During feeding, they latch onto their slow-crawling prey with their mandibles and secrete saliva that anesthetizes them. Next, external digestion takes place: digestive juices dissolve the food into liquid form, which they consume. Their mouthparts atrophy when they become adults, from then on normally consuming only dew.
螢火蟲幼蟲以蝸牛、貝類維生，覓食時先用大顎將緩慢爬行的獵物咬住，分泌唾液將牠麻醉後，再進行「體外消化」──分泌消化液將食物分解成液狀後再吸食。