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| Head out of the bag - REK from WOLF |
A
WOLF School
student brought me this bagworm to study. As a child I got a penny for
each bagworm I found on our neighbor's cedars, then used them for
bluegill bait, a sweet deal while it lasted. We find them on our red
cedars which technically aren't cedars but junipers,
Juniperus virginiana.
It turns out these bagworms don't care as they can live on over 50
different tree and shrub species. The females will spend their life in
their bag with only their head and upper thorax ever exposed to
daylight. Talk about a tan line!
This is the common Evergreen Bagworm -
Thyridopteryx ephemeraeformis. Most
of us know them only by their shelters. Back then I would cut them
open to extract the "worm," never appreciating that it might actually be
a gravid mother full of eggs! Legless and grub shaped it wasn't
impressive at all.
Life cycle begins as a wingless, legless and blind
adult female emerges from her pupal case. She will never leave the bag
in which spends the rest of her entire life. She will "call" with her
pheromones and the male will seek her out in her bag. He inserts his
abdomen deep into the sac, fertilizing her without ever seeing his
mate! She immediately starts producing eggs that remain in her pupal
sac (cocoon), sight unseen, where they remain over the winter.
In the spring, newborn larvae 2mm long emerge.
Initially they may feed on their egg cases and other siblings eggs, as
well as the remains of the now dead mother. After 5 days the larvae
leave the case by lowering a strand of silk and "ballooning" in the wind
like baby spiders. They then start feeding on the plants at their
destination, immediately constructing their own bags of silk.
Only
the head and thorax come out of the bag as they move along feeding and
dragging their bags with them as you can see
in this video. They will go through 7 molts in around 4
months. They will continually enlarge their bags using silk and what
ever vegetation they are on, ranging from cedar to sycamores. Finally
they attach the bags to a branch and pupate in it.
When the female emerges from her cocoon, she releases
her "perfume," pheromones specifically tuned to the male's frequency.
The winged male emerges and follows the pheromone scent with his big
feathery antennae ("the better to find you with my dear"). Once he
locates the scent he has to reach inside the bag to fertilize the
female. He lives only a couple of days so time is of the essence. His
abdomen is extendible like a telescope and prehensile, twisting around
to enter inside the bag even though he is facing the other direction.
It moves around quite a bit and tends to extend upward when he is
resting. The abdomen must have some incredible sensors, feeling around
in the dark bag for the female. I am always amazed that this little
moth can find a female hiding in a bag during his brief lifespan. They
must have a good nose (antennae) for it as their numbers attest to their
success.
Pictures of the various instars.
More information is at Beetlesinthebush
and detailed information is in this Smithsonian Institute paper.
