You’ve gotten to the point where you can differentiate a camelid from a cow, but how do you tell an alpaca from a llama?
Llamas are bigger. While the trend to breed for larger, more robust llamas has gone by the wayside, if a llama and alpaca stand side-by-side, the llama will still be able to look over his smaller, fluffier cousin.
Their ears are different. Llamas have longer, “banana-shaped” ears, while alpacas’ are shorter and straighter.
Llamas have less hair coverage. Alpacas grow fiber on their face and cheeks, and all but the wooliest llamas (or those with alpaca in their background) have cleaner faces.