We all know that monarch larvae eat milkweed plants, but what about the other insects that share a food source with Monarchs?
Red Milkweed Beetle (Tetraopes tetrophthalmus)
Native range: Their range matches the distribution of Common Milkweed (Asclepias syriaca), basically the Northeast quadrant of North America
Harmful to Monarch caterpillars/eggs? No. They are herbivores and only eat milkweed. They are harmless to monarch larvae and eggs so you can leave them on your milkweed plant if you have enough to go around.
Identification: Red/orange in color with oval spots all over body and un-ringed antennae.
Life Cycle: Eggs laid on stems near ground or just below surface; larvae bore into stems, overwinter in roots, and pupate in spring; adults emerge in early summer
Small Milkweed Bug (Lygaeus kalmii)
Native range: Throughout US and Southern Canada
Harmful to Monarch caterpillars/eggs? Sometimes. They are mostly herbaceous and will suck nectar from flowers and sometimes feed on milkweed seeds. However, they have been reported to be predators, especially in spring when milkweed seeds are scarce. They have been reported feeding on honey bees, monarch caterpillars and pupae, and dogbane beetles, among others (Root 1986). The best method to remove the bugs from your milkweed plant is to grab them and throw them into a bucket of soapy water.
They adult is black with a broad orange/red band on forewing, forming an "X" shape. Their head is black with a dull red spot on top. In eastern specimens, forewings are all black, but in western specimens they have large white spots. (Bugguide.net)
Eggs are laid on milkweed in spring. One or more generations per year. Adults overwinter.
Large Milkweed Bug (Oncopeltus fasciatus)
Native range: Throughout North America and from Central America through Mexico and the Caribbean to southern areas in Canada.
Harmful to Monarch caterpillars/eggs? No, they do not feed on Monarch larvae or eggs so they are harmless and play a role in the ecosystem. However, they do feed on the seeds, leaves and stems of milkweeds (Asclepias). Damage to the plants can deplete resources for Monarch caterpillars. Planting more milkweed will ensure that they both have enough to eat.
Identification: Adults are overall black and orange- with black band in the middle and two large black spots in front and back. Nymphs are bright orange and develop black spots late.
Life Cycle: Eggs are laid in milkweed seed pods or in crevices between pods. About 30 eggs are laid a day, and about 2,000 over a female's lifespan, which lasts about a month during the summer. One or more generations per year. They can't survive cold winters, so they migrate south in the fall. They overwinter in the southern Atlantic and Gulf coast states where they feed and breed and gradually migrate north again in the spring and summer. (bugguide.net)
Swamp Milkweed Leaf Beetle (Labidomera clivicollis)
Native range: Widespread in North America east of the Rocky Mountains, south to northern Mexico (Riley et al. 2003)
Harmful to Monarch caterpillars/eggs? Technically, no, because they are herbaceous. However they do feed on milkweeds, especially Swamp Milkweed (Asclepias incarnata), but also Common Milkweed (A. syriaca). To control populations from eating all of your milkweed, you can pick them off and put them in a soapy bucket of water.
Life Cycle: They often overwinter as adults among leaves such as mullein (Verbascum). Adults mate on or around milkweed. Eggs are cemented to the underside of leaves. Larvae feed on leaves, and drop to ground to pupate (National Audubon Society Field Guide to Insects and Spiders)
Note: Unlike the Monarch, larvae and adults of the milkweed leaf beetle are not thought to sequester cardiac glycosides from their milkweed host.
Large Milkweed Bug Profile
Missouri Botanical Garden
Milne, Lorus and Margery. National Audubon Society Field Guide to Insects and Spiders
Red Milkweed Beetle Profile
Small Milkweed Bug Profile