Respiration: The tracheal triple whammy
All arthropods molt and have an exoskeleton two factors that, as we've just seen, limit the body size of terrestrial animals. Insects, however, got triple-whammied in this department because of the way they breathe. While crustaceans breathe via gills and spiders use gill-like structures called book lungs, insects employ a different system. They get oxygen through tubes called tracheae.