Thermonectus is a genus of beetles in the family Dytiscidae. This genus is native to the New World, and mainly from warm temperate to tropical in distribution, but one species, T. basillaris occurs as far north as southern Ontario, Canada. They inhabit a wide range of freshwater habitats with static water and are often common. They are generally about 0.8–1.5 cm (0.3–0.6 in) long and a few species from desert pools in North America have a distinct yellow-spotted pattern on a black background.

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