12 Summer 2017 Applegater
The California Tortoiseshell
butterfly in flight this summer
BY LINDA KAPPEN
As with most species,
the male perches looking
for females. The females
will lay their eggs in
bunches on the host
plants. As the young
caterpillar grows, it
feeds on the leaves in a
close group with other
caterpillars.
Adults overwinter
and will fly early in the
day, coming out on
California Tortoiseshell butterfly warm days through late
winter and spring. In
The California Tortoiseshell (Nymphalis mid-spring, the Tortoiseshells mate and
californica) is of the Nymphalidae family of lay eggs for another brood. In southern
butterflies. It is dark brown with a reddish- Oregon, these butterflies may have up to
orange tinge and big and small black spots two or three broods some years.
The overwintering adults feed on fir-
on the middle of the upper side. A dark
brown to greyish pattern, which resembles needle exudate in early spring. Exudate is
a dead leaf or tree bark, appears on the a substance excreted by fir needles. Adults
underside of the wings. The butterfly’s will later use nectar for food and visit
mud puddles or damp spots in roadways.
wingspread can be up to 2.5 inches.
Notes from a Rogue entomologist
Insects on milkweed—
more than just monarchs
BY RICHARD J. HILTON
Monarch butterflies are always a
welcome sight, and finding caterpillars
with their bright yellow and black bands
feeding on a milkweed plant is inevitably a
delight. Add in a chrysalis that is adorned
with gold trim and it is easy to see why
such a spectacular species is the focus of
so much attention.
The fact that monarch butterflies engage
in an annual migration covering thousands
of miles is remarkable. Unfortunately,
the overwintering sites in Mexico for the
population of monarchs that migrate
into the Eastern and Great Plains states
have been under threat, and while they
are now largely protected, climate change
and habitat destruction loom as very real
concerns for this charismatic species.
Our western monarchs overwinter
in California and while the threat there
is not as severe, the western population
has declined over the last 20 years. In
response to the reduced numbers of
monarchs, there has been a nationwide
effort to plant milkweed and monarch
waystations to encourage them in their
migration. Milkweed plants contain toxic
chemicals that the monarch sequesters and
uses to deter predators, accounting for its
dramatic coloration that acts as a warning
sign to potential predators.
However, monarchs are not the only
insects that can live on milkweed and
survive the toxins produced by the plant.
Locally, there are three insect species
other than monarchs that you will often
find when you are out searching milkweed
plants for monarch caterpillars. The
oleander aphid is probably the most
commonly seen. The oleander plant is
in the same botanic family as milkweed
and also produces some similar toxins.
The oleander aphid is bright yellow with
dark legs, feeds on the plant sap with a
sucking mouthpart, and can reproduce
rapidly. You often find milkweed plants
whose pods are completely covered with
these small insects. Gardeners growing
milkweed often consider these aphids a
pest and unwanted competition for the
desired monarchs. Look for articles on the
web, like the one titled “10 Good Ideas
for Keeping Milkweed Aphid-free…and 1
Bad One” at monarchbutterflygarden.net/
control-aphids-milkweed-plants.
Another milkweed-sucking insect is the
small milkweed bug, which is extremely
common in our region. (There is also a
large milkweed bug that has distinct red
coloration and, while it is reported to be
in Oregon, I have never observed it here in
the Rogue Valley.) The small milkweed bug
is often confused with the boxelder bug as
they are both “true bugs” and have a similar
size and shape. In addition, both insects
have some orange to red coloration. You
can tell the difference—the small milkweed
bug’s markings are more pronounced,
making an X shape on the insect’s back,
and the small milkweed bug can also have
two white spots towards the rear end.
The last of my trio of local milkweed
insects other than monarchs does not
have any yellow, orange, or red warning
coloration, but it is, to my mind, the
most striking of the bunch. It is popularly
known as the cobalt (or blue) milkweed
beetle. This metallic-blue beetle is found in
population. They hibernate, reproduce,
and live here throughout the summer.
In fall they will overwinter here again
with some emigrating south to live.
There is still much to learn about
the reasons for the large irruptions
of the California Tortoiseshell. One
reason may be the health and optimal
conditions for specific predators of the
butterfly, e.g., a parasitic wasp. Thus a
good year for parasitic survival results
in lower numbers for the butterfly, and
vice versa.
Tortoiseshell underside
The last large population irruption
of this butterfly that I witnessed locally
They can be seen in flight from January to was around 2001, when hundreds of
November. April through August are peak California Tortoiseshells flew around
Applegate School and were seen in large
months for this butterfly.
Host plants are species of Ceanothus groups puddling on the track, which is
(wild lilac). Breeding occurs in the decomposed granite. There may have
Ceanothus zones of the mountains. been a smaller irruption in 2009 in our
This butterfly lives in lower elevations mountains, including the Cascades. After
in clearings and at edges of forests and witnessing an irruption, folks sometimes
in woodlands, canyons, river corridors, mistake the butterflies for migrating
and brushy areas. They have a wide range Monarchs, only to find out they are indeed
on the western side of the Rockies from California Tortoiseshells. It would be
British Columbia, on the Pacific Coast, to awesome to witness another irruption of
Baja, and east to Colorado, New Mexico, this beautiful insect!
Linda Kappen
Montana, and Wyoming.
humbugkapps@hotmail.com
The California Tortoiseshell is known
Butterfly photos by Linda Kappen.
to have irruptions or “outbursts” in
the western US and is fair-
sized (between a quarter-
inch and a half-inch long).
Occasionally you can find
quite large populations
feeding on milkweeds, and
when that happens they are
hard to miss.
Both the cobalt
beetle and the monarch
have evolved the same
physiological mechanism
for dealing with the toxin
produced by the milkweed
plant. Additionally, the
adult cobalt beetle and the
final stage of the monarch
caterpillar have also developed
an interesting adaptive
behavior whereby the insect
cuts the stem or mid-vein of
the leaf prior to feeding on it.
This reduces the sap flow and
lessens the amount of toxins
moving into the leaf that is
being consumed.
The monarch butterfly is
one of our most recognizable
insect species, but this summer
when you see a milkweed
plant, please keep an eye out
for some of the lesser-known
insect inhabitants that can
survive on this poisonous host.
One of the pleasures
of studying insects is their
immense diversity, and the
group of insect species that
can thrive on milkweed plants
is no exception.
Richard J. Hilton
541-772-5165 ext. 227
Senior Faculty Research
Assistant / Entomologist
Oregon State University-
Southern Oregon Research
and Extension Center
richard.hilton@oregonstate.edu
Top photo: Oleander aphids (wildernesscenter.org).
Middle photo: Small milkweed bug
(commons.wikimedia.org).
Bottom photo: Cobalt milkweed beetle (thoughtco.com).