Thenus

Lore & Background

Thenus orientalis has a strongly depressed body and grows to a maximum body length of 25 cm, or a carapace length of 8 cm. Its eyes are placed at the margin of the carapace, a feature that distinguishes it from the similar Balmain bug (Ibacus peronii), whose eyes are near the midline. The species is known by several common names: the United Nations Food and Agriculture Organization prefers flathead lobster, while in Australia it is widely called the Moreton Bay bug, often shortened to just bug, after Moreton Bay in Brisbane, Queensland. In Singapore, both the flathead lobster and true crayfish are called crayfish, and they are used in many Singaporean dishes.

Reader's Guide

Thenus orientalis holds significance as a harvested species across its Indo-West Pacific range, from the east coast of Africa to China, southern Japan, the Philippines, and along the northern coast of Australia from Western Australia to Queensland. It is also caught on a small scale off the shores of Malaysia and Singapore. The species is a familiar item in seafood markets, as seen in Thailand, and its flesh is prepared prior to cooking. The confusion with the Balmain bug (Ibacus peronii) highlights the importance of the eye-placement distinction for accurate identification. The variety of common names—flathead lobster, Moreton Bay bug, and crayfish in Singapore—reflects its widespread use and regional culinary traditions. Its legacy lies in its role as a commercially fished lobster that supports local fisheries and appears in diverse cuisines, from Australian seafood dishes to Singaporean recipes.

Did You Know?

• Thenus orientalis is known as the Moreton Bay bug in Australia, named after Moreton Bay in Brisbane, Queensland.
• The eyes of Thenus orientalis are at the margin of the carapace, unlike the Balmain bug whose eyes are near the midline.
• Thenus orientalis has a maximum body length of 25 cm.