When it comes to describing a "big bug," there are several synonyms worth considering. One such word is "beetle," which typically refers to a large, hard-shelled insect. "Goliath beetle" is another phrase that can be used to describe an especially large specimen. "Monster insect" or "giant insect" are also appropriate descriptions, particularly for bugs that are unusually large. Another phrase that may be used is "creepy crawly," although this term is generally more generic in nature and can also refer to smaller insects. Ultimately, the best synonym for "big bug" will depend on the specific type of insect being described and the context in which it is being used.