Thomas Eisner/Cornell University
	A bombadier beetle sprays boiling hot liquid from the tip of its abdomen in a defensive response that scientists are studying as a model for possible device for re-lighting gas turbine engines at high altitudes and low temperatures.

Methods used by beetles to defend themselves from predators are providing inspiration for researchers working on everything from robots that crawl through intestines to devices for restarting aircraft engines.

The palmetto beetle, for instance, is a small blue beetle found in the southeastern United States that can cling tenaciously to palmetto leaves when under attack.

Its secret is on the bottom of its foot pads -- a total of 60,000 tiny bristles. When the beetle presses the bristles against the surface and secretes an oily substance, it can strongly adhere to surfaces.

As Thomas Eisner, a chemical ecologist at Cornell University reported in 2000 in the Proceedings of the National Academy of Sciences, the beetle can withstand forces equal to 60 times its body weight for two minutes or more. For shorter periods of a few seconds, it can withstand forces equal to 200 times its weight.

Metin Sitti, director of the NanoRobotics Lab at Carnegie Mellon University, hopes to mimic the beetle's adhesive foot pads as he designs a robot that can maneuver inside the human bowel. The bristles would be fashioned out of polyurethane, silicon rubber or various biocompatible polymers; silicon oil might substitute for the beetle's secretions.

Sitti had previously studied the adhesive abilities of the gecko lizard, which can stick to surfaces even better than a beetle. The gecko also has hairy footpads, though its bristles are much finer than the beetles'. When the gecko presses its foot against a surface, the bristles so closely conform to the surface that they adhere through the van der Waals force ---- a weak electrodynamic force that acts only when molecules are in very close proximity to each other.

The larger bristles of the beetle are unable to take advantage of van der Waals force. In the beetle's case, the addition of a small amount of liquid causes adhesion through capillary force ---- surface tension causes the liquid to be drawn to the tips of the bristles.

For an intestinal robot, this type of adhesion would allow the device to stop itself or creep along the intestinal wall while exerting little physical pressure and therefore consuming only a small amount of its limited battery power.

Eisner's work with the palmetto beetle also inspired Cornell bioengineer Paul Steen and his colleagues to develop "capillary switches" -- actuators without moving parts that can move small quantities of fluids. These switches might be used for chip-based devices that could analyze blood samples or other liquids.

Another study by Cornell's Eisner in 1999 focused on the bombardier beetle. This African insect, known as Stenaptinus insignis, lives on the ground and wards off attacks by squirting predators with a high-pressure jet of boiling hot liquid from the tip of its abdomen.

The liquid actually is sprayed as a series of rapid pulses, which led Andy McIntosh, a combustion scientist at the University of Leeds, to wonder if the beetle's ejection mechanism might serve as a model for a device for re-lighting gas turbine engines at high altitudes and low temperatures.

McIntosh is leading a three-year effort sponsored by the United Kingdom's Engineering and Physical Sciences Research Council to see if knowledge gained from the beetle could aid in developing a pulse combustion device that would shoot high-temperature plasma into an engine's combustion chamber.

-- Byron Spice