But sometimes they can turn into litter: If a drone goes down in a protected area, it might not be possible for anyone to retrieve the hunk of metal and plastic.

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"I have colleagues who do remote sensing in sensitive areas, and there was a UAV lost for a couple months in an area you really wouldn't want to lose one in," said Lynn Rothschild of NASA's Ames Research Center.

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Rothschild serves as an adviser for a team competing in the International Genetically Engineered Machine (iGEM) competition, and the issue of downed-drone-litter seemed like a good one for her group to tackle.

"Normally I just give them free rein, but then there are 15 very bright students who all want to do 15 or 30 different things," she said. "So this year, I suggested an overall project. But they really just ran with it from there."

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One of her students found a company called Ecovative Design that was growing the team's dream material: Blocks of fungal foam.

Mushrooms are made up of a structure called mycelium. It grows looking almost like a spider web when it's spread out, but it can grow to fit the confines it's placed in, eventually forming a tough chunk of foamy material. By putting mycelium into a mold filled with a tasty growing medium -- like dead leaves or straw -- you can create a custom-shaped mushroom block. Or in this case, a custom-shaped mushroom drone frame. A blast of heat kills the mycelium to freeze their growth.

"You end up with this great material that just leftover fungal bits," Rothschild said.

To make the frame more durable, the students created a bioplastic to coat it with.

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You can make a kind of veggie leather using bacteria that create cellulose -- the tough stuff that creates cell walls in plants. The bacterial cellulose is grown in a sheet and harvested, then wrapped around the mycelium frame. When it dries, it's tough and hard.

But the team's biohacking didn't stop there: They also harnessed the power of the insect world to keep their drone from dissolving in mid-air. The drone is covered in proteins cloned from paper wasp saliva, which the insects use to waterproof their nests.

For now, that's as far as the drone's biodegradability goes: It still uses a traditional rotor, battery, and controls. But other researchers around the world are already working on creating biodegradable versions of these components, Rothschild said. And her team is investigating the use of biological sensors, which would allow them to replace some of the sensors on the drone with bacteria.

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"Eventually I'd say that most, if not all, of the drone could be made from biological materials," she said.