Thursday, September 8, 2016

Bagged Worms

WOLF student's bagworm - REK

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.

OSU.edu
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.

Adult male - Andy Reago & Chrissy McClarren
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 while going 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. 

  Ted C. McRae
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.

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