Great Diving Beetle (Dytiscus marginalis), showcasing the physical differences between the male and the female of the species 插畫檔

As noted in the caption of your image, these are the male and female forms. You can tell them apart by looking at their wing cases (elytra) and front legs:The Male (Left):Smooth Elytra: His wing cases are smooth and shiny.Suction Cups: He has specialized, circular "sucking discs" on his front legs. He uses these to hold onto the female during mating, as her back can be quite slippery underwater.The Female (Right):Grooved Elytra: Her wing cases have deep, longitudinal furrows or grooves (sulci) that run about two-thirds of the way down her back.Normal Front Legs: She lacks the large suction discs found on the male.About the Great Diving BeetleSize: They are among the largest freshwater beetles, typically growing to about 27–35 mm in length.Habitat: They are common in ponds, lakes, and slow-moving streams throughout Europe and northern Asia.Diet: Both the adults and their larvae are fierce predators. They eat other insects, tadpoles, and even small fish.Breathing: Although they live underwater, they breathe air. They trap a bubble of air under their wing cases and carry it down with them like a "scuba tank."