Tortoise Beetles – Deloyala clavata / Helocassis clavata and Cassida rubiginosa

Cassida rubiginosa is commonly known as the "Thistle tortoise beetle" – larvae and adults feed mainly on several species of thistle (Carduus, Cirsium, Onopordum spp.) plus knapweed (Centaurea spp.) and a few other weedy composite plants. This is an invasive species, native to Eurasia; accidentally introduced in Quebec in 1901, has since spread east to New Brunswick, west to Alberta, and south to the northern United States. This beetle is said to have been used in biological control of thistles.

Leaf Beetles – Family Chrysomelidae is 2nd largest among the phytophagous (plant-eating) beetles, taking a back seat only to the weevils (Family Curculionidae). There are as many as 35,000 described species and perhaps up to 60,000 total species. Presently, the Chrysomelidae are classified in 195 genera and approximately 1,720 valid species and subspecies (plus 149 Bruchinae species) accepted as occurring in North America north of Mexico. [1]

Leaf beetles feed strictly on plant materials. The adults usually consume leaves, stems, flowers, and pollen. Most larvae are subterranean in habit, feeding on roots and rootlets, but others will consume foliage as well. Many chrysomelids are very specific to particular host plants, but most are able to live on a variety of plants; e.g. the so-called dogbane leaf beetle, which feeds  on milkweed (Asclepias sp.) as well as the dogbane genus Apocynum. [2]

The larval stages of beetles in the subfamily Cryptocephalinae develop inside a case made of fecal material and plant debris, hence their common name "casebearer." They are also known as "cylindrical leaf" beetles. There are approximately 345 species in 22 genera in North America.

Habitat: Meadows and forest clearings, roadsides / Food: Dogbane and other members of the milkweed family / Life cycle: Yellow eggs are laid on the host plant or on the ground; larvae tunnel through soil to roots, feed, and pupate in soil.

Ever since I saw its picture in the Audubon Society's Field Guide, I'd wondered what this "clavate" (meaning, essentially, "thickened at one end") really looked like (their pictures are terrible). I finally saw one on May 22, 2005, then: a mini – population explosion in a patch of wild morning glory. Oh boy. These little guys don't do much that I can tell.

They mostly sit around, flattened against the bottoms of leaves, grinning, looking all the world like bits of snot with general goo mixed in. I have not figured out which end is supposedly thickened. I did find a few willing to get up and walk about – but they never go far without suddenly bursting into flight. And I do mean suddenly; you can't catch them unfurling thier wings, BOOM – they're gone – a few inches away. You be the judge of what evolution was thinking when it spat out these little blobs-of-phlegm.

Thistle Tortoise Beetle – Cassida rubiginosa

References

1. JR, Ross H. Arnett et al., American Beetles, Volume II: Polyphaga: Scarabaeoidea through Curculionoidea, 1st ed.
2. Jürgen Gross, On the Evolution of Host Plant Specialization in Leaf Beetles (Logos, 2001).
3. Kim Fleming, Bugguide.net Casebearing Larva, Anomoea laticlavia
4. Thomas Eisner, Maria Eisner, and Melody Siegler, Secret Weapons: Defenses of Insects, Spiders, Scorpions, and Other Many-Legged Creatures (Belknap Press, 2005).

Order Coleoptera: Beetles are the dominant form of life on earth: one of every five living species is a beetle. Coleoptera is the largest order in the animal kingdom, containing a third of all insect species. There are about 400,000 known species worldwide, ~30,000 of which live in North America.  Beetles live in nearly every habitat, and for every kind of food, there's probably a beetle species that eats it.
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