Again they compared plants with their spines intact and removed, but this time they measured how long it took caterpillars to remove all of a plant’s leaves rather than speed to the leaves at the top. The three species vary in spine density: Ethiopian nightshade has the fewest, while the purple devil has the most. aethiopicum, the Ethiopian nightshade, and S. Lastly, they expanded the research to include two other species in the same genus: S. Then they went a step further by manipulating the spine density, slicing away spines with a razor blade so that all the plants had the same number, and repeated the experiment. After removing all of a plant’s leaves save the freshest, tastiest one at the top, they placed caterpillars on the soil next to the plants’ stems and clocked how long it took the bugs to reach the tasty morsel above, comparing inbred plants to normal ones. carolinense variety - which has fewer spines than genetically normal plants do - they examined the effects of spine density on caterpillar movement. To test whether that was so, Mescher explained, the team designed a set of experiments that could explore the question three ways. Surely the tiny caterpillars could simply climb around or over the horsenettle’s spines. From an ecological perspective, it’s wasteful for a plant to expend energy growing a structure like a thorn unless it thwarts the attacker at hand. But seeing caterpillars have the same effect raised a flag for Kariyat and Mescher. Researchers had documented other plant species that grew extra thorns in response to predation by mammals. “That made us think that these spines could also have additional function than what we have been taught,” Kariyat said. After tobacco hornworm caterpillars ( Manduca sexta) fed on the plants, new shoots sported more spines. As a doctoral student at Pennsylvania State University, he was working with Mark Mescher (also now at ETH Zurich) on the genetic consequences of inbreeding and herbivory on Carolina horsenettle plants ( Solanum carolinense) when the pair noticed something strange.
![plant with leaves that have small soft thorns plant with leaves that have small soft thorns](https://fps.ucdavis.edu/images/brandy.jpg)
Rupesh Kariyat, an ecologist studying plant-insect interactions in the biocommunication group at the Swiss Federal Institute of Technology Zurich (ETH Zurich), didn’t set out to upend the conventional wisdom about plant spines. The counterintuitive results show the pitfalls of trusting human experience and intuition too much when trying to understand the evolutionary dynamics of other species in a prehistoric world.
![plant with leaves that have small soft thorns plant with leaves that have small soft thorns](https://mongabay-images.s3.amazonaws.com/rainforests/photos/costa-rica_0959_4x3.jpg)
Now, a report in Biology Letters suggests that, at least for some plant species, spines play an important role in defending against insects - a hypothesis that has long been ignored if not dismissed entirely. Moreover, some paleontological work offers evidence that spines evolved before the first plant-eating terrestrial animals did. Over the years, studies of how well sharp deterrents discourage hungry mammals have returned mixed results. The overwhelming bulk of the scientific literature on the ecological and evolutionary purpose of thorniness (or, to use biologists’ preferred terminology, spinescence) has focused on the hypothesis that mammalian herbivores are the main target. For decades, this has been the working assumption of scientists who study ecological interactions between plants and animals. Why do roses have thorns? The answer seems self-evident: Thorns, spines and prickles are plants’ defensive weaponry, making their most precious parts unpalatable - even untouchable - to big plant-eaters, like deer and other mammals.