A compound eye is a visual organ found in arthropods such as insects and crustaceans . It may consist of thousands of ommatidia , which are tiny independent photoreception units that consist of a cornea , lens , and photoreceptor cells which distinguish brightness and color. The image perceived by this arthropod eye is a combination of inputs from the numerous ommatidia, which are oriented to point in slightly different directions. Compared with single-aperture eyes , compound eyes have poor image resolution ; however, they possess a very large view angle and the ability to detect fast movement and, in some cases, the polarization of light. Because a compound eye is made up of a collection of ommatidia, each with its own lens, light will enter each ommatidium instead of using a single entrance point. The individual light receptors behind each lens are then turned on and off due to a series of changes in the light intensity during movement or when an object is moving, creating a flicker-effect known as the flicker frequency, which is the rate at which the ommatidia are turned on and off– this facilitates faster reaction to movement; honey bees respond in 0.01s compared with 0.05s for humans.
20-557: Iliana is a genus of skippers in the family Hesperiidae . It was first described in 1937 by Ernest Layton Bell, with Iliana romulus as the type species. Species of the genus have a neotropical distribution. Species mainly occur in Peru, Brazil and Bolivia, with one species, Iliana remus , additionally known from French Guiana . The placement of Iliana within the Hesperiidae is not fully resolved. It has traditionally been placed within
40-425: A crochet hook , while the typical butterflies have club-like tips to their antennae, and moth-butterflies have feathered or pectinate (comb-shaped) antennae similar to moths . Skippers also have generally stockier bodies and larger compound eyes than the other two groups, with stronger wing muscles in the plump thorax , in this resembling many moths more than the other two butterfly lineages do. Unlike, for example,
60-420: A 2016 revision by Olaf Hermann Hendrik Mielke and Mirna Martins Casagrande, several changes to the genus were made: Eurypterus peruvianus and Tosta sapasoa were transferred to Iliana ; Tosta capra and Tosta saltarana were synonymized to Iliana romulus ; I. purpurascens and I. heros were transferred out of the genus; and three new species of Iliana were described. As of Mielke & Casagrande 2016,
80-751: A blackish streak or patch of scent scales on their forewings. Many species of skippers look very alike. For example, some species in the genera Amblyscirtes , Erynnis (duskywings), and Hesperia (branded skippers) cannot currently be distinguished in the field even by experts. The only reliable method of telling them apart involves dissection and microscopic examination of the genitalia , which have characteristic structures that prevent mating except between conspecifics . The roughly 3500 species of skippers are now classified in these subfamilies: Compound eye Compound eyes are typically classified as either apposition eyes, which form multiple inverted images, or superposition eyes, which form
100-456: A separate superfamily, Hesperioidea ; however, the most recent taxonomy places the family in the superfamily Papilionoidea , the butterflies. They are named for their quick, darting flight habits. Most have their antenna tips modified into narrow, hook-like projections. Moreover, skippers mostly have an absence of wing-coupling structure available in most moths. More than 3500 species of skippers are recognized, and they occur worldwide, but with
120-483: A single erect image. Apposition eyes can be divided into two groups. The typical apposition eye has a lens focusing light from one direction on the rhabdom , while light from other directions is absorbed by the dark wall of the ommatidium . The mantis shrimp is the most advanced example of an animal with this type of eye. In the other kind of apposition eye, found in the Strepsiptera , each lens forms an image, and
140-454: A transparent gap but use corner mirrors instead of lenses. Good fliers like flies or honey bees, or prey-catching insects like praying mantises or dragonflies , have specialized zones of ommatidia organized into a fovea area which gives acute vision. In the acute zone the eye is flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. There are some exceptions from
160-408: A way that resembles a true compound eye. Asymmetries in compound eyes may be associated with asymmetries in behaviour. For example, Temnothorax albipennis ant scouts show behavioural lateralization when exploring unknown nest sites, showing a population-level bias to prefer left turns. One possible reason for this is that its environment is partly maze-like and consistently turning in one direction
180-491: Is a good way to search and exit mazes without getting lost. This turning bias is correlated with slight asymmetries in the ants' compound eyes (differential ommatidia count). The body of Ophiomastix wendtii , a type of brittle star , was previously thought to be covered with ommatidia, turning its whole skin into a compound eye, but this has since been found to be erroneous; the system does not rely on lenses or image formation. "Dragonfly eyes" (Chinese: 蜻蜓眼 qingting yan ]
200-470: Is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialized retina. The resulting eye is a mixture of a simple eye within a compound eye. Another version is the pseudofaceted eye, as seen in Scutigera . This type of eye consists of a cluster of numerous ocelli on each side of the head, organized in
220-508: The Arctiinae , though, their wings are usually small in proportion to their bodies. Some have larger wings, but only rarely as large in proportion to the body as in other butterflies. When at rest, skippers keep their wings usually angled upwards or spread out, and only rarely fold them up completely. The wings are usually well-rounded with more or less sharply tipped forewings. Some have prominent hindwing tails, and others have more angled wings;
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#1732854810493240-453: The Neotropics, but recent phylogenetic analyses suggest the traditional Papilionoidea are paraphyletic , thus the subfamilies should be reorganised to reflect true cladistic relationships. Collectively, these three groups of butterflies share many characteristics, especially in the egg , larval , and pupal stages. Nevertheless, skippers have the antennae clubs hooked backward like
260-506: The Pyrgini, but Warren et al. (2008, 2009) place it in Carcharodini , which has been followed by many but not all subsequent publications including the genus. Mielke and Casagrande (2016) argue for its placement to remain in tribe Pyrgini until more in-depth reclassification has taken place. At the time the genus was erected, it contained two species, Iliana remus and Iliana romulus , with
280-425: The genus contains the following species: In Bell, Ernest Layton (1937). "New genera and species of Neotropical Hesperiidae with notes on others (Lepidoptera, Rhopalocera)" (PDF) . American Museum Novitates (914): 8–10. Skipper (butterfly) Skippers are a group of butterflies placed in the family Hesperiidae within the order Lepidoptera (moths and butterflies). They were previously placed in
300-496: The greatest diversity in the Neotropical regions of Central and South America. Traditionally, the Hesperiidae were placed in a monotypic superfamily Hesperioidea, because they are morphologically distinct from other Rhopalocera (butterflies), which mostly belong to the typical butterfly superfamily Papilionoidea . The third and rather small butterfly superfamily is the moth-butterflies (Hedyloidea), which are restricted to
320-470: The images are combined in the brain. This is called the schizochroal compound eye or the neural superposition eye (which, despite its name, is a form of the apposition eye). The superposition eye is divided into three subtypes; the refracting , the reflecting , and the parabolic superposition eye. The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to
340-533: The latter assigned as type species. Both species were at the time newly described by Bell from specimens from the collection of Hesperiidae held by the National Museum of Natural History . The specimens were originally collected at the Putumayo river in Peru. In 1953, Evans transferred Telemiades purpurascens and Echelatus heros to Iliana , and described a new subspecies of the latter, Iliana heros heroica . In
360-512: The same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This kind is used mostly by nocturnal insects. In the parabolic superposition eye , seen in arthropods such as mayflies , the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array . Long-bodied decapod crustaceans such as shrimp , prawns , crayfish and lobsters are alone in having reflecting superposition eyes , which also have
380-469: The skippers' basic wing shapes vary not much by comparison to the Papilionoidea, though. Most have a fairly drab coloration of browns and greys; some are more boldly black-and-white. Yellow, red, and blue hues are less often found, but some largely brown species are quite richly colored, too. Green colors and metallic iridescence are generally absent. Sexual dichromatism is present in some; males may have
400-405: The types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp, Dioptromysis paucispinosa . The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there
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