Thistle Tortoise Beetle

The thistle tortioise beetles measure 6.0–8.0 mm in length. Like all Cassida, its head is covered by the pronotum, and the elytra has a wide flange surrounding it. This species is highly rounded, with green or yellowish-green elytra, sometimes with a small, dark triangular spot around the scutellum. The common name may be misleading for the identification of this species as rubiginosus, which is Latin for "rusty or rust-coloured". However, in preserved conditions, the green color quickly becomes brown.

This beetle inhabits North America and can be commonly found from South Dakota to Virginia within the United States. In Canada, it is found across several provinces, spanning from Alberta to New Brunswick. In Europe, it can be encountered from Fennoscandia to Greece and Spain. It is also found in Great Britain and across Siberia. In these regions, they live in areas where there are plenty of thistle. For example, these can include fields, pastures, orchards, meadows, and farmland. The types of thistles they reside on include the Canada thistle, the bull thistle, the musk thistle, the plumeless thistle, and the field thistle.

C. rubiginosa feeds on various Asteraceae, including thistles and many others. Thistle beetle larvae mainly stay on the leaves they were hatched on throughout their development and feed on them. The adults are usually found on the underside of the leaves and the larvae on the uppersides. The time it takes for them to begin feeding depends on a few factors relating to the leaf's structure. The larvae wait until the thistle plants grow by 30% and for the nitrogen levels in the leaves to drop by 50% before feeding. The time that they start feeding also affects the growth of the thistle plant. The plant's upward-growing capability is inhibited when feeding starts late in the season. However, no effect on the plants is detected when feeding begins in the early season. ' Adult feeding can damage the leaves more significantly than larvae feeding since they do not begin eating from the edges of the leaf but instead begin at the center and eat down from the surface. Adults may also feed on pollen of buttercups and ox-eye daisies. The beetle's consumption of these plants is facilitated by a symbiotic relationship with the bacteria Stammera, which is housed in specialized structures within the foregut and allows the beetle to digest pectin, which is indigestible to most animals.