Symmetry unveils the biological oddity of animals with organic metal parts:
The metals accumulate after molting, as the animals grow into adulthood. Researchers monitored the percentage of metal deposits at different times during development and observed the channels through which the metals migrate into appendages. They found that different metals settle in different areas: zinc is found in the tips of spider fangs while manganese is found in the trunk.
Including the current survey, metal atoms have been found in 136 species of insects, 30 species of arachnids, 12 species of polychaete worms and four species of centipedes. Even so, there are still thousands of species to examine. Ultimately, researchers hope that understanding this biological pattern found in so many current species will guide the search for a common ancestor.