MadSci Network: General Biology

Re: Color of a caterpillar

Date: Wed Oct 31 10:25:37 2001
Posted By: Bela Tiwari, Staff, Bioinformatics Centre, Oxford University
Area of science: General Biology
ID: 1002488517.Gb

>If a caterpillar consume only a certain color of milkweed from food 
>coloring, will its pupa change color?


Thanks for sending in such an interesting question.

I cannot answer your question directly, but I would infer (from the 
information I’ll relate below) that the answer is “probably not”.

Some information:

Insect pupae are usually immobile and are thus quite vulnerable to 
predation. In some insect species protection is afforded by pupation 
occurring within a cell or cocoon. For example, the larva of the Puss moth, 
Cerura, constructs a chamber made of wood fragments; these fragments are 
glued together to form a hard layer within which the pupa develops. Another 
species, the silk moth Antheraea can spin a cocoon of silk within which 
pupation occurs.

However, the pupae of some butterflies, including the Monarch butterfly 
(Danaus plexippus), are not shielded in this way, and the coloration of the 
pupae may be its only protection. By blending in with its surroundings, it 
may be able to avoid detection by predators.

The descriptions of Monarch pupae state that they are blue-green, later 
turning brown, (before the coloration of the maturing butterfly can be 
discerned through the transparent skin of the pupa). They also describe 
characteristic gold spots on the pupa. The only information I could find 
relating the diet of the Monarch caterpillar to the color of its pupae 
involved the role of certain chemicals from milkweed and the color of these 

Monarch larvae feed solely on milkweeds of the family Asclepiadaceae. Some 
milkweeds are rich in chemicals known as cardenolides, and adult Monarchs 
can contain high levels of these cardenolides, which are known to make 
butterflies unpalatable to many predators (for example, many birds).   

Under normal circumstances, D. plexippus (the Monarch) is known to store 
cardenolides. However, caterpillars raised on a carotenoid-free diet produce 
pupae with silver metallic areas instead of the normal gold areas (and 
butterflies that do not contain cardenolides).

Futher considering your question, it is worth asking how, and with  what,  
you would dye the milkweed plant. In order to affect the color of the 
insect, I would think that the coloring would have to be associated with 
some part of the plant is actually taken into the insect and used, 
otherwise, it would probably just be excreted as waste.  It is also worth 
looking more closely at why you want to know the answer. For example, are 
you interested in the way nutrients  are taken up and utilized by the 
caterpillar?  Are you interested in whether camouflage protects the pupae 
from predation?  Something else? If you further define your question, it 
might be easier to either find out an answer, or design an experiment to 
answer the question yourself.

On  the topic of pupal camouflage, it is interesting to note that two other 
butterflies of the genus Danaus, (i.e. related to the Monarch),  D. 
chrysippus and D. gilippus, can match the color of the background they are 
in,  whereas Monarch pupae are always blue green.

I hope this helps. I have listed some of the references I used to find out 
this information  below.


Urquhart, F.A. 1960 The Monarch Butterfly, University of Toronto Press.

Rothschild, M., Gardiner, B.,  Mummery, R. 1978 Pupal Colouration and Diet. 
Antenna, London.  2, 15 

Brower, L.P., 1984 Chemical Defense in Butterflies in Vane-Wright and 
Ackery, The Biology of Butterflies. Symposia of the Royal Entomological 
Society of London, 11. 109-134.

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