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No. 8: Fall 1979

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Convergent evolution or chance look-alikes

Why should caddis fly larvae and a species of aquatic snail look alike? Mimicry is rather common in nature for it often confers some sort of advantage to one or both of the species in the turmoil of evolutionary pressures. Or so the theory goes. Most examples of convergent evolution involve closely related species. In the present case, though, the species are in different phyla. The caddis fly larva builds its snail-like shell by cementing grains of sand together with a silk-like secretion, while the snail's shell is a calcareous excretion. One would expect a strong advantage to be conferred on one or the other species, especially in the matter of predation. Using brook trout as predators, how ever, proved perplexing, for the trout would eat only the snails, avoiding the carbon-copy larvae.

(Berger, Joel, and Kaster, Jerry; "Convergent Evolution between Phyla...." Evolution, 33:511, 1979.)

Comment. This is a remarkable case of mimicry. One wonders how the caddisfly larvae know exactly what snails look like, and how the unique shell constructing methods were coded into its genes by evolution. Or did the snail emulate the larvae?

From Science Frontiers #8, Fall 1979. 1979-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:


  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987