Beetles in the family Chrysomelidae are commonly called leaf beetles. It is the largest of beetle families among the phytophagous (plant-eating) beetles; chrysomelids are second in number of species only to the weevil, 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; i.e. the so-called dogbane leaf beetle, Chrysochus auratus, which feeds on prairie plants such as milkweed (Asclepias sp.) and plants in the dogbane genus Apocynum. [2]

Milkweed leaf beetles are distinctively marked, large orange and black, and are commonly called "swamp" milkweed beetles, after their preference for the swamp milkweed, Asclepias incarnata. There are four species in the genus, but only L. clivicollis lives north of Mexico. The others are distributed throughout Mexico and Central America.

Habitat: Meadows and forest clearings, roadsides / Food: Dogbane and other members of the milkweed family / Life cycle: eggs are laid on the host plant or on the ground; larvae tunnel through soil to roots, feed, and pupate in soil. Adults overwinter inside the shrivelled, woolly leaves of mullein, a weed common to roadsides and waste places. [3]

"Plant chemical defenses can be eaten by herbivores, stored, and used in defense against predators. To be effective defensive agents, the sequestered chemicals cannot be metabolized into inactive products. Utilizing plant chemicals can be costly to herbivores because it often requires specialized handling, storage, and modification (Bowers 1992). This cost can be seen when plants that utilize plant chemicals are compared to those plants that do not in a situation where herbivores are excluded. Caterpillar and adult monarch butterflies store cardiac glycosides from milkweed, making these organisms distasteful. After eating a monarch caterpillar or butterfly, its bird predator will vomit and will avoid eating similar individuals in the future (Huheey 1984). Species that feed on milkweeds are usually aposematically colored. Aposomatic species are those that advertise their distastefulness by being brightly colored (see Guilford 1990). Two different species of milkweed bug in the family Hemiptera, Lygaeus kalmii and Oncopeltus fasciatus, are thus colored, with bright orange and black markings."
From The Wikipedia "Herbivore adaptations to plant defense."

The orange and black aposematic colors are thought to be part of the "Milkweed mimicry" complex which includes Monarch butterflies (Danaus plexippus), Viceroy and soldier butterflies, and the large and small milkweed bugs . All of these creatures are intimately associated with the milkweed plant, Acelpias ssp., in that their larvae feed on the plant, thereby ingesting protective glycosides, or they mimic insects whose larvae do.

Small Milkweed Bug Lygaeus kalmii

Viceroy Butterfly Limenitis archippus

Monarch Butterfly Danaus plexippus

Soldier Butterfly Danaus eresimus

The Large Milkweed Bug, Oncopeltus fasciatus, is a member of the Milkweed Mimicry Complex