Avian Development vs Insect 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".
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 so their is no need for a stage to acquire
needed nutrients to live and produce nutrient rich egg yolks to feed the young.
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.
Click here to return to the Zoology Archives
Update: June 2012