Caterpillars have long inspired robot designers: their flexible bodies and ability to cling to various surfaces allow them to squeeze through narrow crevices and challenging natural conditions. Recently, a team from the University of Naples Federico II and the University of Palermo set out to find out how well these creatures move across wood, steel, slate and glass.
The work is based on a mathematical model in which the caterpillar's body is represented as a set of masses connected by springs. This model describes how the body bends and interacts with the surface. First, the scientists observed real caterpillars of the species Pieris brassicae (the cabbage white) on different materials, and then tested the model's predictions experimentally.
It turned out that there is a strong correlation between surface roughness and crawling success - a statistical relationship that by itself does not prove causation. The caterpillars easily adapted to most irregularities but had difficulty on smooth glass: the microscopic irregularities there are too small for the prolegs (outgrowths on the body that help it hold on) to grip. This confirms that sufficient traction is critical for starting and sustaining movement.
Building on these data and the model, the researchers created artificial armor that increases the stiffness of the caterpillars' bodies and added weights to improve friction and traction. In experiments that the authors call a proof of concept, such "armored" caterpillars were able to cross smooth glass that is normally inaccessible to them. The results were published in the Journal of the Royal Society Interface.
According to the authors, the work confirms the accuracy of the model and outlines new design criteria for soft crawling robots capable of adapting their movements in complex environments. However, these are still laboratory experiments on insects, not finished devices. Nevertheless, the principles obtained could help in developing robots that will move efficiently across different surfaces, and future research could reproduce the properties of the artificial armor in robotic systems.