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MILKWEED BUGS
Milkweed bugs are true bugs; beetles, moths, flies, and butterflies
are not. Bugs have the usual complement of structures that they
share with just about all other insects: six legs, three body
parts (head, thorax, and abdomen), and two antennae. True bugs
(order Hemiptera) do not have mouths for biting and chewing food—they
have a tubelike beak for sucking fluids. The milkweed bug in nature
sucks nutrients from milkweed seeds, but those in the classroom
have been bred to feed exclusively on sunflower seeds.
Another characteristic of bugs generally and milkweed bugs specifically
is the stages they go through from hatching to maturity. Bugs
go through simple metamorphosis. The insect emerges from an egg
looking like a tiny version of the adult, with slight differences
in body proportions and incompletely developed wings. The immature
bugs are called nymphs. Newly hatched nymphs are analogous to
the larvae of insects that go through complete metamorphosis,
in that their prime directive is to eat and grow. As with all
insects, in order to grow the nymphs must molt periodically. Just
after molting the bug is creamy yellow with bright red legs and
antennae. Within a few hours the body turns dark orange, and the
legs and antennae resume their usual black color. The crispy little
molts can be seen in the milkweed bug habitat about a week after
the bugs hatch. Students may think their milkweed bugs are dying
or that spiders and ants have invaded the habitat. It may take
a while for students to figure out what the molts really are.
Life cycle. Milkweed bugs advance through five
nymphal stages (instars) as they mature. Each molt produces a
larger nymph that is more completely developed. As the bugs grow,
the dark wings appear on the backs of the bugs as black spots.
Other black markings start to appear and eventually develop into
the characteristic patterns of black and orange by which the adults
of the two sexes can be identified. The last molt reveals the
adult. There is no pupal resting stage as in insects that undergo
complete metamorphosis—the large nymph simply molts, and
away walks the adult.
Milkweed bugs continue to feed as adults, inserting their long
beaks into sunflower seeds to suck out oils and other nutrients.
Mating is easily observed, as the two mating bugs remain attached
end to end for an extended time. It is possible to distinguish
female and male adults by body markings. Look on the ventral (belly)
side of the bugs. The tip of the abdomen is black, followed by
a solid orange segment (with tiny black dots at the edges). If
the next two segments following the orange band have solid black
bands, the bug is a male. However, if the segment following the
orange band is orange in the middle, making it look like it has
two large black spots on the sides, followed by a segment with
a solid black band, the bug is female. (See the Milkweed Bug Male
and Female poster.) Males tend to be smaller than females. Look
for mating bugs to identify males and females—there will
always be one of each in such pairings.
Several days to 2 weeks after mating, the female lays a cluster
of 50 or more yellow eggs (which turn orange fairly quickly) in
a wad of cotton. The eggs can be removed to a new culture container
or left in the habitat to continue the life cycle.
Milkweed bug habitat. Culturing milkweed bugs
is fairly easy. The bugs require no soil or green plant material.
Just about any container is suitable for a habitat. Because milkweed
bugs can walk on any surface, including smooth plastic, glass,
metal, wet surfaces, and all textured surfaces, the habitat must
be closed tightly, and the ventilation holes must be tiny so the
first instar nymphs can't escape.
We suggest a plastic zip bag for the habitat container. Use a
pin to poke a hundred holes in the bag, and install a water container
in the bottom. To add interest, put a branch in the bag and attach
a bundle of raw, shelled sunflower seeds and a cotton ball to
the branch. Hang the bag from a paper clip next to a wall out
of direct sunlight.
Maintenance. Maintenance is minimal. Keep an
eye on the water level, and when it gets low after 3–4 weeks,
add water and perhaps replace the wick. A new bundle of 20 to
30 sunflower seeds each month should be adequate for a modest
culture of 25 bugs. The culture may start to look a little messy
after a month as little brown spots of waste appear on the walls
of the bag and the molts start to accumulate. Transfer the branch,
water fountain, and bugs to a new bag to renew the aesthetic appeal
of the culture.
Ordering milkweed bug eggs. Milkweed bug eggs
must be ordered from a biological supply company. Specify at the
time of order when you want the eggs delivered. See the Materials
folio for more information about obtaining insects. Conduct Part
1 as soon as the eggs arrive—they will hatch in a week or
less after you receive them. Color is an indicator of maturity.
If the eggs are pale to school-bus yellow, it will be a few days
until they hatch. If the eggs are pumpkin-orange to red, they
will hatch in the next couple of days.
What to do when they arrive.
- Eggs are shipped on a wad of floss. If you
are unable to begin the investigation when the eggs arrive,
they may be kept in the container at cool room temperatures
or refrigerated for short periods; otherwise they will hatch
within one week. If the eggs have hatched upon arrival, add
a few sunflower seeds and hatched nymphs to the vials for distribution
to the students.
- Keep adult males and females in separate
containers. A 1/2-liter container with small air holes can be
used for a few days. Add a few sunflower seeds and a moist paper
towel wick for moisture. To keep adult milkweed bugs for a longer
period of time, place in milkweed bug habitats with sunflower
seed packets, water fountain, twigs, and floss for eggs.
End the life cycle. As long as the four needs
are attended to, new generations of milkweed bugs will continue
to flourish in the habitat. At some point you may want to end
the cycle. Although the bugs would probably soon perish if released
into the environment, it is not suggested that you do so, as they
were not originally from the environment. Place the bag in the
freezer overnight to kill the bugs; discard the bag in the trash.
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