True water beetle

The Dytiscidae are the predaceous diving beetles, a family of water beetles. They are about 25 mm (1.0 in) long on average, though much variation is seen between species. Dytiscus latissimus, the largest, can grow to 45 mm long. Most are dark brown, blackish, or dark olive in color with golden highlights in some subfamilies. They have short, but sharp mandibles. Immediately upon biting, they deliver digestive enzymes. The larvae are commonly known as water tigers. For more information, visit the Wikipedia entry. Get back to Coleoptera
Cybister japonicus