|Megalagrion is a genus of damselflies
in the family Coenagrionidae It contains approximately 26 species, all
of which are endemic to Hawaii. Larval Megalagrion live in widely diverse
habitats, including the expected streams and pools. Megalagrion also exploit
some surprising habitats such as plant leaf axils, waterfall faces, and
even damp fern litter far from water sources. M. oahuense is the only species
of damselfly whose naiad is terrestrial, living in damp fern litter until
metamorphosis. Many species of Megalagrion are in danger due to habitat
loss and predation by non-native fish.
Megalagrion leptodemas (Perkins,
1899) is endemic to the Hawaiian island of O'ahu, and is considered
one of the rarest and most vulnerable of all endemic Megalagrion species
in Hawaii. Megalagrion leptodemas was found historically in the mountain
ranges of Koolau and Waianae, and is currently restricted to scattered
sites in four drainages in the Koolau Range. Its limited habitat and small
scattered populations may affect long-term stability. The species is susceptible
to the effects of habitat loss and introduced species. Research should
focus on habitat management and protection, and control of invasive species.
It is one of the smaller Hawaiian
damselflies, about 36-41 mm in length with a wingspan of 39-42 mm. Males
are slender, with brilliant red coloration on the head, thorax, and abdomen,
and black markings on the top of abdominal segments five through seven.
Females are similar in color but have pale green to grayish-olive markings
on the body, and the top of their abdomen is mostly black.
Larvae of this species reach 200
mm in length. The three flattened, oval, leaf-like gills at the tip of
the abdomen have prominent branching veins, and are darker-colored at the
base and paler at the tips. The predaceous aquatic nymphs inhabit standing
pools in intermittent mid-elevation streams, and slow sections of perennial
upland streams. Adults are quick fliers but do not disperse far from the
nymphal habitat, patrolling short lengths of the stream and laying eggs
in the slow reaches of streams and in stream pools.
Recent surveys have indicated that
this species is confined to widely scattered subpopulations in four drainages
in the Koolau Mountains of Oahu. One of these catchments has been the site
of recent freeway construction. There probably are less than 1,000
individuals remaining at present. IUCN Red List accessed as Critically