Chullin 59a: The characteristics of a kosher grasshopper are that it has four legs, four wings, jumping legs, and its wings cover most of its body. Rav Yehuda said in the name of Rav: This means most of the length of the body. Some say: Most of the circumference. Rav Papa said: Therefore we require them to cover most of the length and most of the circumference.
חולין נט ע”א: ובחגבים: כל שיש לו ארבע רגלים, וארבע כנפים, וקרצולים, וכנפיו חופין את רובו. ובדף סה ע”ב: מאי רובו? אמר רב יהודה אמר רב: רוב ארכו, ואמרי לה: רוב הקיפוֹ אמר רב פפא: הלכך, בעינן רוב ארכו, ובעינן רוב הקיפו.
In approximately 2001, Rabbi Chaim Kanievsky was learning Maseches Chullin and reached the sugyah relating to grasshoppers. Rav Chaim realized that he needed to see a grasshopper to better understand the Gemara, and asked his daughter to bring him one. She tried, but reported to her father that she failed to find one. He went back to the sugyah, and lo and behold, a grasshopper came hopping through the window, landing on his Gemara. After examining it, he let it go. As he continued through the sugyah, he realized that he needed to study the hind legs a bit more, but the grasshopper was long gone. Before closing his Gemara, a second grasshopper hopped in and on to his Gemara, giving him a chance to study its hind legs in detail.
The story spread quickly. Some time later, a rov giving a shiur in Bnei Brak criticized the tales people tell about gedolim, explaining that the stories cannot all be true, and sound silly. As a case in point, he brought the story of Rav Chaim and the grasshoppers. After the shiur, the maggid shiur went home and found his house infested with grasshoppers. He tried for three days to rid his home of the insects, but could not. Someone suggested that he go to Rav Chaim and ask for mechilah. The rov approached Rav Chaim and told him what had happened. Rav Chaim laughed, saying that he did not need his mechilah at all, as the grasshoppers could have come to anybody (after all, the window was open!), and he was certainly mochel him if he needed it. The rov went home – and the grasshoppers were gone!
The above story was printed in a certain sefer, about which Rabbi Yaakov Galinsky quipped, “I would say I don’t believe it, but I am afraid a plague of copies of that sefer will occupy my house.”