A partial list of things which scared H. P. Lovecraft—

Sexuality, procreation, the human body, invertebrates, marine life in general, temperatures below freezing, fat people, people of other races, race-mixing, slums, percussion instruments, caves, cellars, old age, great expanses of time, monumental architecture, non-Euclidean geometry, deserts, oceans, rats, dogs, the New England countryside, New York City, fungi and molds, viscous substances, medical experiments, dreams, brittle textures, gelatinous textures, the color gray, plant life of diverse sorts, memory lapses, old books, heredity, mists, gases, whistling, whispering.

See Luc Sante, "The Heroic Nerd", in The New York Review of Books, Volume 53, Number 16, 19 October 2006.