The Atlas Moth Chronicles
Episode 2 : The Transformation is Complete
A batch of Atlas Moth eggs - usually pinkish in colour
Dr Wee is back to share with us his meticulous up-close-and-personal documentation of the metamorphosis of the Atlas Moth from egg to adult.
The unexpected arrival of a pair of Atlas Moths
) at my porch left me with about 250 eggs.
These eggs were transferred to the leaves of Limau Purut (Citrus hystrix
) branches held in vases.
The rearing of this batch of eggs was to be a learning process. Many failed to survive during the 60-70 days period before pupating. Only four caterpillars survived to turn into pupae and of these only two successfully eclosed. Fortunately the moths that emerged were both females. They attracted males and mated to produce a second generation of eggs. The mating pairs had to be caged as otherwise they would fly off with the females laying their eggs elsewhere.
A caged female Atlas Moth lays her eggs after mating
These eggs, double the number of the first batch, made it necessary to use additional alternative host plants like Starfruit (Averrhoa carambola) and Blue Mahang (Macarange hyeni). My Limau Purut tree would not be able to support this larger number. The caterpillars developed well with all the plants and allowed further observations on their development that were missed during observations on the first batch. These second generation eggs eventually gave a total of 18 pupae.
Maintaining and observing these caterpillars were a full time job. Their voracious appetite demanded daily, or sometimes twice daily, provisions of new branches of their food plants. The water in the vases needed regular changes - after all I was breeding moths, not mosquitoes!
1st instar Atlas Moth caterpillars just after hatching from their eggs
Within nine days most of the eggs hatched into 7 mm grey-white caterpillars with black heads. Projecting from each segment was a ring of tubercles, the tips covered with a tuft of black hairs. The first thing these tiny caterpillars did was to eat up the eggshells. As they grew, they moulted at regular intervals and produced small pellets of frass. These pellets were colourful among the caterpillars feeding on Starfruit leaves, brown on Limau Purut and darker brown on Blue Mahang. Frass of older caterpillars failed to show such differences in colour.
Atlas Moth frass. Clockwise from top left - on Starfruit, Limau Purut, Mahang, and frass of older caterpillars
Moulting Atlas Moth caterpillars
It was relatively difficult to spot the early moulting as the process lasted a few minutes and the emerging caterpillar immediately ate up the discarded skin, leaving no traces. However, with later moults, the caterpillars did not to eat the old skin, or if they did so, they took their time, thus it was relatively easy to spot them.
The second instar caterpillars had a distinctly different appearance from the first - white with patches of orange all over and an orange head. The third instar caterpillars showed a pair of anal claspers each with a distinctly large orange spot. The body remained white with patches and tiny spots of orange that disappeared with age. Older caterpillars turned white with grey-green spots and a light green ventral surface. The final instar caterpillars took on a darker green colouration.
Various instars of the Atlas Moth caterpillars
Moulting was documented during the final moult. The skin suddenly appeared dried and wrinkled. The old skin then turned white and translucent]. Contracting and expanding its body continuously helped the caterpillar separate the old skin from the new. Further vigorous movements caused the old skin to split around the anterior end. All this time the caterpillar was firmly attached to the twig with the help of the anal clasper. Wriggling and forward movement with the help of its prolegs helped it move out of its old skin to eventually leave it behind. The entire process took less that half an hour.
Exactly when the caterpillar molted varied with the individuals, some occurring earlier than others. It took 50-57 days for the first batch of caterpillars to start pupating from hatching and only 38-52 days in the case of the second batch.
As mentioned earlier, the first batch of caterpillars ended in four pupae of which two successfully eclosed. With the second batch, there were 18 pupae and all eclosed.
When a caterpillar had grown to its full size after weeks of intermittent feeding, it rested for some time before proceeding to the next stage of its metamorphosis. It then voided its stomach content, a greenish liquid containing numerous tiny pieces of undigested leaves. The caterpillar then became restless, moving about the twigs for up to 36 hours, apparently in search of a suitable spot to pupate. This, of course was under “culture” conditions. We do not know what happens in the wild.
Pupating sequence of an Atlas Moth caterpillar
Pupae of Atlas Moth cats on two different host plant leaves
Once the caterpillar was satisfied with the spot, it moved its body sideways, spreading a layer of silk on the leaf surface . At the same time it spread silk around the leaf stalk and its attachment to the twig. This was to ensure that the leaf it was pupating on would not get detached from the twig before eclosure. Only then did the caterpillar begin to create a silk cover over itself. The completed pupa on a Limau Purut leaf was a neat elongated structure, 6-7 cm long and 2.5-3 cm wide. With the compound leaves of Starfruit, a number of leaflets would cover the pupa.
Sometimes the pupating caterpillar discharged a liquid that dripped from the bottom of the pupa case. It would be another 22-29 days before the adult moth appeared.
Trying to catch the moment of eclosion was elusive to say the least. For three weeks my vigil was long and tedious, sometimes even sleeping with the pupae by my side. After all, eclosion can happen any time of the day or night. And exactly how many days to eclosion varies. The first two pupae from the early batch of caterpillars eclosed after 25 days. Knowing this did not help as those from the second batch developed a few days earlier. However, having 18 pupae to keep track with was helpful.
The first three eclosions of the second batch occurred during the early hours of the morning, probably between 0400-0500 hours. The fourth pupa took me by surprise when it eclosed during the evening. After four failures I got lucky with the fifth. It also happened in the evening. I was watching the pupa. There were scratching sounds from within. Unfortunately in a moment of inattention the emerging moth simply crawled out of the pupa case in less than a minute. I missed the crucial moment of emergence but managed to document the subsequent sequences.
I was successful in catching the emergence of the adult moth on video only with the ninth pupa. The process was long and tedious as the apical opening of the pupa case was apparently a little too small. The entire process took 6 minutes and the moth then hung from the bottom of the case until its wings were fully expanded.
The next eight pupae eluded me as eclosion came mostly in the early morning, with two in the evenings. However, a second successful encounter came with the last pupa where the adult squeezed easily through the small opening of the silken case in less than 3 minutes.
Since my first encounter with Atlas Moths in 2004, I have been obsessed with finding out how the adult moth emerges from the pupa case. So finally I have satisfied my curiosity and I have two video clips to show for it.
Once the adult moth had emerged from the pupa case, it crawled down to the lower end and hung out its wings as fluids from its abdomen were pumped through the veins until the wings became fully expanded. This can take up to two hours before the wings were fully expanded and functioning.
The next episode will reveal what happened to the emerging adult moths…
Stay tuned for the final episode!
Text & Photos by Dr Wee Yeow Chin