Gall midges give rise to the "galls" in plants, a swelling that emerges with more rapid growth in particular locations such as the plant's leaf or stem, due to the saliva secreted by larvae of the organism in question. The larvae then feed on the excess plant tissue that forms inside the gall. Each insect species produces its own characteristic kind of gall. These particular midges, which are generally very small, appear with all their same structures in all fossils yet discovered. In other words, this organism never underwent evolution. Another insect whose immutable structures show that it never evolved is the bog beetle. The fossilized amber pictured contains a gall midge trapped alongside a bog beetle.