Superworms: The Bigger, Brawnier, Hungrier Cousins of Yellow Mealworms

By Ed Ricciuti

Look out, yellow mealworm—you have competition. A bigger, brawnier cousin could threaten your position as a go-to food for backyard bluebirds, pet parrots and lizards, and even tree shrews in zoos, as well as a potential protein source for people, farmed fish, and livestock. Even your reputation as top trout bait could be threatened.

So say Greek scientists who reviewed research on Zophobas morio, the so-called “giant mealworm” or “superworm,” in a paper published in April in the open-access Journal of Insect Science. They deem Z. morio to be “a well-promising insect-based protein source,” whose potential still remains to be seen. However, there is even more to it than that. This species also shows promise for use in animal health and coping with the world’s plastic waste problem. The look at Z. morio is part of a new special collection in the Journal of Insect Science, titled “Insects as Food and Feed: If You Can’t Beat Them, Eat Them!”

A caveat about nomenclature is required here. “The term ‘giant mealworm’ is used also to describe juvenile hormone–treated larvae of the yellow mealworm (Tenebrio molitor),” says Christos I. Rumbos, Ph.D, who authored the paper with Christos G. Athanassiou, Ph.D., both of the University of Thessaly in Volos, Greece. The hormone prevents the yellow mealworm from pupating, and thus prolongs growth. In the case of Z. morio, pupation can be delayed merely by overcrowding. Both mealworms are larvae of different darkling beetles (Tenebrionidae). Zophobas morio adults measure up to 57 millimeters long, while T. molitor is virtually a black speck by comparison at only 12 to 25 millimeters.

Both Zophobas morio and Tenebrio molitor are darkling beetles (Tenebrionidae). Zophobas morio adults (shown here) measure up to 57 millimeters long, while T. molitor adults range from 12 to 25 millimeters. (Photo by Christos I. Rumbos, Ph.D.)

Christos I. Rumbos, Ph.D., is a postdoctoral researcher at the University of Thessaly in Volos, Greece. He and colleague Christos G. Athanassiou, Ph.D., study the mass production of mealworms for uses as food and feed. Here, Rumbos inspects insect rearing trays at the university. Rumbos and Athanassiou organized a new special collection on insects as food and feed in the open-access Journal of Insect Science. (Photo courtesy of Christos I. Rumbos, Ph.D.)

Zophobas morio is consumed by humans in some countries, such as Mexico and Thailand. Superworms are also sold extensively by pet stores as treats for lizards and some birds. The authors, however, believe superworms deserve much more attention.

“The aim of this paper is to highlight the significance of a usually overlooked insect species,” says Rumbos. “Although a tremendous amount of research is directed to the relative species Tenebrio molitor (yellow mealworm), Z. morio has not attracted so far the attention that we think it deserves, not only in terms of research but also from the regulatory authorities.”

Just this January, the European Union declared yellow mealworms as safe for human consumption. The authors stress that the rules governing the use of insect-based products for food must be adjusted to include the superworm for it to realize its potential.

After their extensive review, Rumbos and Athanassiou opine that recent studies “show that Z. morio can be a valuable nutrient and antimicrobial source that could be utilized further in insect-based feed and food production.” Feeding trials, they say, have shown that the superworm has great promise in aquaculture, “both in terms of fish development and health.” Other research suggests that it has comparable value to other insects for feeding poultry.

Studies cited by the authors show that superworms are rich in nitrogen, fatty acids, and amino acids that are the building blocks of protein and energy-producing omega-6 linoleic acid. And that’s just for starters: Superworms also seem to promote the growth of probiotic bacteria and thus help shield against pathogens.

“Zophobas morio larvae are a valuable, largely unexploited source of antimicrobialpeptides with antiradical activity; therefore, their consumption could potentiallyhave an immune-triggering and health-promoting effect,” write the authors. The superworm might provide an alternative to the use of antibiotics to keep chickens farmed for meat disease-free.

Other research has shown that Z. morio hemolymph, the insect equivalent of blood, can effectively protect mammary epithelial cells of cattle against bacterial infections, suggesting its potential to fight bovine mastitis, the most prevalent disease affecting the dairy industry worldwide. “The spectrum of Z. morio applications,” the authors conclude, “is continuously growing.”

Larvae of the darkling beetle Tenebrio molitor (shown here) are known as yellow mealworms, and they are widely studied and mass-produced for various animal-feed uses. And, in January 2021, the European Union declared them safe for human consumption. However, a larger relative, Zophobas morio, offers similar potential but has not received the same research and regulatory attention. (Photo by Christos I. Rumbos, Ph.D.)

Larvae of the darkling beetle Tenebrio molitor (adults shown here) are known as yellow mealworms, and they are widely studied and mass-produced for various animal-feed uses. And, in January 2021, the European Union declared them safe for human consumption. However, a larger relative, Zophobas morio, offers similar potential but has not received the same research and regulatory attention. (Photo by Christos I. Rumbos, Ph.D.)

A huge bonus that comes with using mealworms of either species as animal feed is that the worms themselves are living waste eliminators, capable of eating, biodegrading, and mineralizing various types of plastics, such as polystyrene or polyethylene. In effect, they can nosh on Styrofoam cups and still be safe to feed animals. In fact, research reported last year demonstrated that Z. morio consumes plastic foam at a rate four times higher than does the yellow mealworm.

“These new findings,” say the authors, “are of high importance for plastic waste management and could offer a reliable solution to the problem of plastic accumulation, which represents a global issue of major environmental importance. … Further research is needed to fully unfold the potential applications of this species and optimize its farming systems at an industrial scale.”

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.