The fontanellar gun is a

termite Termites are a group of detritivore, detritophagous Eusociality, eusocial cockroaches which consume a variety of Detritus, decaying plant material, generally in the form of wood, Plant litter, leaf litter, and Humus, soil humus. They are dist ...

defense mechanism In psychoanalytic theory, defence mechanisms are unconscious psychological processes that protect the self from anxiety-producing thoughts and feelings related to internal conflicts and external stressors. According to this theory, healthy ...

in the form of a horn-like frontal projection (''nasus'') on the head of the soldier caste which is capable of expelling chemical weaponry at a distance, a trait exclusive to the subfamily

Nasutitermitinae The Nasutitermitinae is a near Cosmopolitan distribution, cosmopolitan subfamily of Termitidae, higher termites represented by 81 genera and 605 species. The highly derived soldier caste exhibits vestigial mandibles and a protruding Fontanellar ...

. It is primarily used to ward off predators such as ants.

Physiology and usage

The "gun" is a gland with a duct on the front of the head. It operates by a

chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...

triggered when the termite contracts its mandibular muscles. The termite is "able to eject the frontal gland material over a distance of many centimeters". The gland material is forced out through the front of the internal nose and its pores, which covers much of the termite's head. Termites have been shown to be extremely accurate with the gun, even though they are blind. The exact nature of how termites retain such accuracy and are able to orient themselves toward their enemy is currently unknown, but it is believed that the ability is olfactory or auditory in nature. The fired material is glue-like and sticks to objects that it hits, causing the legs of an attacking enemy to become stuck to the ground. Most often, though, a number of termite soldiers will fire upon the enemy and the combined force of the "bullets" will kill the enemy along with covering it in the glue-like substance. It has also been observed that, for those that survive the force of the material, it also causes varying negative effects, likely because of the

terpenes Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n ≥ 2. Terpenes are major biosynthetic building blocks. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predomi ...

contained in the compound. Eventually, if not killed from other effects, the secretion of the termite will kill any enemy insects after 24–48 hours. In comparison, the effect of the secretion on termites of the same species was considerably worse, with the secretion causing death within 5–6 hours.

Chemical composition

The secretion from ''

Tenuirostritermes tenuirostris ''Tenuirostritermes'' is a genus of termites in the family Termitidae Termitidae is the largest family of termites consisting of 2,125 described species of which are commonly known as the higher termites. They are evolutionarily the most spec ...

'' consists of a mixture of three

terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n ≥ 2. Terpenes are major biosynthetic building blocks. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predomi ...

s, namely 62%

pinene Pinene is a collection of unsaturated bicyclic monoterpenes. Two geometric isomers of pinene are found in nature, α-pinene and β-pinene. Both are chiral. As the name suggests, pinenes are found in pines. Specifically, pinene is the major comp ...

, 27%

myrcene Myrcene, or β-myrcene, is a terpene, monoterpene. A colorless oil, it occurs widely in essential oils. It is produced mainly semi-synthetically from ''Myrcia'', from which it gets its name. It is an intermediate in the production of several frag ...

and 11%

limonene Limonene () is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the essential oil of citrus fruit peels. The (+)-isomer, occurring more commonly in nature as the fragrance of oranges, ...

. These form a resinous glue resembling

pine resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...

. The secretion contains an

alarm pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

that alerts other soldier termites of an enemy attack and causes them to fire their fontanellar gun. It was discovered that the pinene was also acting as an alarm pheromone while it was forming the composition of the terpenes. Because later arriving termites did not also fire their gun, it is believed that the pinene pheromone lasts for only a brief period of time before dissipating.

In other termites

The

Syntermitinae The Syntermitinae, also known as the ''Mandibulate nasutes'', is a Neotropical subfamily of higher termites represented by 21 genera and 103 species. The soldier caste of members of this subfamily have a conspicuous horn-like projection on the h ...

, which were once classified within the Nasutitermitinae in a clade known as the ''mandibulate nasute termites'', are now recognized to be a distinct and not closely related lineage which

convergently evolved Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

a nasus that is superficially analogous but not functionally homologous to the nasus of true nasute termites. Unlike true nasutes, all Syntermitinae exhibit soldiers with highly developed mandibles which are physiologically incapable of expelling their frontal gland secretions from the nasus. No other known termite has a frontal apparatus as functionally and morphologically similar to the Nasutitermitinae as the Syntermitinae.

References

{{reflist, 30em Insect morphology Termites