When reading the Voyage, it is impossible to miss the observation that much of the time Darwin was engaged in adolescent boy behavior: Pulling the heads off insects, noting how long they would wiggle after cut in half, closely examining the ooze and guts, occupied much of his time. Obviously, careful observation and a strong stomach were not all that was required to think up Natural Selection and his other theories, or the Origin of Species would have been written dozens of times by dozens of grown up kids.
In the following passages, Darwin is still along the Atlantic Coast, in “The Brazils,” in the general vicinity of Rio de Janeiro, ant it early summer 1832. All of these passages illustrate why insects dreaded Darwin: