Aluminum pie pans work well. Before visiting the park, call the education coordinator for advice on where to find a fallen, rotting log to study. Then on your park visit, take the students to the log. Remind the children that the log is home to many animals, so they need to be especially considerate of them. Also caution them to always look before they put their hand anywhere.
Warm days are best, as many insects become dormant in cold weather.
If possible, divide your class into several smaller groups, having each group take turns at the log, or visit different logs. Have each group kneel around the log with their eyes closed. Ask them to use their other senses to explore the log. Then ask the children to listen carefully to the log. Have them tap the log in different areas.