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NATURAL HISTORY

OCEANIC HAWAIIAN DAMSELFLY } Megalagrion oceanicum
FAMILY: Coenagrionidae

DESCRIPTION: The oceanic Hawaiian damselfly has beautiful, translucent wings and a black body interspersed with red or green depending on its gender.

HABITAT: The damselfly is found in fresh, running water in streams and marshes. Immature damselflies of this species are found amid gravel and moss pads in the swift-water sections of perennial streams.

RANGE: The species lives on the windward side of the Koolau Mountains, on the island of Oahu, Hawaii. It has been extirpated from the Waianae mountain range.

MIGRATION: The oceanic Hawaiian damselfly is nonmigratory.

BREEDING: During copulation, and often while the female lays eggs, the male damselfly grasps the female behind the head with his terminal abdominal appendages to guard her against rival males. The females lay eggs in submerged aquatic vegetation or in mats of moss or algae on submerged rocks.

LIFE CYCLE: Eggs hatch in about 10 days; the immature damselflies, called naiads, are aquatic. Naiads may take up to four months to mature, after which they crawl out of the water onto rocks or vegetation and molt into winged adults. Adults typically remain very close to the aquatic habitat from which they emerged.

FEEDING: Naiads are predacious, feeding on small aquatic invertebrates or fish. Adults are also predatory and feed on small flying insects such as midges.

THREATS: Damselflies are hurt by severe alteration and degradation of streams and marsh habitat on Oahu through agricultural water diversions and urban development, introduction of nonnative insects and fish that prey on damselflies, and alteration of habitat by invasive plants.

POPULATION TREND: Historically known from at least 16 localities on Oahu, by 2001 there were just seven oceanic Hawaiian damselfly populations remaining and a total population of fewer than 1,000 damselflies.

Photo © David Preston and Don Polhemusi