyone have a fix for this?

I have tryed to /gamerule doTileDrops 0
but nothing works!