What you find living among your milkweed plants depends on your region. Creatures you might encounter include the following:

Flower crab spiders (Thomisidae) are so named for their resemblance to crabs and their ability to scuttle sideways and backwards. They do not build webs to trap prey, though all of them produce silk for drop lines and reproductive purposes. Most of these tiny spiders are ambush predators, sitting on or beside flowers or fruit, where they grab visiting insects. Individuals of some species are able to change color over a period of days to match the flower on which they are sitting.

Photo: John Flannery by permission

Milkweed bugs (Oncopeltus fasciatus) are colored orange-red and black. Also called seed bugs, they have a long proboscis for piercing and sucking the sap of the milkweed plant and they also feed on the seeds and leaves. The large milkweed bug is found in small groups on milkweed, often on the stems, leaves and on the seed pods. The bodies of milkweed bugs contain toxic compounds derived from the milkweed. Milkweed bugs are true bugs (Hemiptera). They are used as research insects because they are easy to use in the laboratory, have a short life cycle and are easy to manipulate. Milkweed bugs are more of a nuisance than a threat to milkweed plants. They can be found in all stages of growth on the plants to late summer. Milkweed bugs overwinter as adults. Unlike most true bugs that have scent glands, milkweed bugs do not.

Photo: Judy Gallagher, CC BY 2.0

Milkweed leaf beetles (Labidomera clivicollis) browse on the leaves and sometimes on the flowers of milkweeds. Beetles in this family Chrysomelidae number over 1,700 species and subspecies in North America. Milkweed 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, including milkweed.

Photo: David Hill, CC BY 2.0

Milkweed stem weevils (Rhyssomatus lineaticollis) are “short-snouted weevils” in the family Curculionidae. Resembling large-eyed elephants, these beetles appear on common milkweeds before they flower. Females chew a series of holes in the stem and lay their eggs in the holes (this leaves noticeable scars). The weevil larvae develop in the stem, eating the abundant pith material. Like many other beetles, this species "stops and drops" to the ground when startled.

Photo: Arthur V. Evans, D.Sc. by permission 

Milkweed tussock moth larvae (Euchaetes egle) are also found on milkweed. They are also called Harlequin caterpillars because of their showy colors and tufts of hair. Females lay eggs in clusters, and the caterpillars stay in groups during the first part of their larval stage. They may defoliate a plant, but they don’t really compete with monarch caterpillars. Monarchs tend to be found on newer, still-growing vegetation, and Harlequins like older plants. The adults are silvery-white moths with ragged wing edges. 

Photos: (1) CotinisCC BY-SA 2.5; (2) Kevin RipkaCC BY 2.0   

Monarch butterflies (Danaus plexippus) feed as larvae exclusively on milkweed leaves, but the adults nectar from a variety of flowers. There are many generations per year, but those that emerge at the end of summer (called generation 5) migrate south, where all the monarchs east of the Rockies overwinter on the same mountainside in Mexico. The monarchs west of the Rockies overwinter in Northern California. In spring, the same generation that migrated south starts north. They lay eggs as they go and the new generations are the ones that return to their summer grounds. Eggs are laid singly on the undersides of milkweed leaves, and impossibly tiny caterpillars hatch a few days later.

Photo 1 by Flickr user John Flannery under CC BY-ND 2.0photo 2 by Flickr user wplynn under CC BY-ND 2.0 

Queen butterflies (Danaus gillippus) feed as larvae on milkweed leaves. These tropical butterflies are commonly found in Mexico and Central America as well as southern states in North America, where they prefer open woodland, fields, and desert habitats. Like other butterflies, the female queen uses its short forelegs to scratch the surfaces of leaves to determine which ones are suitable hosts for its eggs. Queen butterflies have a wingspan of 3.1 inches (7.9 cm) to 3.3 inches (8.4 cm). As larvae, they are distinguished from monarch larvae by their three pairs of tentacles (monarchs have two pairs). As adults, their wings are browner in color with more white spots than the monarch.

Photo 1 by Wikimedia Commons user Korall under CC BY-SA 3.0photo 2 by Flickr user Renee Grayson under CC BY 2.0

Red milkweed beetles (Tetraopes species) are members of the long-horned beetle family (Cerambicidae), a spectacular group of beetles that can be both colorful and large and that bear long (sometimes very long) antennae. Typically, the adults are plant-eaters (wood, leaves, pollen, flowers) and their grubs feed on wood. This group mainly chows down on common milkweed; its grubs feed on stems and roots of milkweed, and they overwinter within the stem. Their nickname – four-eyed beetle – is the result of the socket of the antennae being located in the center of the eyes, “dividing” them in two. There are 13 species in this genus north of Mexico, each with  different markings.

Photo by Flickr user Yankech gary under CC BY-ND 2.0

Also look for:

  • Queen butterfly (Danaus gilippus) and other milkweed butterflies (Nymphalidae) that use the leaves and flowers as their only larval food source.

  • Various bees, beetles, butterfliesflies, moths, and wasps that use the flowers as a nectar source.

  • Aphids, which pose no threat to butterfly larvae but can look unsightly.

  • Biological pest control insects such as hoverflies, lacewings, ladybugs, and wasps, which can help to control aphids.

Photo via Public Domain