metamorphose
verb (used with object)
to change the form or nature of; transform.
Used to describe an ongoing action or continuous state that was happening at a specific time in the past.
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Young from the eggs laid in the first week of August were metamorphosing during the last week of August.
From Field Study of Kansas Ant-Eating Frog by Henry S. Fitch