Metamorphosis…

I know, you are probably thinking of The Metamorphosis by Franz Kafka. It is a great story in which a travelling salesman named Gregor Samsa wakes up one day to discover that he has turned into a giant cockroach. It is a very good, short read and I recommend it. Project Gutenberg has it as a free download (along with about 50,000 other titles).

The title of Kafka’s novel is sometimes translated as ‘The Transformation‘ and that is a good word to describe metamorphosis. In biology metamorphosis refers to a significant change in body design occurring after birth or hatching. There are lots of examples but perhaps the most famous is seen in the life cycle of a butterfly. Butterflies start as eggs, hatch into caterpillars (larvae), feed furiously before forming a pupa (or chrysalis) and then emerging as the adult butterfly.

The image to the left shows the different stages in the life cycle of the monarch butterfly. The eggs hatch and caterpillars emerge. These feed until they are ready to form a chrysalis. They undergo metamorphosis and emerge once more as adult butterflies. House flies go through a similar process with egg, then maggot, to chrysalis (called casters by anglers) before emerging as the adult fly.

Some amphibians also undergo metamorphosis. Frogs and toads initially hatch as tadpoles with tails and gills but no legs. As they grow they develop legs but lose their tails and external gills. Newts, which are also amphibians, are not considered to undergo true metamorphosis because they are predators from birth and continue to be throughout their life.

The changes that salmon experience as they move from fresh water to salt water, in their long migration to Arctic feeding grounds, are also considered to be metamorphosis. Although the physical changes are less easy to observe they are quite profound. Normally if you placed a fresh water fish into salt water, osmosis would make water in the fish flow out of their body, killing the fish. Likewise, if you place a sea water fish into a fresh water lake, one of the effects would be the fish swelling up with water as it entered the fish. You can read more about osmosis here.

The BBC has a few clips dedicated to metamorphosis. There is also a good page at Britannica.

Questions…

1. To which class of arthropods do cockroaches, butterflies and house flies belong?
2. Name another class of arthropod and one characteristic they share.
3. What are the five classes of vertebrate?
4. What is the main life process carried out by the larval stage of a butterfly’s life cycle?
5. Suggest one way in which an amphibian differs from a reptile?
6. Suggest an organism, not mentioned in the passage above, that undergoes metamorphosis.