Poop, soil, & the food we eat

Sometimes, while in class, teachers do things they did not anticipate. Today, I planned to review what worms need in comparison to what humans need. After the review, I planned to teach students how to harvest worms. The worms harvested would be traded in exchange for volunteer hours. (I may not be able to pay volunteers in US dollars but trading in my vocation is alive and well.)

During the review of what humans need versus what worms need one of the students asked "Do worms crawl through their poop?" To which I responded, I suppose they do. Although thinking about humans crawling through their own poop sounds pretty disgusting, worms castings are a little bit different because worms have gizzards they grind down "large" food particles. Some of these finely ground food particles are digested into their systems, the rest are excreted and pooped out, creating worm castings. The castings often contain food particles which are likely sensed by the next worm's Prostomium, a sensitive pad located above the mouth which pushes soil out of the way of the worm or pushes food into the worm's mouth. (This comes from my basic understanding, which, admittedly is not very complete or extensive.)

This process is all part of a cycle. Worms, microorganisms, and heat turn poop into soil. In the soil we grow food which is then eaten and subsequently pooped out, which continues the cycle. (This is all rather simplistic but it gets the point across that maybe poop is not really as gross as students initially think.)

What humans need (and some of what humans desire) and what worms need. The lines between indicate commonalities.
Underneath, the cycle of poop, soil, and the food we eat.