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Like the names of the reptiles, turtle beetle larvae have protective coverings. But rather than living under domes of bone and keratin, their shields are made of humbler materials: feces and discarded skin.
Many insects – especially in their forms – have created habitats for themselves. Caddisfly larvae make tubes of stones and sticks, while other larvae crawl along silk covered with debris.
But most of the approximately 2,700 species of Cassidinae (turtle beetles), a family of the leaf beetle group Chrysomelidae, use an extreme form of recycling. Their larvae create a variety of shield-like structures using frass, or fecal matter, and exuviae, or shed exoskeletons.
In a new study published on August 30 in the journal ZooKeysThe researchers looked at the structure of the dung shields in four species of tortoise beetles: Calyptocephala is rare, Cassida sphere, Coats with a hood, and one unknown species. Their observation gives insight into how the caterpillars use and maintain these unusual scatological structures.
Related: an insect that flies with fat on its buttocks is the first known example of ‘superpropulsion’ in nature.
Some leaf beetles may start their life in the soil – in some species, the mother beetle covers her eggs with litter to protect them before they hatch. This can transfer beneficial bacteria. In turtle beetles, the mother may leave her eggs exposed or hide them in an ootheca, or protective enclosure, sometimes decorated with fecal pellets.
After hatching, some species begin to form their fecal defenses immediately, using their unusual telescopic anuses. These appendages are long and can be manipulated from the body to place their bowel movements on top of their caudal processes – jointed structures that protrude from the back.
Some species, which use only their old skins, wait until their first shed begins to form a shield. They shed the discarded skin mostly down their stomachs, keeping the shriveled husk at the tip.
In both cases, larvae maintain this shield with each successive molt. Some species combine their exoskeleton with feces, ending up with a mound of poop-encrusted exoskeleton right at their rear ends. Despite the seemingly unwieldy nature of this structure, they are able to drive it, which he holds well over all their bodies like a dung parasol.
When the researchers removed the shields of many larvae, the analysts began to replace them as soon as they produced more droppings. They also repaired their shields when they were damaged, pouring more feces into the broken areas to balance the load.
“Obviously symmetry is important and they can figure that out,” the lead author said Caroline Chabooresearch assistant at the Nebraska Museum at the University of Nebraska-Lincoln, told Live Science.
Researchers have suggested a number of reasons for this technique of using feces. Another theory is that it may protect the delicate larvae from the cold, preventing them from drying out or getting too warm.
“Evolution, what I’m looking at is the transition from leaf mining – living inside the leaves – living openly on the leaf,” said Chaboo, referring to the fact that most Chrysomelidae larvae tunnel through plants. “That’s a very different habitat in terms of physical parameters: temperature, humidity, sunlight.”
Shields can also be a form of balance. They look like bird droppings so they are not attractive to most predators. “Secondly, these structures can act as a barrier to predators and parasites,” Chaboo said.
Some turtle beetles also appear use liquid drops by using their tight butts. These droplets may contain toxins that they release from host plants as another deterrent. “The nasty chemicals they use are volatile and leak into the air, so they have to pass them on,” he said.
Many beetles retain their shields as they grow, protecting them as they metamorphose. However, adult cockroaches do not go through private rooms. They really are like turtles – their wing covers are always beautiful and iridescent and rounded at the top and flattened at the edges. They tuck their legs and bodies under this jewel-toned armor for protection – perhaps a relief after months of hunting under piles of poo.
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