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Caterpillar

Caterpillars are the larval form of members of the order Lepidoptera (the insect order comprising butterflies and moths). They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture. Many moth species are better known in their caterpillar stages because of the damage they cause to fruits and other agricultural produce.

The etymological origins of the word are from the early 16th century, from Middle English catirpel, catirpeller, probably an alteration of Old North French catepelose: cate, cat (from Latin cattus) + pelose, hairy (from Latin pil sus).[1]

Contents


Classification

A geometrid caterpillar or inchworm
A geometrid caterpillar or inchworm
Crochets on a caterpillar's prolegs.

The geometrids, also known as inchworms or loopers, are so named because of the way they move, appearing to measure the earth (the word geometrid means earth-measurer in Greek); the primary reason for this unusual locomotion is the elimination of nearly all the prolegs except the clasper on the terminal segment.

Caterpillars have soft bodies that can grow rapidly between moults. Only the head capsule is hardened. The mandibles are tough and sharp for chewing leaves (this contrasts with most adult Lepidoptera, which have highly reduced or soft mandibles). Behind the mandibles of the caterpillar are the spinnerets, for manipulating silk.

Some larvae of the Hymenoptera order (ants, bees and wasps) can appear like the caterpillars of the lepidoptera. Such larvae are mainly seen in the sawfly family. However while these larvae superficially resemble caterpillars, they can be distinguished by the presence of prolegs on every abdominal segment, an absence of crochets or hooks on the prolegs (these are present on lepidopteran caterpillars), prominent ocelli on the head capsule, and an absence of the upside-down Y-shaped suture on the front of the head.[2]

Defenses

aposematic colouring]]. Many animals feed on caterpillars as they are rich in protein. As a result caterpillars have evolved various means of defense. The appearance of a caterpillar can often repel a predator: its markings and certain body parts can make it seem poisonous, or bigger in size and thus threatening, or non-edible. Some types of caterpillars are indeed poisonous, and are capable of shooting acid.

Some caterpillars have long "whip-like" organs attached to the ends of their body. The caterpillar wiggles these organs to frighten away flies.[3]

Caterpillars have evolved defenses against physical conditions such as cold, hot or dry environmental conditions. Some Arctic species like Gynaephora groenlandica have special basking and aggregation behaviours[4] apart from physiological adaptations to remain in a dormant state.[5]

Appearance

Costa Rican hairy caterpillar. The spiny bristles are a self-defense mechanism Many caterpillars are cryptically coloured and resemble the plants on which they feed and may even have parts that mimic plant parts such as thorns. Their size varies from as little as 1 mm to about . Some look like objects in the environment such as bird droppings. Many feed enclosed inside silk galleries, rolled leaves or by mining between the leaf surfaces. Caterpillars of Nemoria arizonaria that grow in spring feed on oak catkins and appear green. The summer brood appear like oak twigs. The differential development is linked to the tannin content in the diet.[6]

More aggressive self-defense measures are taken by some caterpillars. These measures include having spiny bristles or long fine hair-like setae with detachable tips that will irritate by lodging in the skin or mucous membranes.[2] However some birds (such as cuckoos) will swallow even the hairiest of caterpillars. The most aggressive caterpillar defenses are bristles associated with venom glands. These bristles are called urticating hairs. A venom which is among the most potent defensive chemicals in any animal is produced by the South American silk moth genus Lonomia. Its venom is an anticoagulant powerful enough to cause a human to hemorrhage to death (See Lonomiasis).[7] This chemical is being investigated for potential medical applications. Most urticating hairs range in effect from mild irritation to dermatitis.

Giant swallowtail caterpillar everting its osmeterium in defense Plants contain toxins which protect them from herbivores, but some caterpillars have evolved countermeasures which enable them to eat the leaves of such toxic plants. In addition to being unaffected by the poison, the caterpillars sequester it in their body, making them highly toxic to predators. The chemicals are also carried on into the adult stages. These toxic species, such as the Cinnabar moth (Tyria jacobaeae) and monarch (Danaus plexippus) caterpillars, usually advertise themselves with the danger colors of red, yellow and black, often in bright stripes (see aposematism). Any predator that attempts to eat a caterpillar with an aggressive defense mechanism will learn and avoid future attempts.

Larvae of Craesus septentrionalis, a sawfly showing 6 pairs of pro-legs.
Larvae of Craesus septentrionalis, a sawfly showing 6 pairs of pro-legs.
Some caterpillars regurgitate acidic digestive juices at attacking enemies. Many papilionid larvae produce bad smells from extrudable glands called osmeteria.

Caterpillars can evade predators by using a silk line and dropping off from branches when disturbed.

Some caterpillars obtain protection by associating themselves with ants. The Lycaenid butterflies are particularly well known for this. They communicate with their ant protectors by vibrations as well as chemical means and typically provide food rewards.[8]

Some caterpillars are gregarious; large aggregations are believed to help in reducing the levels of parasitization and predation.[9] Clusters amplify the signal of aposematic coloration, and individuals may participate in group regurgitation or displays.

Caterpillars can be confused with the larvae of sawflies (see image on right). Lepidopteran larvae can be differentiated by:

  • the numbers of pairs of pro-legs; sawfly larvae have 6 while caterpillars have up to 5 pairs.
  • the number of stemmata (simple eyes); the sawfly larvae have only two, while a caterpillar has six.
  • the presence of crochets on the prolegs; these are absent in the Symphyta (sawflies).

Behavior

A Pasture Day Moth caterpillar feeding on capeweed Caterpillars have been called "eating machines", and eat leaves voraciously. Most species shed their skin four or five times as their bodies grow, and they eventually pupate into an adult form.[10] Caterpillars grow very quickly; for instance, a tobacco hornworm will increase its weight ten-thousandfold in less than twenty days. An adaptation that enables them to eat so much is a mechanism in a specialized midgut that quickly transports ions to the lumen (midgut cavity), to keep the potassium level higher in the midgut cavity than in the blood.[11]

A Gypsy Moth caterpillar Most caterpillars are solely herbivorous. Many are restricted to one species of plant, while others are polyphagous. A few, including the clothes moth, feed on detritus. Most predatory caterpillars feed on eggs of other insects, aphids, scale insects, or ant larvae. Some are cannibals, and others prey on caterpillars of other species (e.g. Hawai'ian Eupithecia ). A few are parasitic on cicadas or leaf hoppers.[12] Some Hawai'ian caterpillars (Hyposmocoma molluscivora) use silk traps to capture snails.[13]

Many caterpillars are nocturnal. For example, the "cutworms" (of the Noctuidae family) hide at the base of plants during the day and only feed at night.[14] Others, such as gypsy moth (Lymantria dispar) larvae, change their activity patterns depending on density and larval stage, with more diurnal feeding in early instars and high densities.[15]

Economic effects

Hypsipyla grandela damages mahogany in Brazil

Caterpillars cause much damage, mainly by eating leaves. The propensity for damage is enhanced by monocultural farming practices, especially where the caterpillar is specifically adapted to the host plant under cultivation. The cotton bollworm causes enormous losses. Other species eat food crops. Caterpillars have been the target of pest control through the use of pesticides, biological control and agronomic practices. Many species have become resistant to pesticides. Bacterial toxins such as those from Bacillus thuringiensis which are evolved to affect the gut of Lepidoptera have been used in sprays of bacterial spores, toxin extracts and also by incorporating genes to produce them within the host plants. These approaches are defeated over time by the evolution of resistance mechanisms in the insects.[16]

Plants evolve mechanisms of resistance to being eaten by caterpillars, including the evolution of chemical toxins and physical barriers such as hairs. Incorporating host plant resistance (HPR) through plant breeding is another approach used in reducing the impact of caterpillars on crop plants.[17]

Some caterpillars are used in industry. The silk industry is based on the silkworm caterpillar.

Human health

Buck Moth caterpillar sting on a shin twenty-four hours after occurrence in south Louisiana. The reddish mark covers an area about 20 mm at its widest point by about 70 mm in length.

Caterpillar hair can be a cause of human health problems. Caterpillar hairs sometimes have venoms in them and species from approximately 12 families of moths or butterflies worldwide can inflict serious human injuries ranging from urticarial dermatitis and atopic asthma to osteochondritis, consumption coagulopathy, renal failure, and intracerebral hemorrhage.[18] Skin rashes are the most common, but there have been fatalities.[19] Lonomia is a frequent cause of envenomation in Brazil, with 354 cases reported between 1989 and 2005. Lethality ranging up to 20% with death caused most often by intracranial hemorrhage.[20]

Caterpillar hairs have also been known to cause kerato-conjunctivitis. The sharp barbs on the end of caterpillar hairs can get lodged in soft tissues and mucus membranes such as the eyes. Once they enter such tissues, they can be difficult to extract, often exacerbating the problem as they migrate across the membrane.[21]

This becomes a particular problem in an indoor setting. The hairs easily enter buildings through ventilation systems and accumulate in indoor environments because of their small size, which makes it difficult for them to be vented out. This accumulation increases the risk of human contact in indoor environments.[22]

Research

Earthwatch Institute is a global non-profit that teams volunteers with scientists to conduct important environmental research. They have multiple research programs called "Climate Change and Caterpillars" geared to understanding how they protect themselves and respond to changes in their habitats. Research expeditions are located in Quito, Ecuador,[23] Tucson, Arizona[24] and San Jose, Costa Rica.[25] In each expedition, volunteers conduct research such as finding and collecting caterpillars and their host plants, and helping to raise caterpillars at all stages of their life cycles and record their relationships with plants and parasites.

See also

  • Caterpillar dermatitis
  • Edible caterpillars
  • Larval food plants of Lepidoptera
  • Pests and diseases of roses
  • Larva

References

A Monarch butterfly (Danaus plexippus) caterpillar feeding on a leaf of the Swamp Milkweed (Asclepias incarnata) in a private garden in Lancaster, Pennsylvania.
A Monarch butterfly (Danaus plexippus) caterpillar feeding on a leaf of the Swamp Milkweed (Asclepias incarnata) in a private garden in Lancaster, Pennsylvania.
Dryas iulia
Dryas iulia
Caterpillar of Great Orange Tip resembling the Common green vine snake Ahaetulla nasuta.
Caterpillar of Great Orange Tip resembling the Common green vine snake Ahaetulla nasuta.

Gallery

Image:CH Caterpillar.jpg|Caterpillar of the Spurge Hawk-moth, near Binn, Valais, Switzerland at ca. 2 km altitude. Image:Caterpillar at 5th stage.jpg|Caterpillar of the Emperor Gum Moth. Image:Poplar hawk-moth.jpg|A poplar hawk-moth caterpillar (a common species of caterpillar in the UK). Image:Lycaenid_ant_sec.jpg|Ant tending a lycaenid caterpillar. Image:Snodgrass Schizura concinna.jpg|Life cycle of the red-humped caterpillar (Schizura concinna ). Image:Forest-tent-caterpillar-malacosoma-disstria.jpg|Forest tent caterpillar (Malacosoma disstria) Image:Eighteyescatterpilar.jpg| Camouflage: apparently with eight eyes, only two of them are real. Photo in a eucalyptus tree, Sao Paulo, Brazil Image:AntheraeaPolyphemusCaterpillar.jpg|Caterpillar of the Polyphemus moth (Antheraea polyphemus), Virginia, USA Image:Baby Caterpillars crop2.jpg|Caterpillars hatching on an apple tree in Victoria, BC, Canada Image:Hairy Caterpillar.jpg|Caterpillar in a tree, India

External links

ar: ay:Laqatu bjn:Hulat be: ca:Eruga cv: cs:Housenka de:Raupe (Schmetterling) et:R vik nv:Ch osh dit oo es:Oruga (larva) eo:Ra po eu:Beldar fa: fr:Chenille (l pidopt re) fy:R p gd:Burras gl:Eiruga hi: hr:Gusjenica io:Raupo id:Ulat it:Bruco he: jv:Uler ht:Chini ku:Ma ot lbe: lt:Vik ras ln:Momb nz hu:Herny ms:Beluncas my: nl:Rups ja: nrm:Carp leuse oc:Canilha (lepidopt r) pcd:Carplute pl:G sienica (larwa) pt:Lagarta ru: sco:Oobit scn:Campa simple:Caterpillar sk:H senica sl:Gosenica sr: su:Hileud sv:Fj rilslarv tl:Higad te: th: chr: tr:T rt l uk: vi:S u b m wa:Halene zh:






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