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.

Cocoon in Bird Nest Fern
There are about a dozen of these things in that one fern near the Camphor tree

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!

Cocoons in Bird Nest Fern
Notice the bare Camphor tree in the background…

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!

Posted by:Andy Giger

Andy is the Science Centre Singapore's Director of Strategy. He is a Neuroscientist who started out studying how Tunisian desert ants navigate, then tamed honey bees to find out more about their visual system, and moved on to counting cockroaches, feeding termites and attracting mosquitoes. Now he deals more with people, and enjoys being in touch with science on a much broader basis.

4 replies on “Today’s Discovery – Shake it, pupa, shake it!

      1. Not advisable, Danny. I just learnt from someone else’s experience that if shaken too much, there might be liquid oozing out, and that the pupa will break out of the cocoon and die…

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      2. Indeed, it isn’t a good idea to shake the pupae!

        I didn’t shake them, anyway – I just gently turned them to have a look. Then they shook themselves inside their cocoons!

        But triggering that too often is probably not too good for them either, so it’s best to let them rest…

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