The use of insect repellents is fascinating throughout the animal kingdom and is thought to have been around for millions of years. Both primates and birds have used naturally occurring repellents during periods of increased biting insect activity. The repellents range from the use of fruits or leaves to the oils secreted by other insects such as millipedes.
Native Americans used root vegetables as either an ointment or fuel for fire to deter insects. Apparently, the use of fringed sagewort was also highly commonplace and believed to be so effective at repelling mosquitoes when burnt that wild horses would shelter in the smoke as well. This led to the natives using it as a means to attract horses in.
This practice of burning fuels is carried on today and is common in all areas of the world where biting insects are a problem. From burning coconuts and papaya leaves in the Solomon islands to a mango wood and ginger leaves in Papua New Guinea, it may be crude but it certainly makes a difference.
Pyrethrum oils are another natural insect repellent with a history. Derived from the seed coating of the pyrethrum daisys, genus Chrysanthemum, found in both Persia and the dalmation coast, it is thought that these plants proliferated along the caravan routes of the ancient world into Asia. Popularlised through its inclusion in incense sticks, pyrethrum is now used not only for Hindu or Buddhist ceremony but also as day to day insect repellent.
In its powder form, pyrethrum was used by Napoleon and in World War 2 to protect from lice and fleas. The powder is still the active ingredient in the 30 billion mosquito coils sold each year, which evolved from incense sticks. The trouble is the coils are toxic and you cannot safely be in the same room as them, which, although more expensive, makes incense sticks a better option.
Herodotus, who noted that in ancient Egypt, the oil of a particularly awful smelling castor-oil plant was burnt in lamps, made the first recorded human use of an insect repellent. This observation also included documenting the use of rudimentary bed nets too.
In ancient Rome, it was de rigueur to apply a vinegar concoction, especially on the head and feet to ward away insects. It is thought this would have masked the kairomones of the Romans as well as repelling the insects. Practices also included the burning of herbs such as oregano and black cumin.
In various documentations from other civilizations, the practice of burning things seems rather prevalent. The general idea seems to have been to burn anything that made a smell. Sources have shown the use of fish, snakeskin even feathers. Some cases show the use of asafoetidia, which in old French is known as Devil’s dung for the pungency of its odor. In reality, the fumes would have been highly noxious and wouldn’t have repelled insects especially effectively. However, they have masked the human kairomones and created convection currents strong enough to disturb any homing mosquitoes.
Even more interesting are the observations of primates such as the wedge-capped capuchin monkey in captivity. These captive born primates would pick out of a group of filter papers, the one with the benzoquinones found on the Orthorpus dorsovittatus millipede. This shows them to be genetically predisposed to the utilization of insect repellents and that these are exhibited as an extended phenotype or gene that aids their survival.
It is clear that without insect repellents, many species would not have survived until now and that includes us!