Editing Caterpillar (section)

== 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.

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|author1=Kukal, O.|author2=B. Heinrich|author3=J. G. Duman|name-list-style=amp|year=1988|title=Behavioral thermoregulation in the freeze-tolerant arctic caterpillar, ''Gynaeophora groenlandica''|journal=J. Exp. Biol.|volume=138|pages=181–193|url=http://jeb.biologists.org/cgi/content/abstract/138/1/181|issue=1|doi=10.1242/jeb.138.1.181|bibcode=1988JExpB.138..181K |access-date=2010-06-26|archive-date=2008-07-25|archive-url=https://web.archive.org/web/20080725165534/http://jeb.biologists.org/cgi/content/abstract/138/1/181|url-status=live}}</ref> apart from physiological adaptations to remain in a dormant state.<ref>{{cite journal|author1=Bennett, V. A.|author2=Lee, R. E.|author3=Nauman, L. S.|author4=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|access-date=2010-06-26|archive-date=2012-04-06|archive-url=https://web.archive.org/web/20120406084702/http://www.units.muohio.edu/cryolab/publications/documents/BennettLeeetal03.pdf|url-status=live}}</ref>

=== Appearance ===

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

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 or distasteful and their bright coloring [[Aposematism|warns predators of this]]. Others may [[Mimicry|mimic]] dangerous caterpillars or other animals while not being dangerous themselves. Many caterpillars are [[crypsis|cryptically]] colored and resemble the plants on which they feed. An example of caterpillars that use camouflage for defense is the species ''[[Nemoria arizonaria]]''. If the caterpillars hatch in the spring and feed on oak catkins they appear green. If they hatch in the summer they appear dark colored, like oak twigs. The differential development is linked to the tannin content in the diet.<ref>{{cite journal|last1=Greene|first1=E|year=1989|title=A Diet-Induced Developmental Polymorphism in a Caterpillar|journal=Science|volume=243|issue=4891|pages=643–646|bibcode=1989Sci...243..643G|doi=10.1126/science.243.4891.643|pmid=17834231|url=http://courses.biology.utah.edu/feener/5445/Readings/Lecture%2018/Greene%201989.pdf|citeseerx=10.1.1.462.1931|s2cid=23249256|access-date=2017-10-27|archive-date=2017-08-10|archive-url=https://web.archive.org/web/20170810102937/http://courses.biology.utah.edu/feener/5445/Readings/Lecture%2018/Greene%201989.pdf|url-status=live}}</ref> Caterpillars may even have spines or growths that resemble plant parts such as thorns. Some look like objects in the environment such as bird droppings. Some [[Geometridae]] cover themselves in plant parts, while [[bagworm]]s construct and live in a bag covered in sand, pebbles or plant material.

=== Chemical defenses ===

More aggressive self-defense measures have evolved in 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. Other caterpillars acquire toxins from their host plants that render them unpalatable to most of their predators. For instance, [[Utetheisa ornatrix|ornate moth]] caterpillars utilize [[pyrrolizidine alkaloids]] that they obtain from their food plants to deter predators.<ref>{{cite journal | last1 = Dussourd | first1 = D. E. | year = 1988 | title = Biparental Defensive Endowment of Eggs with Acquired Plant Alkaloid in the Moth ''Utetheisa ornatrix'' | journal = Proceedings of the National Academy of Sciences | volume = 85 | issue = 16| pages = 5992–996 | doi = 10.1073/pnas.85.16.5992 | pmid = 3413071 | pmc = 281891 | bibcode = 1988PNAS...85.5992D | doi-access = free }}</ref> 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 American [[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|author1=Malaque, Ceila M. S. |author2=Lúcia Andrade |author3=Geraldine Madalosso |author4=Sandra Tomy |author5=Flávio L. Tavares |author6=Antonio C. Seguro|year=2006|title= A case of hemolysis resulting from contact with a ''Lonomia'' caterpillar in southern Brazil|journal= American Journal of Tropical Medicine and Hygiene |volume=74|issue=5|pages= 807–809|pmid=16687684|doi=10.4269/ajtmh.2006.74.807|doi-access=free}}</ref> This chemical is being investigated for potential medical applications. Most urticating hairs range in effect from mild irritation to [[dermatitis]]. Example: [[brown-tail moth]].

[[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 ===
[[File:Chenilles_processionnaires_(14).JPG|thumb|Caterpillars linked together into a "procession"]]
Many caterpillars display feeding behaviors which allow the caterpillar to remain hidden from potential predators. Many feed in protected environments, such as enclosed inside silk galleries, rolled leaves or by [[leaf miner|mining]] between the leaf surfaces.

Some caterpillars, like early instars of the [[tomato hornworm]] and [[tobacco hornworm]], have long "whip-like" organs attached to the ends of their body. The caterpillar wiggles these organs to frighten away flies and predatory wasps.<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 journal | last1 = Bura | first1 = V. L. | last2 = Rohwer | first2 = V. G. | last3 = Martin | first3 = P. R. | last4 = Yack | first4 = J. E. | title = Whistling in caterpillars (Amorpha juglandis, Bombycoidea): Sound-producing mechanism and function | doi = 10.1242/jeb.046805 | journal = Journal of Experimental Biology | volume = 214 | issue = Pt 1 | pages = 30–37 | year = 2010 | pmid = 21147966| doi-access =  }}</ref>

=== Social behaviors and relationships with 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>[https://australian.museum/learn/animals/insects/lycaenid-butterflies-and-ants/ Lycaenid butterflies and ants] {{Webarchive|url=https://web.archive.org/web/20200731121813/https://australian.museum/learn/animals/insects/lycaenid-butterflies-and-ants/ |date=2020-07-31 }}. 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|author1=Entry, Grant L. G. |author2=Lee A. Dyer.|s2cid=14389136|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. [[Pine processionary]] (''Thaumetopoea pityocampa'') caterpillars often link into a long train to move through trees and over the ground. The head of the lead caterpillar is visible, but the other heads can appear hidden.<ref name="fitzgerald">{{cite web|url=http://web.cortland.edu/fitzgerald/PineProcessionary.html|title=Pine Processionary Caterpillar|author=Terrence Fitzgerald|publisher=Web.cortland.edu|access-date=2013-05-08|archive-date=2013-03-03|archive-url=https://web.archive.org/web/20130303191259/http://web.cortland.edu/fitzgerald/pineprocessionary.html|url-status=live}}</ref> [[Forest tent caterpillar moth|Forest tent caterpillars]] cluster during periods of cold weather.

=== Predators ===

Caterpillars are eaten by many animals. The [[European pied flycatcher]] is one species that preys upon caterpillars. The flycatcher typically finds caterpillars among oak foliage. [[Paper wasp]]s catch caterpillars to feed their young and themselves.