Crickets. They’re not just for reptiles anymore. They’ve been widely touted for being high in protein with a smaller environmental footprint than chicken, pork, or beef. That means they could account for a chunk of the increase in food production that will be necessary to sustain an earthly population that’s projected to reach nine billion by the year 2050.

But researchers at the University of California at Davis published a study this past spring that suggests the story on crickets may be more complicated than at first it seemed.

To be truly sustainable, they need to be fed something more efficient than the same kind of grain-based feed we use for conventional livestock, which uses large amounts of water and fertilizer.

Crickets aren’t picky about their own diet: They’ll eat just about anything. That’s part of what makes them so appealing as “micro-livestock,” in the entomophagic parlance.

Mark Lundy, an agronomist, and Michael Parrella, a horticultural entomologist, wondered if the ultimate nutritional quality of crickets would vary depending on what they were fed. “I wanted to see how efficient they were when you’re feeding them high-quality diets versus low-quality diets,” says Lundy. “Because that’s really where the sustainability questions get sorted out, in what you’re feeding them.”

They gathered 15 large cardboard shipping boxes, then populated each box with 50,000 cricket eggs. After the eggs hatched, the researchers fed them all the same proven cricket feed for a couple of weeks. Then, after day 14, they introduced five different diets (each replicated in three boxes), including standard chicken feed, human food waste that had been processed to different degrees, and plain old straw —with and without poultry manure.

Next, they measured the crickets’ growth—how much “meat” they had packed on by harvest time. The crickets that had been feasting on chicken feed had grown by more than 4,000 percent. Those fed processed food waste grew by some 2,500 percent—there was less meat on their bones, but they were still considered plenty “harvestable.” In the other three groups, all the crickets died before they grew big enough to bother eating.

They concluded that crickets didn’t deliver great sustainability benefits if they were fed chicken feed, since the environmental cost of grain-based feed is so high.Yet, the processed food waste diet held promise. It was provided by a company, called California Safe Soil, that makes fertilizer from leftover produce that would otherwise be thrown away by supermarkets. Their main product is a fertilizer they make using a proprietary process that involves applying enzymes to break down the food waste. At the end of their process, they are left with the fertilizer, plus solids they strained out of it. It’s that solid waste the UC Davis researchers successfully fed to crickets. It was a “soupy solid,” in Lundy’s description, and it even smelled a bit like soup. It’s promising because it was made without additional greenhouse gas emissions, land, water, or fossil fuel-based fertilizers.

For now, this leftover product, which the company calls Hog Heaven because it sells it to one farmer as hog feed, isn’t being fed routinely to crickets. But if it were, the resulting crickets truly would have potential as a more sustainable source of protein than beef, pork, chicken, or even carp. Until that or some other innovation allows large numbers of crickets to be raised without specially-grown grain, eating crickets isn’t going to save the world.

If you want to give crickets a try now, you can cook them yourself, or you can visit one online retailer to choose from salt ’n’ vinegar, barbecue, or chocolate-covered. An Austin company, adorably named Hopper, buys cricket flour and bakes them into granola that’s gluten-free and paleo-friendly. Forty crickets per serving!

But you can’t spell “cricket” without “ick.” The unappetizing idea of chewing up tiny little legs and ingesting exoskeleton, milled into flour or not, means crickets aren’t hopping onto menus in the U.S. with the plague-like fervor all the hype would lead you to expect.

So crickets might not be the chirping silver bullet we’d hoped for, but all is not lost. “I do think that the use of insects is a really promising field,” says Lundy. “It’s relatively under-explored.”

There are other species to consider eating on nature’s vast insect inventory. Black soldier fly, anyone?

Beth Goulart Monson is a freelance food writer based in Austin, TX. Follow her on Twitter.