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'''Caterpillars''' are the [[larva]]l form of members of the [[order (biology)|order]] [[Lepidoptera]] (the [[insect]] order comprising [[butterfly|butterflies]] and [[moth]]s). They are mostly [[herbivore|herbivorous]] in food habit, although some species are [[insectivore|insectivorous]]. Caterpillars are voracious feeders and many of them are considered to be [[Pest (organism)|pest]]s 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 French|Old North French]] ''catepelose'': ''cate'', cat (from Latin ''cattus'') + ''pelose'', hairy (from Latin ''pilōsus'').<ref>[http://dictionary.reference.com/browse/caterpillar "Caterpillar"]. Dictionary.com. The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. (accessed: March 26, 2008).</ref>

==Classification==

[[Image:Geometridae.jpg|thumb|left|A [[Geometridae|geometrid]] caterpillar or inchworm]]

[[File:Crochets.jpg|thumb|Crochets on a caterpillar's prolegs.]]

[[Image:Craesus septentrionalis.jpg|thumb|Larvae of ''[[Nematinae|Craesus]] septentrionalis'', a [[sawfly]] showing 6 pairs of pro-legs.]]

The [[Geometridae|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 language|Greek]]); the primary reason for this unusual locomotion is the elimination of nearly all the [[proleg]]s except the clasper on the terminal segment.

Caterpillars have soft bodies that can grow rapidly between moults. Only the head capsule is hardened. The [[Mandible (insect mouthpart)|mandible]]s 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 [[spinneret (spider)|spinneret]]s, 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 (anatomical)|suture]] on the front of the head.<ref name="scoble">Scoble, MJ. 1995. [http://books.google.com/books?id=gnpd_5iNTiwC&printsec=frontcover The Lepidoptera: Form, function and diversity]. Oxford Univ. Press. ISBN 0-19-854952-0</ref>

Caterpillars can be confused with the larvae of [[Symphyta|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).

==Defenses==

[[File:Acharia stimulea 0795036.jpg|thumb|left|The [[saddleback caterpillar]] has [[urticating hair]] and [[aposematism|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.

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<ref>{{cite journal|author=Kukal, O., B. Heinrich, and J. G. Duman|year=1988|title=Behavioral thermoregulation in the freeze-tolerant arctic caterpillar, Gynaeophora groenlandica|journal=J. Exper. Biol.|volume=138|pages=181–193|url=http://jeb.biologists.org/cgi/content/abstract/138/1/181|issue=1}}</ref> apart from physiological adaptations to remain in a dormant state.<ref>{{cite journal|author=Bennett, V. A. Lee, R. E. Nauman, L. S. Kukal, O.|year=2003|title=Selection of overwintering microhabitats used by the arctic woollybear caterpillar, Gynaephora groenlandica|url=http://www.units.muohio.edu/cryolab/publications/documents/BennettLeeetal03.pdf|pmid=12908029|journal= Cryo Letters|volume= 24|issue=3|pages=191–200}}</ref>

===Appearance===

[[File:Hairy caterpillar (Costa Rica).jpg|thumb|[[Costa Rica]]n hairy caterpillar. The spiny bristles are a self-defense mechanism]]

Many caterpillars are [[crypsis|cryptically]] colored and resemble the plants on which they feed. They may even have parts that [[mimic]] plant parts such as thorns. Their size varies from as little as 1&nbsp;mm to about {{convert|75|mm|in}}. Some look like objects in the environment such as bird droppings. Many feed enclosed inside silk galleries, rolled leaves or by [[leaf miner|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.<ref>{{cite journal|doi=10.1126/science.243.4891.643|pmid=17834231|year=1989|last1=Greene|first1=E|title=A Diet-Induced Developmental Polymorphism in a Caterpillar|volume=243|issue=4891|pages=643–646|journal=Science}}</ref>

===Chemical defenses===

More aggressive self-defense measures are taken by some caterpillars. These measures include having spiny bristles or long fine hair-like [[seta]]e with detachable tips that will irritate by lodging in the skin or mucous membranes.<ref name="scoble"/> However some birds (such as [[cuckoo]]s) will swallow even the hairiest of caterpillars. The most aggressive caterpillar defenses are bristles associated with [[venom]] glands. These bristles are called [[urticating hair]]s. A venom which is among the most potent defensive chemicals in any animal is produced by the [[South America]]n [[Saturniidae|silk moth]] genus ''[[Lonomia]]''. Its venom is an [[anticoagulant]] powerful enough to cause a human to [[hemorrhage]] to death (See [[Lonomia]]sis).<ref>{{cite journal|author=Malaque, Ceila M. S., Lúcia Andrade, Geraldine Madalosso, Sandra Tomy, Flávio L. Tavares, And Antonio C. Seguro.|year=2006|title= A case of hemolysis resulting from contact with a ''Lonomia'' caterpillar in southern Brazil|url=http://www.ajtmh.org/cgi/content/full/74/5/807|journal= Am. J. Trop. Med. Hyg.|volume=74|issue=5|pages= 807–809|pmid=16687684}}</ref> This chemical is being investigated for potential medical applications. Most urticating hairs range in effect from mild irritation to [[dermatitis]].

[[File:Papilio cresphontes larva defensive.JPG|thumb|left|[[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 [[wikt:sequester|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.

Some caterpillars regurgitate acidic digestive juices at attacking enemies. Many [[Papilionidae|papilionid]] larvae produce bad smells from extrudable glands called [[osmeterium|osmeteria]].

===Defensive behaviors===

Some caterpillars have long "whip-like" organs attached to the ends of their body. The caterpillar wiggles these organs to frighten away flies.<ref>{{Cite book|last = Darby|first = Gene|title = What is a Butterfly|publisher = Benefic Press|location = Chicago|year = 1958|page = 13}}</ref> Some caterpillars can evade predators by using a silk line and dropping off from branches when disturbed. Many species thrash about violently when disturbed to scare away potential predators. One species ([[Amorpha juglandis]]) even makes high pitched whistles that can scare away birds.<ref>{{cite doi|10.1242/​jeb.046805}}</ref>

===Use of other insects===

Some caterpillars obtain protection by associating themselves with [[ant]]s. The [[Lycaenidae|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.<ref>[http://www.australianmuseum.net.au/Lycaenid-butterflies-and-ants Lycaenid butterflies and ants]. Australian museum (2009-10-14). Retrieved on 2012-08-14.</ref>

Some caterpillars are [[gregarious]]; large aggregations are believed to help in reducing the levels of parasitization and predation.<ref>{{cite journal|author=Entry, Grant L. G., Lee A. Dyer.|year=2002|title=On the Conditional Nature Of Neotropical Caterpillar Defenses against their Natural Enemies|jstor=3071846|journal= Ecology|volume=83|issue=11|pages=3108–3119|doi=10.1890/0012-9658(2002)083[3108:OTCNON]2.0.CO;2}}</ref> Clusters amplify the signal of aposematic coloration, and individuals may participate in group regurgitation or displays.

===Predators===

The caterpillar suffers predation from a number of species. The [[European pied flycatcher]] is one species that preys upon caterpillars. The flycatcher typically finds caterpillars amongst oak foliage.

==Behavior==

[[File:Pasture day moth caterpillar closeup.jpg|thumb|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 [[pupa]]te into an adult form.<ref>[http://www.scienceprojectlab.com/monarch-butterfly.html Monarch Butterfly]. Scienceprojectlab.com. Retrieved on 2012-08-14.</ref> 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.<ref>{{cite journal|author=Chamberlin, M.E. and M.E. King |journal= J. Exp. Zool. |volume=280|pages=135–141|doi=10.1002/(SICI)1097-010X(19980201)280:2<135::AID-JEZ4>3.0.CO;2-P|title=Changes in midgut active ion transport and metabolism during the fifth instar of the tobacco hornworm (Manduca sexta)|year=1998|issue=2}}</ref>

[[File:Gypsy moth caterpillar.JPG|thumb|left| A [[Gypsy Moth]] caterpillar]]

Most caterpillars are solely [[herbivore|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 predatory, and others prey on caterpillars of other species (e.g. Hawai'ian ''[[Eupithecia]]''). A few are parasitic on cicadas or leaf hoppers.<ref name="pierce">{{cite journal|author=Pierce, N.E.|year=1995|title=Predatory and parasitic Lepidoptera: Carnivores living on plants|journal=Journal of the Lepidopterist's Society|volume= 49|issue=4|pages= 412–453}}</ref> Some Hawai'ian caterpillars (''[[Hyposmocoma molluscivora]]'') use silk traps to capture snails.<ref>{{cite journal|author=Rubinoff, Daniel and William P. Haines|doi=10.1126/science.1110397|pmid=16040699|year=2005|last1=Rubinoff|first1=D|last2=Haines|first2=WP|title=Web-spinning caterpillar stalks snails|volume=309|issue=5734|page=575|journal=Science}}</ref>

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.<ref>{{cite web|publisher=USGS|url=http://www.npwrc.usgs.gov/resource/insects/catnw/ecol.htm|title=Caterpillars of Pacific Northwest Forests and Woodlands}}</ref> 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.<ref>{{cite journal|doi=10.1111/j.1365-2311.1987.tb01005.x|title=Behaviour of late-instar gypsy moth larvae in high and low density populations|year=1987|last1=Lance|first1=D. R.|journal=Ecological Entomology|volume=12|page=267|last2=Elkinton|first2=J. S.|last3=Schwalbe|first3=C. P.|issue=3}}</ref>

==Economic effects==

[[File:hypsipyla.jpg|thumb|''[[Hypsipyla grandela]]'' damages [[mahogany]] in [[Brazil]]]]

Caterpillars cause much damage, mainly by eating leaves. The propensity for damage is enhanced by [[monoculture|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 [[pesticide]]s, [[biological control]] and [[agronomy|agronomic]] practices. Many species have become resistant to [[pesticide]]s. 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.<ref>[http://www.dec.ny.gov/animals/7111.html Tent Caterpillars and Gypsy Moths]. Dec.ny.gov. Retrieved on 2012-08-14.</ref>

Plants evolve mechanisms of resistance to being eaten by caterpillars, including the evolution of chemical toxins and physical barriers such as hairs. Incorporating [[Plant defense against herbivory|host plant resistance]] (HPR) through plant breeding is another approach used in reducing the impact of caterpillars on crop plants.<ref>{{cite journal|url=http://www.ingentaconnect.com/content/esa/aesa/1999/00000092/00000006/art00002|title=Transgenic Host Plant Resistance to Insects—Some Reservations|author=van Emden, H. F.|journal=Annals of the Entomological Society of America|volume=92|issue=6|year=1999|pages=788–797}}</ref>

Some caterpillars are used in industry. The [[silk]] industry is based on the [[bombyx mori|silkworm]] caterpillar.

==Human health==

[[File:Sting0310.jpg|thumb|150px|left|[[Buck Moth]] caterpillar sting on a shin twenty-four hours after occurrence in south [[Louisiana]]. The reddish mark covers an area about 20&nbsp;mm at its widest point by about 70&nbsp;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 [[urticaria]]l dermatitis and [[atopic]] [[asthma]] to [[osteochondritis]], consumption [[coagulopathy]], [[renal]] failure, and [[brain|intracerebral]] [[hemorrhage]].<ref>{{cite journal|author=Diaz, HJ|year=2005|title=The evolving global epidemiology, syndromic classification, management, and prevention of caterpillar envenoming|pmid=15772333|journal=Am. J. Trop. Med. Hyg.|volume=72|pages=347–357|issue=3}}</ref> Skin rashes are the most common, but there have been fatalities.<ref>{{cite journal|author=J. Redd, R. Voorhees, T. Török |title=Outbreak of lepidopterism at a Boy Scout camp|journal= Journal of the American Academy of Dermatology|volume=56|issue=6|pages=952–955|doi=10.1016/j.jaad.2006.06.002|pmid=17368636|year=2007|last1=Redd|first1=JT|last2=Voorhees|first2=RE|last3=Török|first3=TJ}}</ref> ''[[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.<ref>{{cite journal|doi=10.1590/S0004-282X2006000600029|pmid=17221019|year=2006|month= December|last1=Kowacs|first1=PA|last2=Cardoso|first2=J|last3=Entres|first3=M|last4=Novak|first4=EM|last5=Werneck|first5=LC|title=Fatal intracerebral hemorrhage secondary to Lonomia obliqua caterpillar envenoming: case report|volume=64|issue=4|pages=1030–2|journal=Arquivos de neuro-psiquiatria|url=http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0004-282X2006000600029&lng=en&nrm=iso&tlng=en}}</ref>

Caterpillar hairs have also been known to cause [[keratin|kerato]]-[[conjunctivitis]]. The sharp barbs on the end of caterpillar hairs can get lodged in soft tissues and [[mucus membrane]]s 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.<ref>{{cite journal|author=Patel RJ, Shanbhag RM|title= Ophthalmia nodosa – (a case report)|url=http://www.ijo.in/article.asp?issn=0301-4738;year=1973;volume=21;issue=4;spage=208;epage=208;aulast=Patel|journal= Indian J Ophthalmol|year=1973|volume=21|page=208|issue=4}}</ref>

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.<ref>{{cite journal|author=Corrine R Balit, Helen C Ptolemy, Merilyn J Geary, Richard C Russell and Geoffrey K Isbister|pmid=11837874|year=2001|first1=CR|first2=HC|first3=MJ|first4=RC|first5=GK|title=Outbreak of caterpillar dermatitis caused by airborne hairs of the mistletoe browntail moth (Euproctis edwardsi)|volume=175|issue=11–12|pages=641–3|journal=The Medical journal of Australia|url=http://www.mja.com.au/public/issues/175_12_171201/balit/balit.html|issn=0025-729X}}</ref>

==Research==

{{Expand section|date=May 2012}}

[[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,<ref>{{cite web|url=http://www.earthwatch.org/exped/dyer_ecuador.html |title=Earthwatch: Climate Change and Caterpillars in Ecuador}}</ref> Tucson, Arizona<ref>{{cite web|url=http://www.earthwatch.org/exped/dyer_arizona.html |title=Earthwatch: Climate Change and Caterpillars in Arizona}}</ref> and San Jose, Costa Rica.<ref>{{cite web|url= http://www.earthwatch.org/europe/exped/dyer_costarica.html |title=Earthwatch: Climate Change and Caterpillars in Costa Rica}}</ref> 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.