**Explanation:**

**Soldier Ants Guard the Grubs**

Grubs are the larvae of ants and other social insects. They are soft and vulnerable, making them a valuable resource for the colony. Therefore, it is important to protect them from any potential threats.

**Role of Soldier Ants**

Soldier ants are responsible for defending the colony against intruders and protecting important resources, such as the queen and the brood (including the grubs). They are larger and have stronger mandibles compared to the worker ants, which makes them better equipped for defense.

**Physical Characteristics**

Soldier ants have large heads and powerful jaws that they use to bite and pinch intruders. They also have strong exoskeletons that provide protection against attacks. Their size and strength make them effective guardians for the colony's grubs.

**Formation of Defensive Line**

When a threat is detected, soldier ants quickly respond by forming a defensive line around the grubs. They position themselves in strategic locations, often near the entrance or in tunnels leading to the brood chambers. This formation creates a barrier that prevents intruders from reaching the grubs.

**Behavioral Adaptations**

Soldier ants exhibit certain behavioral adaptations that enhance their ability to guard the grubs effectively. They are highly alert and responsive, capable of detecting even subtle vibrations or chemical signals indicating potential danger. They communicate with each other through pheromones, allowing them to coordinate their defensive efforts efficiently.

**Cooperation with Worker Ants**

While soldier ants primarily guard the grubs, they work in conjunction with the worker ants to maintain the overall security of the colony. Worker ants assist the soldier ants by reinforcing the defensive line and providing additional protection when necessary.

**Conclusion**

In conclusion, soldier ants are responsible for guarding the grubs in an ant colony. Their larger size, stronger mandibles, and defensive behavior make them well-suited for this role. By forming a defensive line and working together with worker ants, they ensure the safety and survival of the vulnerable grubs, which are essential for the colony's future.