What is the name for a fly that mimics a larval fly when fly fishing?

The term for a fly that mimics a larval form when fly fishing is "nymph." Nymphs are essential in the life cycle of aquatic insects, representing the immature stage before they emerge as adult flies. When trout or other fish are feeding underwater, they often target nymphs, making these patterns effective for enticing fish during this stage of the insect's life cycle.

The other options serve different purposes in fly fishing. A dry fly is designed to float on the water's surface and imitate adult insects, while a streamer is meant to mimic baitfish or larger aquatic prey, often fished with a different technique. The Woolly Bugger is a versatile fly that can represent various aquatic creatures but does not specifically mimic a larval fly in its standard use. It is typically associated with more active presentations rather than the subtle approach of nymphing. Thus, the correct identification of a nymph as a larval imitation captures a key aspect of the feeding behavior of fish and the techniques employed by anglers.