An arthropod that is destructive at early stage of its life cycle is

Analyze the question: We need an arthropod that is destructive (a pest) in its early life stage, meaning the larva or juvenile stage.

Concept: Insects such as butterflies and moths undergo complete metamorphosis: egg → larva (caterpillar) → pupa → adult.

• The larva (caterpillar) is the feeding stage. It eats leaves, stems and crops voraciously. Examples include the armyworm and the cotton bollworm, which are caterpillars of moths and butterflies.
• The adult butterfly feeds on nectar and is generally harmless. It even helps with pollination.

Checking each option:

• A. Butterfly: The caterpillar destroys crops and leaves, so it is destructive at the early stage. The adult is not. ✔
• B. Mosquito: The larva (wriggler) lives in water and feeds on microorganisms, so it is harmless. The adult female is the harmful stage, since she transmits malaria and other diseases. This is the opposite of what the question asks.
• C. Bee: Bee larvae are fed and cared for in the hive and cause no destruction. Adult bees are useful as pollinators and honey producers.
• D. Millipede: It is an arthropod, but it has no larval metamorphosis. The young look like small adults and it feeds on decaying matter, though it may occasionally damage seedlings. It is not the best fit.

Answer: The butterfly, because its larval stage (the caterpillar) is the destructive stage of its life cycle.

Exam tip: Remember "caterpillar = crop destroyer". For the mosquito, remember "adult female = disease carrier". Questions on destructive stage usually test whether you can separate larval pests (butterfly/moth) from adult pests (mosquito, locust).