To find the length of the beetle in the drawing using a scale of 5:1, you multiply the actual length by the scale factor.
The actual length of the beetle is 1.8 cm. Using the scale of 5:1:
\[ \text{Length in drawing} = \text{Actual length} \times \text{Scale factor} \]
\[ \text{Length in drawing} = 1.8 , \text{cm} \times 5 \]
\[ \text{Length in drawing} = 9 , \text{cm} \]
Therefore, the length of the beetle in the drawing is 9 cm.