Sunday, 26 August 2012

A Mystery Solved

In a previous blog I noted a couple of caterpillars that I would attempt to rear to maturity. Until now the efforts went unrewarded.

We know the identity of one of them.
 To review, I noticed the white caterpillar on tree trunks covered with lichens and algae.
The individuals had an irregular appearance. Dissection of one of them revealed that each was covered with the lichen material that was held in place by threads of silk.

 The caterpillars move with an arching gait and travel up and down the trunk over 2m per day. But they always seem to return to nearly the same place each day.
The caterpillars seem to feed on the white-patch lichens but because of the concealment of the mouthparts, it is difficult to determine if they are feeding on anything else. It's obvious that the caterpillars incorporate some of the green material into their camouflage. Ants and other insects travel past the caterpillars and pay them no attention. 

This year, the caterpillars were found on palm trunks and the trees where they were last year had no caterpillars on them at all.

I took two of the larger larvae and scraped a few bits of lichen off one of the trunks and placed it in a container. After a few days a cocoon was formed.
 The coccoon. Each cocoon was borne on an elongate stem. After 29 days, at room temperature, the moth emerged.
Enispa prolectus (Turner): Noctuidae; Acontiinae

The moth is relatively common and turns up regularly at the light sheet. Seven species of Enispa are known from Australia. It seems that little is known of their habits. Common (1990) records one species, E. plutonis (Lucas), living in spider's webs where they feed on the detritus such as dead leaves and the left-overs from the spider's catch. The caterpillar is naked and not covered with any detritus.  Its pupa is suspended without any cocoon by its anal hooks. This is very different from E. prolectus. With E. prolectus, there is a cocoon that is suspended on a stem which is firmly attached to the substrate by silk.

The next step is to find the distinctive cocoons in the habitat. They most likely move to adjacent vegetation or, perhaps, under loose bark. This is in short supply on rainforest trees.

Thanks to Buck Richardson, and his moth identification site, for aid in identifying the moth.

Literature

Common, IFB. 1990. Moths of Australia. Melbourne University Press. Pp. 1-535.

4 comments:

randomtruth said...

Excellent detective work. And a lovely prize at the end.

Camera Trap Codger said...

That is really cool.

Mr. Smiley said...

Thanks folks
D

Cooper Creek Wilderness said...

Well done David and thanks for sharing!