Why is the term linchpin appropriate in describing the termites

The term linchpin is appropriate in describing the termites as they are ecologically important for ecosystem. They play different roles.Termites being decomposers digest the cellulose present in the decaying plant matter, they convert cellulose into reusable form for plants. Termites fix nitrogen by digesting the nutrients in the soil and separates the nitrogen from the attached atoms which is easily taken up by the plants. Termites creates shelter for various insects colonies. They burrow deep inside the soil, creates tunnels suitable for insects colonies living.    

your body is trying to warm itself up. or more precisely, sensors in your skin send messages to your brain to generate heat to your body.