Bug Stories

An adult Large Milkweed Bug (Onopeltus fasiciatus) on
Tropical Milkweed (Asclepias curassavica) 

Two brightly colored species of bugs are conspicuous in the fall and they are not even trying to hide.  They are the Large Milkweed Bug (Oncopeltus fasiciatus) and the Boxelder Bug (Boisea trivittata).  These two are true bugs in the Order Hemiptera, a group that also contains aphids, leafhoppers and stinkbugs. Hemiptera go through incomplete metamorphosis.  When a true bug hatches, it enters a larval stage called a nymph.  Nymphs look like miniature adults but lack wings.  The nymphs eat and grow.  As they grow, the nymphs molt their exoskeletons several times. With each molt they becomes larger nymphs. After going through several nymphal stages, they undergo a final molt to make the winged adult.  This type of development contrasts with complete metamorphosis where a worm-like larva emerges from the egg.  After several molts, the larva makes a cocoon or chrysalis where a complete rearrangement of the body plan produces the adult.  Moths and butterflies are typical insects with complete metamorphosis.  The larvae are the caterpillars and the adults are flyers.     

Large Milkweed Bugs spend much of their life on milkweeds (Asclepias sp).  Like Monarch Butterfly larvae, Large Milkweed Bugs consume their host milkweed and incorporate cardiac glycoside toxins into their bodies. Like Monarch Butterflies, Large Milkweed Bugs have a bold pattern of orange and black to warn predators.  

Large Milkweed Bugs on a fruit of Asclepias sp.

Large Milkweed Bugs have four nymph stages and at each stage, the nymphs are bright orange.  The adults have wings that are black with an orange “X” pattern.  Both nymph and adult Large Milkweed Bugs use a mouthpart called the proboscis to suck nutrients from their host milkweed plant.  Adult Large Milkweed Bugs survive the winter in this area by burrowing in leaf litter and entering a hibernation-like state called diapause. 

Large Milkweed Bugs mating on a Milkweed

Eggs of Large Milkweed Bugs on the underside
of a Tropical Milkweed leaf. 

A mixed group of adult and nymph Large Milkweed Bugs on the leaf of
Common Milkweed (Asclepias syriaca). The large nymphs have small, black,
non-functional wings.  

Large Milkweed Bugs nymphs feeding on seeds of Common Milkweed. 

It is no surprise that Boxelder Bugs live on Boxelder trees (Acer negundo).  Boxelders are not elders at all, they are maples.  Boxelders are interesting for a couple of reasons.  First, they are the only North American maple with compound leaves.  Boxelder leaves typically have 3-7 leaflets.  Second, Boxelder is the only North American maple with separate male and female trees.

A single compound leaf with three leaflets
of Boxelder (Acer negundo).

Winged fruits with seeds of Boxelder.

Boxelder Bugs have a wider range of hosts than the milkweed bugs, laying their eggs on Boxelder, other species of maple and ash trees.  The eggs hatch and bright orange nymphs emerge.  The nymphs feed on their host plant, particularly the seeds, grow and molt.  Like the Large Milkweed Bug, Boxelder Bugs have four nymphal stages and then molt into the winged adult. 

Boxelder Bug nymphs (Boisea trivittata) on the bark of
a Boxelder tree (Acer negundo).  The large nymphs have
non-functional wings. 

A group of Boxelder Bugs with both adults and nymphs. Adult
Boxelder Bugs have dark brown wings with orange stripes.

Adult and nymph Boxelder Bugs.

The adult Boxelder Bugs are dark brown to black with deep orange stripes on the wings.  The colors are warning signals to predators not to eat these bugs.  Indeed, Boxelder Bugs are protected by chemical defenses.  Unlike Large Milkweed Bugs and Monarch Butterflies, Boxelder Bugs do not ingest toxic chemicals from their host plants but make them from scratch.  Boxelder Bugs have glands in their abdomen that release noxious smelling (and tasting) compounds if attacked by a predator.  Because the nymphs feed on the Boxelder seeds large groups of Boxelder Bugs of different developmental stages are found on the female Boxelder trees during the fall.     

Boxelder Bug nymph feeding on a Boxelder seed.

Be on the lookout for these bright bugs as the bug season winds down.