This is the perfect example of what educators call a "teachable moment:" a time when an event prompts learning about a new, unplanned topic. In a classroom, the moment may be spurred by an intriguing question asked by a student or a guest who arrives unexpectedly. For science-oriented teachers like me, it may be when something exciting happens in the classroom aquarium such as a crab attacking a mummichog (Challenge: Does anyone know what a mummichog is? If so, post it in the comments!) Or, in this case, some caterpillars decide to move into our garden.
When teachable moments occur in a classroom, teachers usually have a few moments, at best, to decide whether to veer off topic and delve deeper into the new topic or to continue with the scheduled lesson. Ideally, our days would be filled with teachable moments because they represent times when kids are usually highly motivated by the events at hand. The reality is, however, that digging into every teachable moment could lead to a classroom with no focus or one that doesn't reach the required goals for the year. Teachers are faced with the daunting task of choosing those moments carefully.
(Note to educators: I would choose to explore this particular teachable moment with my elementary students because I know I can address many state mandated science and ELA standards along the way. This represents a place where standards and a teachable moment overlap. A win, win all around!)