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Building a Better Grasshopper Trap: New Design Offers Safer, More Efficient Harvest

Ruspolia differens

In Uganda and neighboring African nations, wild grasshoppers such as Ruspolia differens, shown here in its brown color morph, are a delicacy and are commonly harvested for their use as food. A team of researchers has designed a new trap that improves on the traditional model by reducing nontarget bycatch, energy consumption, and use of hazardous materials. (Photo by Francis Obala)

By Ed Ricciuti

Ed Ricciuti

Ed Ricciuti

Ugandans relish grasshoppers the way Americans gobble popcorn at the movies, and for much the same reason. When deep-fried by someone who knows how, Ruspolia differens grasshoppers—in the family Tettigoniidae, also known as katydids, bush crickets, or long-horned grasshoppers—are as salty, crunchy, and tasty as popcorn ever was, and even more nutritious.

While the idea of insects as an alternate protein source is a tough sell in western nations, Africans don’t need convincing. Across Africa, more than 500 different species of insects are typical table fare, and, for many people, grasshoppers top the menu.

Thus, trapping grasshoppers during their nocturnal migrations is a particularly big business and an avocation in Uganda. Ruspolia differens swarming season there (November to December and March to May) is like deer season in Pennsylvania, as people drop their usual daily routine and set up oil barrels and other metal drums to trap the green or brown insects by night.

grasshopper trap diagram

A team of researchers in Kenya and Uganda has designed a new trap for catching Ruspolia differens grasshoppers that improves on the traditional model by reducing nontarget bycatch, energy consumption, and use of hazardous materials. A LED light replaces a mercury bulb, a funnel atop the drum is used instead of an oil coating on the drum interior to prevent escape, and mesh screens aid in separating nontarget insects from the grasshoppers. (Image by Brian Mwashi, originally published in Sengendo et al 2021 Journal of Economic Entomology)

The traditional method of catching grasshoppers works well enough, but according to a team of scientists based in Kenya and Uganda, it needs an upgrade to improve its efficiency and reduce potential hazards to humans and the environment. So, they have designed, in effect, a better grasshopper trap, which they describe in a new report published this month in the Journal of Economic Entomology. It catches as many grasshoppers as the system already in use but has several advancements, such as being safer and cheaper to operate.

Their tricked-out traps “have better energy-use efficiency and ensure safety to collectors, processors, and consumers,” say the team of researchers from the International Centre of Insect Physiology and Ecology (ICIPE) in Nairobi, Kenya, and Makerere University in Kampala, Uganda.

Traditional traps are nothing more than open drums situated below slanting iron sheets. Part of the setup uses blindingly bright 400-watt mercury bulbs to attract the grasshoppers, which bang against the sheets and slide into the barrels, which are coated on the inside with waste cooking oil to keep the grasshoppers from climbing out and escaping.

It seems easy enough, but the setup has serious drawbacks. Mercury bulbs, for one, can become hot enough to burn the skin and eyes of trappers. When improperly disposed of (as is often the case), mercury from the bulbs can enter the food chain and air. Mercury is a neurotoxin that, once in the human body, can damage the brain and nervous system. Waste oil, which can contain heavy metals such as arsenic and cadmium—known carcinogens—can contaminate the harvest. Moreover, not all insects trapped are grasshoppers. Some, such as the rove beetle Paederus sabaeus—known as the Nairobi fly—are toxic to humans. It secretes pederin, a substance that causes temporary blindness and dermatitis in humans, which is a real danger because the grasshopper harvest is sorted and handled manually. Other nontarget insects, such as night-flying giant water bugs and moths that slip through sorting, can contaminate the edible catch. Scales from moth wings, as well, often mix with the grasshoppers and are almost impossible to remove.

The solution to the problem was as simple as situating a funnel atop the barrel to prevent escapes (rather than coating the inside with oil), changing the bulbs from mercury to LED (which attract just as many grasshoppers but use only half the electricity), and screening out undesirable insects with mesh. “Importantly,” states the paper, “LED 400-watt bulbs attracted the same quantity of R. differens as 400-watt mercury bulbs.” The higher the wattage, moreover, the more grasshoppers were attracted. Screening has a plus in that it is much more efficient than hand sorting. “These advantages of the modified drum increased the safety of R. differens harvesting to trappers, processors, and consumers,” says James Peter Egonyu, Ph.D., a research scientist in ICIPE’s Insects for Food, Feed and Other Uses Programme and senior author on the study.

The researchers modified the trap design as the project unfolded. At first, the barrel had three compartments. The middle was separated from the top with larger-gauge mesh, and from the bottom with smaller. The plan was to filter grasshoppers—called “senene” in Kiswahili and “nsenene” in Luganda, common languages in East Africa and Uganda, respectively—from other insects as they passed through the top mesh into the middle compartment. Smaller insects, such as P. sabaeus, would pass through both screens and end up at the bottom, which is what happened, for the most part.

Although the top mesh was large enough to admit grasshoppers, they remained atop it. Egonyu believes that hairs on the grasshopper’s feet enabled them to cling to the screen. “For this reason, we recommend leaving out the top mesh from the design of the modified drum,” he says.

The researchers advise that the design could still use a little tinkering, to better filter out larger non-target insects for example. They say, however, that it is ready for use as-is.

Egonyu says, “We therefore strongly recommend scaling of this efficient, safe, and environmentally friendly technique of harvesting wild R. differens, not only in Uganda, but also in other countries across Africa such as the Democratic Republic of Congo, Cameroon, Kenya, Tanzania, Malawi, South Africa, Zimbabwe, and Zambia, where this insect is endemic and consumed.”

Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.

2 Comments »

  1. Reducing by-catch and toxicity is certainly laudable. However, why don’t we all just encourage plant-based eating instead? If we keep devising ever-more-efficient methods of slaughtering everything that can look at us for our protein cravings, we’ll soon be eyeing each other as we wipe out all other sentient beings on the planet!

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