Thursday, August 18, 2016

Insect Teenagers: Milkweed Tussock Moth Caterpillars

Ever since I read of the amazing little ecosystem hosted by milkweeds, I've kept an eye on the plants around my house.  Red milkweed beetles have been pretty common, Monarch butterflies are a rarer visitor, and only once, last summer, was I delighted by finding monarch caterpillars munching away.  (Alas, those few colorful caterpillars were only seen a few times, then disappeared.  I long for the day Monarch caterpillars survive to maturity right here in my city garden, and metamorphose into butterflies to join the great, mysterious monarch migration.)  

 In June, red milkweed beetle will chow down on leaves, but prefers flowers and buds.

 In July they're beginning to develop other ideas--but not all at once. 
"Would you mind?  I'm trying to eat, here!" 

August brings a new member of the community.

Only a week ago I was surprised by a new member of the community: Milkweed Tussock Moth caterpillars.  First there were just one or two, but in a few days there were a dozen or more chomping entire milkweed leaves and dropping big green frass.  Where did they come from?  Gypsy moth caterpillars came and went, their moths also came and went, yet I saw no sign of these guys.  What kind of caterpillar makes its first appearance in August?!

It turns out these caterpillars begin as very inconspicuous things, only developing their full colors late in life.  It's likely the bright colors are a warning to birds, just as for monarch caterpillars: they accumulate in their own bodies the cardiac glycosides milkweed makes as a defense, so the plant's chemical weapon becomes the caterpillar's (and moth's) defense against predators.  I'm guessing their inconspicuousness when young means either they're too small to be a target for birds, or they haven't accumulated enough toxin to be defended by it, or both!

 At this point, they are no longer a rare novelty!  And, like human teenagers,
they're really beginning to make an impact on the larder.

Apparently their parents didn't stick around to teach the youngsters not to poop on their food.

In the space of a few days, these Very Hungry Caterpillars (And, like human teenagers, they really begin making an impact on the larder.) 

 Here is the result of just a few days of non-stop eating.  They plainly don't care for the pods.
And the leaf mid-vein seems to be a little too toxic even for them.

I really don't mind these guys at all.  The milkweeds already have nearly-mature pods--and if they don't mature it'll save me harvesting them all to keep the milkweed population under control!  Of course, assuming the next generation shows up next year, I'll have to keep some milkweed in good shape on the chance my beloved Monarch caterpillars appear!

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