Avian vs Complete Metamorphosis
Dear Sir/Madam, I have a 3.5 year old daughter who asked me a question
for which I am trying to find an answer. We have got her to understand that the
caterpillar (larva) eats and eats and goes in to pupa (chrysalis) stage before it
gets transformed into a butterfly. We have also got a picture book that explains
the process to her. However, when we tell her that little birds break out of their
egg shell and fly away, she wants to know why she cannot see the "bird caterpillar"
just as she can see a "butterfly caterpillar"? I know this is a rather complicated
question to answer in a manner that a 3 year old can understand. However, I wonder
if you can suggest if there is something analogous to a "butterfly caterpillar".
What an interesting story, I'm delighted to hear you are introducing your daughter
to nature in such a way.
I think you need to make it clear to her that the whole anatomy and life cycle of
insects is completely different from that of vertebrates, so that she does not
confuse them. I don't have any references specific to explaining this to very young
children, these sites may be of some help. Good luck.
Curious daughters demand a response! This question can be addressed in very
complex approaches. I will assume that you will be the one to discuss this with
your daughter so I will not be writing this for her age of understanding.
Insects that use complete metamorphosis such as the butterfly rely on the
caterpillar (larva stage) to feed to provide all the nutrients and energy to grow
(transform) into the adult while within the chrysalis. The adult butterfly is
unable to eat except to acquire moisture and some nectar) sugar from flowers. The
sugar is only an energy source. Most all of the other materials (protein, fats
and nucleic acids) needed to maintain life must be acquired for the adult in the
caterpillar stage of their existence. Most adult butterflies are therefore limited
as to how long they can live as adults; adults exist only for reproduction purposes
anyway. The eggs that are laid by the females are simple in structure because of
her limited resources and can feed immediately and grow as a caterpillar. I am not
going to discuss the insects exoskeleton (outside the body skeleton) which dictates
its small size and limited store abilities.
The Monarch Butterfly is an outstanding exception for it actually migrates to Mexico
during the winters and can survive for several years.
Avians (birds) do not need a caterpillar stage for the mother provides all the
nutrients in the yolk of the egg for the developing bird to grow directly into an
adult. The adult bird can also eat and process all nutrients so their is no need
for a stage to acquire needed nutrients to live and produce nutrient rich egg yolks
to feed the young. The young feed after hatching.
They have means of storing materials in their bodies because they can grow to a
much larger size than insects. This is an evolutionary function of the internal
skeleton. Adult birds can live a great deal longer than a butterfly for these
same reasons. This includes surviving winters which requires a great deal of
energy either in migration or seeking limited food resources in colder climates.
Birds are larger and can store and function better than the insect which is
limited by its small size.
I think this will give you what you need for a 3.5 year old.
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Update: June 2012