The fontanellar gun is a defense mechanism 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 are a subfamily of higher termites that includes more than 80 genera. They are most recognisable by the more highly derived soldier caste which exhibits vestigial mandibles and a protruding fontanellar process on the head ...

. 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 chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...

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 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 '' Tenuirostritemes tenuirostris'' consists of a mixture of three

terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n > 1. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes ...

s, namely 62% pinene, 27%

myrcene Myrcene, or β-myrcene, is a 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 fragrances. � ...

and 11%

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

. These form a resinous glue resembling

pine resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on natu ...

. The secretion contains an alarm pheromone 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.

References

{{reflist, 30em Insect morphology Termites