**Core Concept:** The larval stages of a housefly (Musca domestica) consist of four instars, each with distinct characteristics. The first three instars are non-feeding stages, while the fourth instar is the most active and voracious feeder.

**Why the Correct Answer is Right:** The correct answer, **Option D**, represents the fourth stage of the housefly's life cycle, which is the feeding stage. In this stage, the housefly larvae are highly active and voracious feeders, consuming a wide range of organic materials, including fecal matter, decaying organic matter, and even human and animal corpses. The other options (A, B, and C) represent the non-feeding stages of the housefly larva, which are characterized by slow growth and minimal feeding activity.

**Why Each Wrong Option is Incorrect:**

A. **Option A**: The first stage is a non-feeding stage called the egg stage.
B. **Option B**: The second stage is also a non-feeding stage, known as the larval cell stage.
C. **Option C**: The third stage is a non-feeding stage called the spinning larval stage.

**Clinical Pearl:** Understanding the life cycle of common insects like houseflies is crucial in public health, particularly in preventing the spread of diseases like anthrax, cholera, and dysentery, as houseflies can transmit pathogens from contaminated fecal matter to human and animal food sources during their feeding activity.

**Correct Answer:** **Option D**. The fourth stage (larval stage) is the feeding stage, where the housefly larvae exhibit voracious feeding behavior. This information is essential for understanding the life cycle of houseflies and their role in transmitting pathogens that cause diseases like cholera, dysentery, and anthrax.