Respiration takes place through the thoracic spiracles with the caudal lamellae or gills acting as supplementary respiratory structures, unlike the rectum which is the primary respiratory structure in most Odonata.
Odonates have highly developed sight. The large compound eyes are used to capture prey.
Communication Channels: chemical
Perception Channels: visual ; infrared/heat ; tactile ; chemical
This damselfly is not listed as endangered or threatened, but is considered rare in its range.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: vulnerable
Odonate eggs hatch in 12-30 days, depending on temperature and moisture. Metamorphosis is incomplete and odonate nymphs usually go through 10-15 instars.
This species also has no negative economic benefits to humans.
The San Francisco fork-tailed damselfly has no positive economic benefits to humans.
Adults and nymphs of Odonata eat many pest insect species, such as mosquitoes. The nymphs play an important role as food for fish.
Ischnura gemina are carnivorous insects that prey on mosquitoes, annelids, small crustaceans, and mollusks. They usually catch their food on their wing after stalking the prey by remaining motionless until the food comes within reach and is seized by rapid extension and contraction of the labium. The labium then holds the food in their mouth where it is crushed easily by the strong mandibles.
Animal Foods: insects; mollusks; aquatic or marine worms; aquatic crustaceans
Primary Diet: carnivore (Insectivore , Eats non-insect arthropods, Molluscivore , Vermivore)
This nonmigratory species is restricted to the San Francisco Bay area in California.
Biogeographic Regions: nearctic (Native )
Ischnura gemina are active on sunny, warm days near any water body, such as a lake, river, pond, hotsprings (up to 120 degrees F), cold glacial streams, swift rapids, or very salty lakes. They are very rare in polluted water. The eggs and larvae are aquatic and nymphs are found on submerged vegetation and on the bottom of these bodies of water. Climber nymphs are usually found on debris in the water and move about at a slow pace in dense vegetation.
Habitat Regions: freshwater
Aquatic Biomes: lakes and ponds; rivers and streams; coastal ; brackish water
The cycle from egg to adult takes about one year. Females usually survive longer than males.
Ischnura gemina are known for their large compound eyes each separated by more than their own body width, muscular mandibles, very slender, elongate ten-segmented abdomens, short legs used mostly for perching, and tiny filiform antennae. Sight is their most specialized sense. Unlike the dragonfly, their two pairs of large wings stand straight up over their 7-8 cm long bodies. The female adult has a black humeral stripe, lacking the pale spot located at the base of the median ocellus that the males exhibit. Females also have specialized ovipositors whose primary function is to cut holes in the stems of submerged plants in order to receive eggs. Adults are called "darning needles" or "mosquito hawks" due to their size, which decreases with advancing season.
Each adult female usually has 11 to 14 nymphs, whose life cycles take up to one year. The eggs and larvae have caudal and rectal gills. Ischnura gemina nymphs are identified by their three leaflike tracheal gills at the tip of their abdomen and their usually robust green or grey color. Nymphs are usually 10-15 mm long, not including their gills. The bodies of the nymphs bear small spines and are often covered with algae and debris. They have five labial setae or food getting devices armed with stout teeth.
Range length: 7 to 8 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes colored or patterned differently
Predators of I. gemina include falcons, herons, gulls, sandpipers, grackles, red-winged blackbirds, bats, spiders, and wasps. Weather is responsible for considerable mortality. For example, cloudy, rainy days and windstorms drive damselflies out to sea or into large lakes. Females usually survive longer than males.
Known Predators:
Flight time occurs from May to November. Mating is a very specialized and time-dependent process and occurs at rest or during flight. Females mate only once per clutch laid. Each adult female usually has 11 to 14 nymphs. The male is nonterritorial, the oviposition site rendezvous is widely dispersed and there can be multiple matings per day. In studies, females mated a second time with the same male in only 7.6% of cases and a third time only 0.9% of the time. Three percent of males and 5% of females had the same distributions for mating frequency. The sex ratio in studies was 50%. Mating and reproduction were directly related to the number of sunny days in which the male was sexually active.
When mating, the male grips the female around her neck with two of his pairs of claspers at the end of his abdomen. The female then arches her abdomen forward and under to come into contact with the sperm. Sperm is stored in the male's accessory genitalia on the underside of his thorax. Ischnura gemina oviposits in tandem, which is unusual in that the male possesses a "scoop" on his penis. This scoop's sole purpose is probably to displace the sperm. Post-copulatory guarding prevents sperm from being displaced by a rival mate. When the time has come to deposit the eggs, the female inserts them in plant tissue above or below water, sometimes in masses of green algae. The pre-reproductive period is 5-7 days.
Key Reproductive Features: seasonal breeding ; sexual ; fertilization (Internal ); oviparous
Ischnura gemina is a species of damselfly in the family Coenagrionidae known by the common name San Francisco forktail. It is endemic to the San Francisco Bay Area in California in the United States. This uncommon insect has a total range of less than 500 square miles in the Bay Area, occurring only in greater San Francisco and parts of San Mateo and Marin Counties.[2] This species is "one of the rarest Odonates in the United States."[1]
This damselfly is about 2.5 centimeters long. The male is mostly black with blue sides on the thorax and blue dots toward the tip of the abdomen. The female has dull green coloration on the sides of the thorax.[2] This species is similar to Ischnura denticollis, and can be distinguished by the shape of the male genital appendages. The two species are thought to hybridize.[2]
This damselfly is active between March and November, and adults are known to live over 30 days, a relatively long adult life for damselflies. This species occurs in coastal regions of the Bay Area; it is thought that its long life and long flight season are adaptations to the foggy climate of the region.[3]
The natural habitat of the species is the various wetland ecosystems of the San Francisco Bay Area, including seepages and ponds. It can tolerate some disturbance, such as channelization of waterways, as long as there is marshy vegetation cover. The larvae develop in the cover of aquatic plants and the adults feed on other wetland arthropods.[2]
Populations of this damselfly have been extirpated due to the destruction and degradation of habitat in the heavily urbanized area where it occurs. It lived in wetland habitat in Glen Canyon Park in the city of San Francisco until these moist spots were fragmented too extensively to support populations. After patches of wetland in the park were restored, the damselfly was reintroduced and persisted for a short while before disappearing once more. Though the reintroduction failed, it provided data about the habitat requirements for the insect.[4]
This had been designated an endangered species on the IUCN Red List because of its very small range, small populations within that range, and extensive destruction of its habitat. It has been downgraded to vulnerable status because it has been located at a few more sites, it has good dispersal ability, and it is relatively resistant to some of the forms of habitat degradation that it faces, such as pollution.[1]
Ischnura gemina is a species of damselfly in the family Coenagrionidae known by the common name San Francisco forktail. It is endemic to the San Francisco Bay Area in California in the United States. This uncommon insect has a total range of less than 500 square miles in the Bay Area, occurring only in greater San Francisco and parts of San Mateo and Marin Counties. This species is "one of the rarest Odonates in the United States."
