The complicated process of catheterizing — inserting a thin, flexible tube into a medical patient for diagnostic or therapeutic purposes — may soon be made easier thanks to an unexpected model: the beetle penis.
The sexual organ of the thistle tortoise beetle (Cassida rubiginosa), a Eurasian-native green leaf beetle originally introduced to New Zealand to control invasive Canada thistle, has caught the attention of scientists for its unusual shape and structure. Though the female beetle’s sexual organ is unusually complicated — both long and spiral in shape — damage to and breakage of the male’s appendage is exceedingly rare.
To find out why, researchers from Kiel University in Germany harvested 10 thistle tortoise beetle penises and subjected them to a variety of strength and flexibility tests, as outlined in a December Science Advances study.
“As far as we know, there are no studies that apply a bending test for such a small biological structure,” lead study author Yoko Matsumura toldDiscover. “So we had to design our experimental setup and create tools to carry out the experiment completely by ourselves.”
The researchers measured the organ’s stiffness in 300-micrometer segments under a microscope, finding that the penis — which is longer than the beetle’s body — was stiffer near the base and more flexible at the tip.
“The relatively low bending stiffness of the flagellum’s apical part is advantageous for the flagellum, allowing it to fit into the strongly spiraled spermathecal duct of the female,” the researchers wrote. “On the other hand, the relatively high bending stiffness of the rest of the flagellum enables it to efficiently transfer the penetration force applied to the proximal end of the flagellum.”
The researchers also noted that the member had a soft inner curve, made from a rubberlike protein called resilin, and harder outer curve. This composition, along with its cylindrical shape, maybe what lends the organ its remarkable resilience.
“The animals can achieve the penetration of a delicate and elongated structure into a very complicated duct with very rare breakage,” Matsumura said. “We hope that our finding will help improve medical tools — for example, medical catheters.”
Catheter use in medical settings is rife with complications. Bloodstream infections caused by catheters reportedly cause 28,000 ICU deaths a year, and UTIs due to urinary catheters are the most common healthcare-associated infection, according to the CDC. A smaller, more efficient catheter could make insertion and removal faster and easier, which in theory could cut down on the potential for bacterial contamination.
“The biggest drawback of catheter use is possible health complications caused by different factors. As one of the factors, inaccurate catheter tip location is discussed. Although there are constraints for changes of the catheters’ design due to the complexity and diversity of catheter usage, the self-controlling system of the beetle flagellum position can be potentially applicable,” the researchers wrote.
The findings of the thistle tortoise beetle organ can now be synthesized with the results of other beetle and insect penis experiments, of which apparently there have been quite a few.
"I study the penises of many insects," Matsumura told NPR.
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