I
f you pay attention to milkweed plants during the summer,
you'll notice a wide variety of insect species feeding on the
nectar produced by milkweed flowers. That nectar is sweet,
nutritious and free of the toxic latex found throughout most
of the rest of the plant. A much smaller group of insects
can be found feeding on the leaves, stems or seeds of those
milkweed plants, both dealing with and taking advantage
of the toxicity. Those insects include monarch caterpillars,
milkweed tussock caterpillars, oleander aphids, longhorned
milkweed beetles and both large and small milkweed bugs.
All of those insects have compelling natural history
stories, but this article focuses on the large milkweed bug,
an insect that is commonly seen, but often misidentified.
The uncreatively-named 'large milkweed bug' (Oncopletus
fasciatus) is different from two species of 'small milkweed
bugs' (Lygaeus sp), and those are different from boxelder
bugs (Boisea trivittata). It's easy to confuse them with each
other, speaking from personal experience, but
a few simple visual cues can help you tell
them apart.
First, boxelder bugs are much
more black than orange when
viewed from the top. The orange
is mostly an accent color on an
otherwise black back. In comparison,
both the large milkweed bug and the various species of
small milkweed bugs have considerable orange coloration.
The large milkweed bug has a longer, more slender body
shape and a solid black band across the middle of its back.
That contrasts with the black hourglass shape and solid
orange 'X' on the back of small milkweed bugs. Got it? This
article focuses on the large milkweed bug — the one with the
slender body and a black band across the back.
Large milkweed bugs are specialist herbivores on
milkweed plants, especially common milkweed (Asclepias
syriaca). Milkweed plants produce latex, which is the white
Large
Milkweed
Bugs
38 Nebraskaland • August-September 2020
Story and photos by Chris Helzer
BOXELDER BUG
