The pitchers accumulate vast quantities of insects in the course of a season, and must thus abundantly manure the surrounding soil when they die.
Not to speak of insects which feed upon the pitcher itself, some drop their eggs into the putrescent mass, where their larvae find abundant nourishment, while birds often slit open the pitchers with their beaks and devour the maggots in their turn.
Siegburg pitchers (Siegburger Krilge) were widely famed.
In most cases such wheels merely have earthenware pitchers attached to their circumference by means of wisps of esparto, and are turned by a horse harnessed to a long arm fitted to a revolving shaft.
- Cephalotus follicularis, showing ordinary leaves and pitchers, the right hand one cut open to show internal structure.