Elementary, my dear Hopper; Trouble in Bugland: A Collection of Inspector Mantis Mysteries, by William Kotzwinkle. Illustrated by Joe Servello. Boston: David R. Godine. 152 pp. $12.95 . Ages 11 and up.

This amusing collection of five short mysteries is a delightful takeoff on the adventures of Sherlock Holmes and his faithful chronicler, Dr. Watson. There is a difference, however. Inspector Mantis is very tall and very green and has the supersensitive antennae and powerful grip of his namesake. Dr. Hopper, a grasshopper, is a champion long-jumper and plays a mean violin.

They're the residents of Bugland, which looks very much like Victorian England. The two friends live in a cozy flat on Flea Street and ride in cabs drawn by horseflies, all in the pursuit of criminals with such names as A. Stinckbug, Esq. and Mr. Chicken-louse.

The Case of the Frightened Scholar is one of the best. Prof. Channing Booklouse has mistakenly devoured the ''Illustrated History of Bugland,'' containing secret information about the highest workings of the admiralty. The villains in the story want the book and are threatening Professor Booklouse's life. Inspector Mantis and Dr. Hopper have an exciting chase through underworld Bugland and a tussle with a chicken-louse before collaring the criminal, Adrian C. Gallgnat.

Happily, William Kotzwinkle doesn't overdo either the Holmesian touch or the bugginess of his well-written stories.

Joe Servello's colorful, detailed, and abundant drawings of the many legged critters do much to enhance the Victorian atmosphere of the tales.