Tuesday, August 31, 2010

One cool cat

Our butterflies fall into two groups: butterflies (duh!) and skippers. The former includes all of the big, showy and easily recognizable species such as the Monarch, various swallowtails, sulphurs, Red-spotted Purple, etc.

It's the skippers that tend to vex people setting out to learn our lepidopterans. Skippers are small and often inconspicuously brown, often behave more mothlike than butterflylike, and the species can be confusingly similar.

Not so the bold and pugnacious Silver-spotted Skipper, seen above nectaring on Swamp Thistle, Cirsium muticum. A jumbo in the world of skippers, the flashy Silver-spot is probably the first skipper many people learn, and the most widely recognized of its ilk.

Well, the Silver-spotted Skipper and every other butterfly and moth was a caterpillar before they transformed into the beautiful and much more obvious flying machines that we see flitting about. Voracious plant-eating machines, these cats are adept at hiding and not often seen. It behooves these tasty little bags of protein to remain in hiding during the day, when birds and all manner of other predators who would love to make a snack of them are out and about.

But, the trained eye can still find caterpillars. In the case of the Silver-spotted Skipper, watch the foliage of its favorite host plant in these parts, the Black Locust, Robinia pseudoacacia. Should you see a series of leaflets pulled over and sewn together with silk, you're liable to have an SS Skipper larva.

And what a caterpillar! Carefully unfurling the leaves exposes an utterly alien-looking beast; like something straight off the space craft. I suppose there might be a shock value to those large orange "eyes". If some bad guy got to poking around and uncovered a Silver-spotted Skipper caterpillar, and that fake head lunged in its direction, it might be enough to send the potential predator packing.

The thumb provides a size perspective to this last instar skipper larva.

Here's one reason that caterpillars have evolved such good hiding techniques and camouflage. This, I believe, was a Pawpaw Sphinx caterpillar, which is a much larger animal than the Silver-spotted Skipper cat. Lots of things love to take advantage of large meaty caterpillars, either for a quick gulp of a meal or as a provision to feed their offspring.

The little oblong white cases are the coccoons of a braconid wasp, which are common parasitoids of caterpillars. If the adult wasps locate a suitable caterpillar, they'll either lay their eggs on the unwilling host or inject them into its tissue. When the eggs hatch, the tiny wasp grubs burrow happily through the caterpillar's tissue, consuming all of the non-vital stuff. Finally, in a last hurrah, the grubs finish off the victim in a fatal feeding frenzy and burst from the victim to pupate, as seen above.

With threats like that lurking around every leaf, I'd hide too.



Scott said...

Great post, I've spent a bunch of time hunting for one of these caterpillars without success. They are either not in my locust trees or the are up high in the tree. Given the large numbers of adults I have in my yard I suspect the latter.

Jim McCormac said...

Thanks, Scott. Keep checking - there must be some there!


pambirds said...

Sheesh, that wasp is one nasty egg-laying critter!

Rodney said...

Thanks for the great information! The kids and I discovered one of these caterpillars today, and promptly looked its identity up when we got home. Your site was a great resource for us.

Butterfly Lover said...

Thanks for sharing your blog... I'm a critter catcher too, specifically leps. You can see my butterfly, moth, blog here... http://fortheloveofbutterflies.blogspot.com/
Again, thank you. I look forward to learning from your blog.