A team at the University of Southern California has achieved that goal, creating an 88-milligram robot, the "RoBeetle," that runs on methanol and uses an artificial muscular system to crawl, climb, and carry weight for up to two hours.

The beetle-shaped device is just 15 millimeters long, making it one of the lightest and smallest autonomous robots ever created, its inventor Xiufeng Yang told AFP.

We wanted to create a robot that is similar in size and weight to real insects, added Yang, the lead author of a paper published Wednesday in the journal Science Robotics describing the invention.

The problem with the manufacture of these types of devices is that most robots need motors that are heavy and need electricity, which requires adding batteries.

The smallest batteries available weigh between 10 and 20 times what a tiger beetle weighs, a 50-milligram insect that the team used as a reference.

To overcome that stumbling block, Yang and his colleagues devised an artificial muscular system based on liquid fuel, in this case methanol, that stores about 10 times more energy than a battery of the same size.

Those muscles are made up of wires made of a nickel-titanium alloy whose length contracts when heated, unlike most metals, which expand at higher temperatures.

The creators of the RoBeetle covered those cables with platinum powder that acts as a catalyst for the combustion of methanol vapor.

As the vapor from the robot's fuel tanks burns into platinum powder, the cable contracts and a set of microvalves closes to stop combustion.

The cable then cools and expands, which reopens the valves. The process is repeated until the methanol reservoir is exhausted.

The contraction and expansion movement of these cables is connected to the front legs of the RoBeetle through a transmission mechanism that allows it to crawl.

The team tested their robot on flat, sloping surfaces made of smooth materials, like glass, or rough, like the top of a mattress.

RoBeetle can carry up to 2.6 times its weight and run for two hours on a full tank, Yang explained.

For comparison, the smallest four-legged battery-powered robot weighs one gram and runs for about 12 minutes.

In the future, these minirobots may be used for tasks such as infrastructure inspection, rescue missions after natural disasters or for artificial pollinations.

Robotics experts Ryan Truby and Shuguang Li, from MIT and Harvard University respectively, noted in a written comment that the RoBeetle is an exciting achievement for micro-robotics, although they assured that it still has room for improvement.

The absence of electronics in the robot and the fact that it can only move forward reduces its ability to carry out sophisticated tasks, they noted.