Asian elephant (Elephus maximus) fly switching

In 1862, British artist and botanical enthusiast Samuel Peal moved to Sibsagar in northeast India. He took up the colonial practice of running a tea plantation, paying his workers with a mix of money and opium. And on occasion, he rode elephants.

Here he is, writing to the journal Nature in 1879 about the curious behaviour of a female elephant he was riding:

for some moments she moved along rummaging the smaller jungle on the bank; at last she came to a cluster of young shoots well branched, and after feeling among them, and selecting one, raised her trunk and neatly stripped down the stem, taking off all the lower branches and leaving a fine bunch on top. She deliberately cleaned it down several times, and then laying hold at the lower end broke off a beautiful fan or switch about five feet long, handle included. With this she kept the flies at bay as we went along, flapping them off on each side every now and then.

Peal stressed to his readers that this elephant had intelligently made a tool for a definite purpose, an uncommon observation for its time—this is more than eighty years before Jane Goodall reported on her Gombe chimpanzees. He was not the first to take note of elephants getting proactive about pesky flies, though. Forty years earlier, Sir William Cornwallis Harris was hunting in southern Africa (well of course he was, just look at his name), when he encountered wild elephant herds:

Every height and green knoll was dotted over with groups of them…their colossal forms being at one moment partially concealed by the trees which they were disfiguring with giant strength; and at others seen majestically emerging into the open glades, bearing in their trunks the branches of trees with which they indolently protected themselves from the flies.

Harris slots this ‘soul-stirring and sublime’ scene in amongst tales of his mass slaughter of local animals. Peal was more of a naturalist than Harris, a contributor to learned societies and an astute world-watcher. Even so, it took another century before his quick note on elephant branch tool use finally saw serious academic study.

Switch hitting

Let’s fast forward to the early 1990s, then, where we find University of California scientists Benjamin and Lynette Hart at the Royal Chitwan National Park in Nepal. The Park lodges kept 15 Asian elephants to transport tourists, and the Harts were keen to use their time with these beasts to follow up on the earlier anecdotes. They were particularly interested in the proposed link between elephant branch use and flies.

The Nepalese elephants were all adult females. First up, the Harts needed to work out whether switching (or swatting) was actually more common when more flies were around, and not just a way for the animals to keep cool, or a nervous tic resulting from their captivity.

The results were clear. Across more than a hundred 10-minute observation periods, the elephants used a switch at least once every time. At the time of greatest fly intensity, in late morning, the animals were swiping themselves with branches or other items between 55 and 245 times in those 10-minute periods. The temperature didn’t matter, except when it increased fly activity (cool daybreak was the most peaceful time). Leafy branches were a preferred tool material, but vines, bark and even a handy burlap sack were all put to good use:

The elephants often targeted their chest and stomach—the areas that flies liked to congregate—further supporting a fly-reduction role for switching. And compared to times where no tool materials were available, switching almost halved the number of flies on and around the elephants. The same behaviour applied whether the animals were just standing around or moving through the forest, with elephants in the latter case regularly picking up and even trimming branches that they used as fly swats while walking along, essentially replicating Peal’s description.

An added bonus: if a switch tool broke up too much during use, the elephant could (and often did) just eat it.

Making the best of things

In a follow-up study a few years later, the Harts moved south to Nagarhole National Park in Karnataka, India. They wanted to observe wild elephants, and to learn more about tool-manufacture.

Over five days, their research team confirmed that all the activities they’d seen with the captive Nepalese elephants also happened in the wild. These included stripping branches to make switches, eating their tools after use, and sometimes keeping tools around for later re-use. Both adult male and female elephants were active fly swatters, using plant material of around 0.75-2 metres in length.

For example, here’s a wild bull elephant that was feeding on a Ficus, using a branch from the tree as a switch. He later ate it:

Again the Harts had access to nearby captive elephants, this time kept either for riding or for help with logging. They gave these animals long branches of Butea monosperma (or flame-of-the-forest), from which the elephants would typically eat the bark but not the leaves. The branches were around 2.5-4 metres, larger than the preferred size they’d noted for wild elephants.

Eight of the 13 tested elephants modified the branches before using them as a switch. They showed two main methods: (i) removing a side branch by ripping it off using their trunk, often while holding the larger branch down with a foot, and (ii) snapping the main branch—again sometimes using the trunk and foot in combination—to make it shorter, then using the leafy end. An 18-month old juvenile male elephant also used the side-branch-removal technique, as you can see in the image at the top of this post.

Here’s an adult female using her weight to great effect:

We’ve covered this kind of reductive tool-making elsewhere in the animal kingdom, for example with chimpanzees, cockatoos, and even King Kong. Animals seem to be natural subtractors, which marks a point of difference with a lot of human technology. We tend to be natural adders, joining things together even when it’s not necessary or might be inefficient. For instance, a 2021 study published in Nature (the same journal that Peal wrote to 140+ years earlier) found that people typically added blocks to a lego tower to make it stable, despite the simplest option being to remove the one block that made it unstable in the first place.

Observation and speculation

The tale of elephant fly switching started as a couple of nineteenth-century side-notes from people who happened to share what they’d seen. As usual, local people knew all about the behaviour already, but they weren’t in touch with book publishers or scientific journals, and were very likely to be ignored or ridiculed by the western scientific establishment in any case.

Samuel Edward Peal is a good example of the kind of well-connected colonial naturalist with broad scientific interests who parachuted into other people’s lands. He not only reported on animal behaviour, he described a species of keelback snake in Assam that bears his name (Herpetoreas pealii) and that wasn’t seen again for almost 130 years. He also helped identify the tea mosquito bug (Helopeltis theivora), a serious problem for his plantations.

Cases such as Peal’s early record of elephant fly switching might make us wonder why it can take so long for anecdotes to be picked up and studied more closely. But it’s also easy to rely on survivor bias to overlook when early reports were simply wrong. So let’s end here with a cautionary tale that emphasises just why we shouldn’t rush to automatically accept initial reports from enthusiastic amateurs.

In 1886, a few years after his elephant piece, Peal was back in Nature with another commentary. He was adding to a short note by George Darwin, Astronomy Professor at Cambridge University and son of biologist Charles Darwin. Darwin Jr. knew a fair bit about the Earth’s moon: he had proposed (correctly) that it was likely formed from a piece of the Earth itself, although the mechanism he (incorrectly) suggested for its detachment was the early Earth’s rapid rotation.

In his amateur role, Peal wrote to Darwin to outline his theory that the moon’s craters, and in fact all its surface features, were formed and covered by glaciers and other ice. As he relates, the moon’s surface temperature had been falling over time:

until at last the entire globe was cased in ice, the last portions to glaciate being what we call the equatorial seas.

As watery pools on the surface evaporated, with the help of volcanic vents, this moisture

would condense and fall as snow; what fell beyond the lagoon margin would pile to form the ring.

Voila—what we know today are lunar craters were actually circular rings of snow, built up around extinct frozen lagoons.

Peal got this one wrong. While the younger Darwin did not subscribe to this theory, he did refer to it in print, and it actually takes up a larger proportion of the journal than Peal’s prescient elephant note. (Also, being completely fair, there really is surface ice on the moon, but only scattered at the lunar poles.)

All of which is to say that some past reports may have more scientific merit than others. It’s up to the modern inquisitive researcher which ones she chooses to branch out on, and which to leave out in the cold.

Sources: Peal, S. (1879) Intellect in Brutes. Nature 21: 34. || Harris, W. (1838) Narrative of an Expedition Into Southern Africa, during the years 1836, and 1837, from the Cape of Good Hope, through the territories of the chief Moselekatse, to the tropic of Capricorn, with a sketch of the recent emigration of the border colonists, and a zoological appendix. Bombay, Printed at the American mission press. || Hart, B. & L. Hart (1994) Fly switching by Asian elephants: tool use to control parasites. Animal Behaviour 48: 35–45. || Hart, B. et al. (2001) Cognitive behaviour in Asian elephants: use and modification of branches for fly switching. Animal Behaviour 62 :839–847. || Adams et al. (2021) People systematically overlook subtractive changes. Nature 592: 258–261. || Das, A. et al. (2020) Lost and found: rediscovery and systematics of the Northeast Indian snake Hebius pealii (Sclater, 1891). Vertebrate Zoology 70: 305-318. || Dey, A. (2015) Bugs in the Garden: Tea Plantations and Environmental Constraints in Eastern India (Assam), 1840-1910. Environment and History 21: 537–565. || Darwin, G. (1886) Ice on the moon’s surface. Nature 34: 264. || Peal, S. (1886) Lunar glaciation. Nature 35: 100-101.

Main image credit: Hart et al. (2001) || Second image credit: Hart & Hart (1994) || Third and fourth image credits: Hart et al. (2001)