If safely documenting a single hornet sighting without a photograph, what descriptive information is useful for experts?

Answer

Size relative to a common object and the precise time of day.

If a photo cannot be obtained safely, making a mental note of the hornet's size relative to something common and the precise time of day aids experts in surveying the area and predicting foraging patterns.

If safely documenting a single hornet sighting without a photograph, what descriptive information is useful for experts?
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