I Speak for the Milkweed Tussock Moth!

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I came across early instar milkweed tussock moth caterpillars (Euchaetes egle) feeding on their namesake host yesterday and they reminded me of an e-mail message I received last year.  The message was from a well-meaning monarch butterfly (Danaus plexippus) enthusiast who asked how they could control tussock caterpillars so they wouldn't compete with monarchs.  I was aghast.  We celebrate the rejection of a monarchy each July 4! 

 

It can't be denied that milkweed tussock moth caterpillars are ravenous feeders and serious competitors to monarchs.  All instars feed side-by-side in groups and a single colony can rapidly consume entire leaves leaving only the veins.  In fact, high populations can out-devour even the most voracious monarch caterpillar.  However, the tussock moths are also native insects; they should enjoy the same natural born rights to milkweeds as monarchs.  I support the colonies!

 

Milkweed Tussock Moth Caterpillar Damage

 

Milkweed Tussock Moth Caterpillar Damage

 

I'm also partial to the ugly duckling story played out as the tussock moth caterpillars develop.  Most pictures posted online show the colorful late instar caterpillars such as the one appearing at the beginning of this report.  The black and orange hairs punctuated by tufts of long white and black hairs are responsible for the alternate common name of "milkweed tiger moth."  Early instar caterpillars represent an ugly duckling stage.  The small, yellow-green caterpillars have no discernable markings.  With black head capsules and wispy white hairs, they have been described as "non-descript;" an ignoble label.

 

Milkweed Tussock Moth Caterpillars

 

Milkweed Tussock Moth Caterpillars

 

The colorful late instar milkweed tussock moth caterpillars are actually advertising their chemical defense strategy.  Like monarch caterpillars and many other milkweed-herbivorous insects, the tussock moth caterpillars dodge predation by accumulating in their flesh the alkaloid toxins, called cardiac glycosides (cardenolides), which are concentrated in the milkweed's sap.  As with other insects that feed on milkweeds, including monarchs, late instar tussock moth caterpillars advertise their toxic character through splashy coloration; a twist to the old axiom that "you are what you eat."

 

Of course, I support monarch recovery.  However, we should embrace all native insects with equal affection; I mean this figuratively since tussock moth caterpillars also have defensive hairs.

 

In summary, I quote Groucho Marx:  "Those are my principles, and if you don't like them... well, I have others."

 

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