The larval predation behavior of two species of firefly, Diaphanes sp. and Pyrocoelia pectoralis, was observed. Larvae of D. sp. preyed on earthworms whereas P. pectoralis preyed on snails. The structures of larval head and mouthparts of these two species were observed with scanning electron microscope. Both two species of firefly had well-developed three segments of antenna and a pair of lateral ocellus. Larval mouthpart was well-developed, and composed of one pair of sharp, hollow and curved mandibles, max palp, lacinia and labial palp. The mandibles were significantly different between two species of larvae. A globular structure with a layer of teeth structure covered on 2/3 inner mandible in D. sp., whereas a large teeth structure on the base of inner mandible found in P. pectoralis.