In the huge, crisp cocoon, extraordinary processes began.
The caterpillar’s swathed flesh began to break down. Legs and eyes and bristles and body-segments lost their integrity. The tubular body became fluid.
The thing drew on the stored energy it had drawn from the dreamshit and powered its transformation. It self-organized. Its mutating form bubbled and welled up into strange dimensional rifts oozing like oily sludge over the brim of the world into other planes and back again. It folded in on itself, shaping itself out of the protean sludge of its own base matter.
It was unstable.
It was alive, and then there was a time between forms when it was neither alive nor dead, but saturated with power.
And then it was alive again. But different.
~ Perdido Street Station, China Miéville
The larva encases itself in a chrysalis or cocoon and enzymes begin to break down its tissues. Eventually all that is left of the original larva are clusters of cells known as imaginal discs. The digested tissue from the remainder of the caterpillar supplies nutrients to the imaginal discs which rapidly grow and differentiate into the wings, antennae, legs and other parts of the adult butterfly. The adult emerges from the chrysalis fully formed.
Amazingly, a recent study has shown that behavior learned as a larva can be retained in the adult, suggesting that the neurons involved in memory also survive metamorphosis and are integrated into the adult nervous system.
There are a number of hypotheses to explain how such a complicated system might have evolved. But the oddest hypothesis comes from zoologist Donald Williamson , who suggests that the larval caterpillar and adult butterfly evolved from two completely different organisms, whose genomes somehow fused together. He proposes that the transformation of a caterpillar into a butterfly is more one creature turning into another, than a juvenile turning into an adult.
Williamson’s idea has been pretty thoroughly debunked in light of what’s known about butterfly and moth biology and evolution. It’s especially hard to explain in light of the experiments showing the persistence of memory through the process. But I think it’s a great science fictional idea.
In Orson Scott Card’s Speaker for the Dead the alien Pequininos (or piggies) go through metamorphosis from animal to plant, which never seemed very biologically plausible to me.
So are there good science fiction examples of hybrid lifeforms that shift from one to the other during their lifetime? What do you guys think?
- Inside the Chrysalis by Dr. Lincoln Brower
- Erezvilmaz DF “Imperfect eggs and oviform nymphs: a history of ideas about the origins of insect metamorphosis” Integr. Comp. Biol. (2006) 46 (6): 795-807.doi: 10.1093/icb/icl033
- Douglas J. Blackiston, Elena Silva Casey & Martha R. Weiss (2008). “Retention of memory through metamorphosis: can a moth remember what it learned as a caterpillar?”. PLoS ONE 3 (3): e1736. doi:10.1371/journal.pone.0001736.
- Williamson DI. Caterpillars evolved from onychophorans by hybridogenesis. Proc Natl Acad Sci USA.2009;106:15786–15790 doi:10.1073/pnas.0908357106
- Hart MW and Grosberg RK “Caterpillars did not evolve from onychophorans by hybridogenesis” Proc Natl Acad Sci U S A. 2009 November 24; 106(47): 19906–19909. doi: 10.1073/pnas.0910229106
Top image: Manduca sexta (tobacco horn worm) larva devouring a tomato plant in preparation for metamorphosis. Photo by me.
Bottom image: Adult butterfly, species unknown. Photo by me.