Insects are a source of versatility, ideas and concepts.
Every insect is encased within a layer of cuticle, a fibrous composite. Without much variation in density or chemistry its modulus ranges across seven orders of magnitude. The softest cuticle is on the body of the female locust. It stretches up to 15 times its original length when the female locust digs a deep hole in which to lay her eggs. It’s the digger at the end of the body that pulls, so the cuticle has to be soft – less than 1 kPa. It’s a gel. At the time I was more interested in the cuticle, but worked out as a side project how the digger works as an autonomous excavator. I published my analysis of it in 1976.
Years later I was again interested in making holes – this time it was wasps (not the garden stingers) drilling holes in wood to lay their eggs. I was in New Zealand where wood is important, so these drilling wasps are of commercial interest since their larvae make holes in the wood and reduce its value. That meant, of course, that we couldn’t get any live wasps to study – they had all been zapped! But we could work out the drilling mechanism from the morphology.
Actually, forget drilling. You’re probably thinking of some sort of twist drill, and wasps don’t twist. They reciprocate. The ‘drill’ is in two longitudinal halves, closely interlocked and able to slide, like a zip-lock on a plastic bag. It’s a pushme-pullyou device with teeth at the tip pointing backwards, so that as one half of the drill is pushed into the wood, the other half grips the sides of the hole and is pulled. Zero net force. Like the Bowden cable actuating the brakes on your bike, the wasp’s drill can be as long as it likes and will not buckle. There are, of course, some cutting teeth on the drill (now recognised as a sort of pull-saw) and even little pockets to remove the sawdust! One of the wasps we looked at was a parasite of the larvae living in the wood, so it needed to steer its drill towards its prey when it detected it.
Move on another ten years and I get a phone call from a team based in a London college preparing a bid to the European Space Agency for a machine to sample the surface of an asteroid. Had I any ideas? With its zero-insertion force the wasp drill would work in zero gravity, and the concept was accepted. Two weeks later a phone call came from an Italian consortium bidding for the same ESA contract. With the agreement of the London team, I suggested the locust excavation machine. The ESA had eight bids submitted. Their plan was to award the contract to one of them. But they liked the two insect diggers so much that they awarded contracts to both.
A few years later I was giving a talk to some engineers at Imperial College and included the wasp story. Ferdinando from the medical robotics department was in the audience. He wanted to invent a steerable intracranial endoscope. And here was his concept – a steerable probe with zero-insertion force. We had a couple of pub sessions, put together a plan, and 13 years later Ferdinando had developed a new medical device. Whilst the wasp delivers eggs down the drill tube, Ferdinando’s device carries a video camera, can do microsurgery and more – the video below tells the story.
It took about 145 M years to develop such versatility.
This article first appeared in Professional Engineering No 5, 2022