The Twilit Bloat is a mini-boss appearing in Twilight Princess. This creature is a bloated, giant Shadow Insect with tentacles emerging from its abdomen that can release electric shockwaves. This larger variant has the unique ability to swim underwater. Judging by its size and status as a mini-boss, it is plausible that this variant is the Queen of the Shadow Insects, as queen insects are characteristically larger to enable reproduction.
To defeat Twilit Bloat, Link must wait until it isn't charging him or is bursting with electricity. He must then L-target it and leap onto its lower section, then proceeding to hold the L button and repeatedly press A to bite it furiously. The young hero must repeat these steps a few more times and it will eventually fall into the water, lying on its back. At this point, Link must jump on its belly and use the energy field with Midna's help to attack its six tentacles at the same time. Once they are all destroyed in the same instant, it will shrivel up and die. This will release the last tear of light Link will collect, allowing him to finish returning light to Hyrule.
The Twilit Bloat when it's first seen
Link attacking the Bloat's chest
The Twilit Bloat highly resembles a type of real-life sea crustacean known as a giant isopod.
↑"Twilit Bloat ... Disturbing as it may seem, you have to defeat this bloated creature with bite attacks. It will be a true measure of your heroism. And it's the only way to fill the Vessel of Light to restore the spirits! Encountered In: Lanayru Province" (The Legend of Zelda: Twilight Princess Premium Edition strategy guide (Prima Games), pg. 22)