Defense in insects

Examples of defenses that have withstood the test of time include hiding, escape by flight or running, and firmly holding ground to fight as well as producing chemicals and social structures that help prevent predation.

One of the best known modern examples of the role that evolution has played in insect defenses is the link between melanism and the peppered moth (Biston betularia).

[2] When an insect looks like an inedible or inconsequential object in the environment that is of no interest to a predator, such as leaves and twigs, it is said to display mimesis, a form of crypsis.

Additionally, camouflage is effective when it results in patterns or unique morphologies that disrupt outlines so as to better merge the individual into the background.

[3] Mimicry is a form of defense which describes when a species resembles another recognized by natural enemies, giving it protection against predators.

Automimics are individuals that, due to environmental conditions, lack the distasteful or harmful chemicals of conspecifics, but are still indirectly protected through their visibly identical relatives.

[2] An example can be found in the plain tiger (Danaus chrysippus), a non-edible butterfly, which is mimicked by multiple species, the most similar being the female danaid eggfly (Hypolimnas misippus).

Although its main role lies in support and muscle attachment, when extensively hardened by the cross-linking of proteins and chitin, or sclerotized, the cuticle acts as a first line of defense.

[2] This is the case in caddisfly larvae (order Trichoptera) which encase their abdomen with a mixture of materials like leaves, twigs, and stones.

They tend to have low molecular weight and are volatile and reactive, including acids, aldehydes, aromatic ketones, quinones, and terpenes.

[2] Pasteels, Grégoire, and Rowell-Rahier [9] grouped chemical defenses into three types: compounds that are truly poisonous, those that restrict movement, and those that repel predators.

Impairment of movement and sense organs is achieved through sticky, slimy, or entangling secretions that act mechanically rather than chemically.

[9] When startled, the assassin bug Platymeris rhadamanthus (family Reduviidae),[8] is capable of spitting venom up to 30 cm at potential threats.

The saliva of this insect contains at least six proteins including large amounts of protease, hyaluronidase, and phospholipase which are known to cause intense local pain, vasodilation, and edema.

[10] The majority of termite soldiers secrete a rubberlike and sticky chemical concoction that serves to entangle enemies, called a fontanellar gun,[10] and it is usually coupled with specialized mandibles.

[8] Among termite species in the Apicotermitinae that are soldierless or where soldiers are rare, mouth secretions are commonly replaced by abdominal dehiscence.

Within the subfamily Formicinae, the stinger has been lost and instead the poison gland forcibly ejects the fluid of choice, formic acid.

[15] Since leaf beetles produce high concentrations of 3-NPA esters, a powerful chemical defense against a wide range of different predators is obvious.

These droplets are immediately presented after mechanical disturbance and contain volatile compounds that derive from sequestered plant metabolites.

[19] The larvae of leaf beetles from the subfamilies of e.g., Criocerinae and Galerucinae often employ fecal shields, masses of feces that they carry on their bodies to repel predators.

More than just a physical barrier, the fecal shield contains excreted plant volatiles that can serve as potent predator deterrents.

The remaining larvae lie inside this defensive ring where the defenders repel predators through threatening attitudes, regurgitation, and biting.

[22] Termites (order Isoptera), like eusocial ants, wasps, and bees, rely on a caste system to protect their nests.

[23] The Trigona fuscipennis species in particular, make use of attraction, landing, buzzing and angular flights as typical alarm behaviors.

They can elicit both aggregational and dispersive responses in social insects depending on the alarm caller's location relative to the nest.

Firstly, the body-enveloping chitin cuticle, in conjunction with the tracheal system and the gut lining, serve as major physical barriers to entry.

Secondly, hemolymph itself plays a key role in repairing external wounds as well as destroying foreign organisms within the body cavity.

[1] Social insects additionally have a repertoire of behavioural and chemical "border-defences" and in the case of the ant, groom venom or metapleural gland secretions over their cuticle.

It not only plays an indirect role in defense as individuals prepare themselves physically to take on the task of avoiding predation through camouflage or developing collective mechanical traits to protect a social hive, but also a direct one.

For example, cues elicited from a predator, which may be visual, acoustic, chemical, or vibrational, may cause rapid responses that alter the prey’s phenotype in real time.