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Further vernacular names:

Green Thistle Beetle

Classification:

Cassida rubiginosa belongs to the subfamily Cassidinae, tribe Cassidini.

Distribution:

Palearctic (Europe, Asia, North Africa), North America.

Habitat:

On moderately fresh to moist meadows, in reed beds and in extensive fields.

Description:

Size 6 - 7.5 mm; elytra and pronotum form a wide shield covering the body; pronotum monochrome green; elytra in fully colored animals with red or yellow-brown basal triangle and 4 basal spots and a distinct spot behind the shield; elytra without black spots on the shoulder bulge; lateral margin of the elytra bent and flattened, edge of lateral margin not thickened in the middle; elytra with ± irregular dot stripes, at least in the 3rd and 4th space there are surplus dots; clypeus black; forehead narrow, more than 1/4 longer than broad; legs mostly yellow, at least the 1st third of the femora black; claws toothless at the base.

Biology:

The Thistle Tortoise Beetle Cassida rubiginosa is an oligophagous species living on composites (Asteraceae: Carduinae). In Central Europe the beetles are found on thistles (Carduus, Cirsium, Silybum), burdock (Arctium) and knapweed (Centaurea).
Cassida rubiginosa forms one generation per year. The adults overwinter and appear in early spring. A female lays about 800 eggs. The eggs are laid in small groups near the tip of a leaf and covered with a reddish-brown secretion. After hatching, the larvae, like the imagines, live and feed on the leaf surface. The greenish or brownish colored larvae carry a shield of faeces and old larval skins, which serves as protection against parasitoids. The pupal period lasts about 8 days. In early summer the new generation of Cassida rubiginosa hatches. The beetles feed on their host plants until autumn and hibernate after maturation feeding.

Natural enemies:

The tachnids Dufouria chalybeata (Meigen, 1824) and Eucelatoria dimmocki (Aldrich, 1932) (Diptera: Tachinidae).
Some parasitic wasp species from the families Eulophidae, Chalcididae, Eupelmidae, Mymaridae, Tetracampidae, Trichogrammatidae, Ichneumonidae.
Cerceris albofasciata (Rossi, 1790) (Hymenoptera: Crabronidae: Philanthinae) - Cerceris albofasciata is a predator of tortoise beetles (Cassidinae). The captured beetles are paralyzed and brought into the nest by the females as food for the larvae.

References, further reading, links:

1. Rheinheimer, Joachim, & Hassler, Michael: Die Blattkäfer Baden-Württembergs, 2018, 928 pages, Kleinsteuber Books (Karlsruhe), ISBN 978-3-9818110-2-5
2. Arved Lompe: Die Käfer Europas - Ein Bestimmungswerk im Internet