I like to make discoveries – making an observation and figuring out something I didn’t know before. Quite often, this happens in our Ecogarden. Like today, when I checked on the Atlas Moth pupae that have caused quite a stir among some of our staff here at the Science Centre.
All those remaining caterpillars still roaming around the almost bald Camphor tree the last time I visited had obviously moved to the neighbouring Bird Nest Fern to find a suitable support to pupate on.
Lifting one of those big fern leaves to examine the cocoons attached to it, I noticed a rhythmic knocking in the leaf. At first, I thought the leaf was rubbing against another leaf, or the wind blowing across it caused it to vibrate. But the knocking was too distinct, and I started to suspect that it came from the cocoons.
Some further experimentation – lifting other leaves without cocoons, lifting other leaves with cocoons, turning the same leaf at different angles – soon confirmed: the pupae were shaking inside their cocoons!
Whenever the angle of a cocoon was changed significantly – eg by me turning a leaf to look at the cocoon on its underside – the pupa inside must have twisted back and forth or knocked on the walls of its enclosure some other way. All I know is I could feel the knocks in the leaf, something that might be startling enough to deter a would-be predator, I guess.
Once I had confirmed that to myself, I didn’t touch the fern any more – we don’t want to stress our metamorphosising friends too much!