#03 2022

Developing a positive space for locusts in the anthropogenic world

By Joh Henschel, Research Associate, SAEON Arid Lands Node

Locust swarms are adorning the Karoo veld again, stirring all sorts of emotions in all and sundry. Such mass events following so shortly on dire droughts are truly awesome, no less now than when Anders Sparrman described this spectacle in 1785 and noted that locusts revitalised the veld by stimulating new growth that followed their passage (Box 1). Back then, people considered eating locusts a “high treat” (in Sparrman’s words), today rendered unpalatable by insecticides.

The grazing lawn of solitary locust females at an egg bank is characterised by short tufts of haasgras Enneapogon desvauxii (Photo: Joh Henschel)

Brown locust female grazing (Photo: Joh Henschel)

Frass pellets accumulate on locust feeding grounds but disappear after rain (Photo: Joh Henschel)

A different set of culturally entrenched opinions regard locusts as a terrible plague, a problem perpetually eliciting crisis management entailing dispensing insecticides with generous government support. However, are brown locusts really a plague? The answer to that is unclear without a proper cost-benefit study of brown locust outbreaks. Such a study would examine, quantify, evaluate and document the economic and ecological dimensions of solitary and gregarious locusts, balancing negative impacts against the positive on a short-term and long-term basis. But this has never been done.

There is, therefore, no proper justification for the ongoing costly and environmentally destructive application of insecticides across the Karoo. Furthermore, locust control measures are conducted blindly as long as key elements of locust ecology remain unknown, as was already highlighted at a locust conference in Kimberley 35 years ago (Henschel, 2015).

When males find foraging solitary brown locust females, they mate (Photo: Joh Henschel)

Females place their eggs into egg cases placed into burrows where the eggs stay until trigger conditions cause synchronous hatching (Photo: Frances Duncan)

Earlier this year, ten institutions, including NRF-SAEON, discussed forming a brown locust research working group to plan a research programme in coordination with farmers, other stakeholders and the government. The initiative, spearheaded by rangeland managers and chaired by the Agricultural Research Council (ARC) at the University of the Western Cape, aims to address critical gaps in the light of existing knowledge. The goal is to inform the development of an integrated locust management strategy.

A century ago, scientists found that the objective to eliminate the brown locust once and for all was futile. Faure (1923) noticed that besides the conspicuous gregarious phase that occasionally roamed far afield across southern Africa, these locusts also had a small, cryptic solitary phase confined to the arid interior Karoo. Once Smit (1939) had established that these solitary grasshoppers gave rise to the gregarious phase in a process closely connected to particular veld conditions that were subject to farming practices, the scene was set to gain the knowledge to manage locust populations through appropriate rangeland management. Alas, this insight has since been ignored, waiting to be tackled by rangeland scientists working together with entomologists and farmers.

Gregarious brown locust hopper bands eat different vegetation than their solitary predecessors, such as this long grass (Photo: Joh Henschel)

They also debark Pteronia pallens, shrubs that are unpalatable and poisonous for livestock, and could thereby improve the veld for livestock farming (Photo: Sue Milton-Dean)

Recently, I observed solitary brown locusts in the veld. I watched females feeding exclusively on short-leaved eight-day grass (Enneapogon desvauxii, colloquially known as “haasgras”), which quickly regrows or sprouts after the smallest amount of rain. Although females defended patches of this grazing lawn, they allowed males to approach to fertilise their eggs laid in what turned out to be the heart of a five-hectare outbreak centre. After emerging hoppers had swarmed across the site, I noticed how much frass (locust dung) was strewn in their wake. When I returned three weeks later, after a light rain had fallen, the frass pellets had disappeared, evidently disintegrated into the topsoil, probably fertilising the booming growth of the many seedlings and regrowth I saw.

The locust research working group will hopefully help replace the plethora of media-hyped orthopterophobic misperceptions concerning Karoo brown locusts with facts based on research and population monitoring. The research gaps that could be addressed include a) the characteristics and functioning of egg banks loaded by solitary locusts at the core of outbreak centres, b) the grazing impacts, nutrient recycling, plant regrowth and food web dynamics of locusts, c) how rangeland management affects outbreak centres, d) applying locust swarm controls without collateral damage, e) analysing diverse perceptions that people have towards locusts. Improved knowledge of these aspects should help inform a cost-benefit study and the development of an integrated locust management plan.

By recognising locusts as integral parts of Karoo biodiversity, people can also discover opportunities they can offer in terms of food and fodder, inspiration for artists, tourist attractions, and fascination for orthopterophilians. Research and monitoring programmes should provide rangeland managers with know-how to manage their veld in such a way that locusts are regarded as useful. Thereby it will be possible to grant locusts positive space in our world.

Sparrman (1785) noted changes that follow the passage of locusts in the Karoo: “The ground is… stripped quite bare; but merely in order that it may shortly afterwards appear in a much more beautiful dress, being, in this case, decked with many kinds of annual grasses, herbs and superb lilies, which had been choked up before by shrubs and perennial plants. These last, moreover, which, throughout the whole of the preceding year, were hard, dry, withered, and half dead, of a pale yellow colour, harsh, and unfit for fodder, have now an opportunity of springing up again, so as to produce with their young shoots and leaves, pastures adorned with a delightful verdure for the use of the cattle and game.”

Box 1: Sparrman, A. 1785. A Voyage to the Cape of Good Hope, towards the Antarctic Polar Circle, and round the world, from the year 1772 to 1776. G.G.J. & J. Robinson, London.

Trophic cascade: this sand snake caught a sand lizard feeding on a poisoned brown locust hopper (Photo: Joh Henschel)

Further reading

Faure, J. C. 1923. The life-history of the brown locust Locustana pardalina (Walker). Science Bulletin of the Union of South Africa Department of Agriculture 1923:205-224.

Henschel, J. R. 2015. Locust times – monitoring populations and outbreak controls in relation to Karoo natural capital. Transactions of the Royal Society of South Africa 70:135-143.

Smit, C. J. B. 1939. Field observations on the brown locust in an outbreak centre. Science Bulletin of the Union of South Africa Department of Agriculture 1939:1-143.