Scientists have discovered how female sawflies make their precise cuts – a breakthrough that could revolutionise surgical tools and greatly minimise damage to healthy tissue during operations.
The research reveals how these tiny insects use a completely passive cutting system that automatically knows which materials to slice through and which to leave untouched, all without any sensors or computerised controls.
The study, published in Bioinspiration & Biomimetics, demonstrates how the sawfly’s egg-laying organ (an ovipositor) acts like a biological reciprocating saw that instinctively knows when to cut and when to push material aside.
Female sawflies must cut into plants to lay eggs without killing the plant host, which provides food for the developing larvae.
The two-toothed blades slide against each other, but only cut materials with a strength below a certain threshold.
This natural selectivity prevents damage to the vital plant structures whilst allowing the insect to create precise incisions for egg laying.
Dr Martí Verdaguer Mallorquí has been leading the study at Heriot-Watt University in partnership with experts from National Museums Scotland and Senckenberg German Entomological Institute in Müncheberg.
The team also used facilities from the Faculty of Biology at the University of Freiburg in Germany under the leadership of Professor Thomas Speck, Head of the Plant Biomechanics Institute.
Dr Verdaguer Mallorquí said: ‘We’ve discovered something remarkable – a cutting mechanism that essentially thinks for itself. The sawfly’s egg-laying organ can cut through soft plant tissue but automatically avoids the plant's tough internal “plumbing”, including the tubes that carry water and nutrients. This ensures the plant survives and serves as a food supply for the larvae coming from the eggs. This selective cutting occurs purely through the interaction of tooth geometry and composition with the different material properties of the plant. There are no sensors or computers, but rather elegant engineering refined by millions of years of evolution.’
The research team, led by Professor Marc Desmulliez from the School of Engineering & Physical Sciences at Heriot-Watt University, scaled up the sawfly’s cutting mechanism 400 times and tested it on laboratory substrates that mimic human tissue properties.
They found the system operates on an ultimate stress threshold – below this threshold, materials are cut cleanly, but above it, they are harmlessly displaced out of the cutting zone.
Professor Desmulliez explains: ‘This discovery has profound potential implications for surgical practice. Current surgical tools often struggle in complex operations. Surgeons frequently work in blood-flooded environments where visibility is poor and the risk of accidentally cutting vital structures is high. A surgical instrument based on this natural mechanism could instinctively avoid critical tissues whilst cutting precisely where it is needed – essentially giving surgeons a tool that helps prevent mistakes. Further input is now needed from surgeons, but this newly discovered mechanism has tantalising prospects.’
The passive nature of the sawfly’s cutting mechanism is particularly valuable for surgical applications.
Unlike complex robotic systems that require sensors and computational control, this bio-inspired approach achieves selectivity through pure mechanical design. The research suggests that surgical saws and scalpels based on this principle could combine the precision of scissors with the safety benefits of electrosurgical tools, without the thermal damage risks associated with them.
Dr Verdaguer Mallorquí added: ‘What’s particularly exciting is that this mechanism seems to work across multiple sawfly species, each adapted to different plant types. This suggests we could develop a range of surgical tools, each optimised for different tissue types or surgical procedures, all based on these natural cutting systems that have been perfected over millions of years.’
