Hexagons
Hexagons is a six-sided shape that tiles flat surfaces with no gaps, which is why bees build honeycombs from them.
Think of it this way
A tray of ice cube molds shows this well. Each mold is a six-sided hexagon. Pack them tight and they fit edge-to-edge with no wasted space between them. Bees figured this out too — hexagons hold the most honey and use the least wax.
Explaining hexagons by grade level
Look at a honeycomb. Each cell has six flat sides. The cells fit next to each other with no space left over. No other shape packs this tightly on a flat surface. Bees use this shape to store honey and save wax.
