In four of the egg carton cups, punch a hole with a scissors on opposite sides of the cup. In the remaining two cups, just punch a hole on one side. The cups with just one hole will be the end sections of the caterpillar
Thread the string though the holes in the cups so all six cups are attached in a line. Knot off the string inside the two end cups so it doesn’t come out. When knotting off, leave a little slack in the string so the caterpillar can ”bend” a little bit.
Poke a hole with the scissors in the top of the cup which will be the caterpillar’s head.
If you want to do one of the requirements about mixing primary colors, let the scouts mix some of the paint colors together.
Give each scout a caterpillar and let him paint it.
After the paint dries, have the scout poke the chenille stem into the head so he has two antenna sticking out the top.
Have him twist the chenille stem so the antenna are curly. It might be easiest to let him curl the stem by wrapping it around a pencil.