Naturespeak A naturalist's view of the world

June 28, 2008

Stepp’n Out and Stink’n Up

Filed under: Uncategorized — wykes @ 8:35 pm

  In nature study, plant watching and butterfly watching are one in the same. Insects of the scaly winged clan are life-bound to particular plant families as their larval food.  It is almost as if they signed an exclusive contract back in the dim times in order to guarantee the mutual survival of both. This contract is honored to this day. This means that if you locate a particular type of plant you will have a good chance of locating a particular type of larval butterfly.

  The association between Monarch and Milkweed is a well known example of this principle. I’ve previously mentioned the Painted Lady / Pussy Toe connection and many gardeners are all too familiar with the Cabbage White/ Cabbage connection. The Black Swallowtail/ Parsley bond is less familiar, but is as sure-fire as these better known combinations.

  Black Swallowtail butterflies lay their eggs on members of the parsley family such as Wild Carrot, Parsley, Dill, and Cow Parsley. Cow Parsley is a weed plant that has proven to be trouble for some members of the human clan – it has been known to cause rashes – but it can serve as a swallowtail magnet. A recent examination of a Cow Parsley specimen revealed a bunch of the multiply striped larvae feasting on the leaves. The little creatures were in all stages of growth from newly hatched to late stage “mature” larvae (like individual shown above).

  When they first hatch, they have white saddles on their dark little wrinkled bodies. This combination gives the tiny larvae the appearance of bird poop. Based on the solid ecological knowledge that birds don’t eat their own poo, being a poo mimic can keep you living into the next stage.  

  Caterpillars go through a series of growth spurts called instars. They advance to the next stage by shedding their old skins. The first few instars are crappy in nature (see here one that still has the white saddle). After a week or so, the young are ready to come into their own. 

  I located one individual that had just walked out of his old poo-mimic skin as a late stage caterpillar. Take a look here and you can see the old shriveled skin adhering to the stem behind it. In preparation for this action, the larva wove a silk pad and firmly sunk its tiny claws firmly into the weave. Once so secured, the skin then split along the back and the beastlet literally crawled out of its own skin.

  The “mature” Black Swallowtail caterpillar is a handsome looking thing. It seems funny to say that a caterpillar is “mature” – since the creature is technically still a baby.  The late stage is the “big baby stage” at the end of youthdom. The rich pattern of black & yellow against that glowing green backdrop is a definite “I am not crap” fashion statement.

  Now that the larva is not protected by the cloak of mimicry it has to fall back on another ingenious defense tactic. Should a predator get a beak hold on one, it will let loose with an organ known as a stinkhorn (see here). This bright orange horn emerges out of a pocket just behind the head capsule. Its appearance is shocking enough, but the effect is accentuated by a backward jerk of the head.

  The horn exudes a strongly scented concoction distilled from a concentration of parsley chemicals. By reeling back and swaying the caterpillar attempts to smear the liquid onto its attacker. This brew must be offensive to fur and feather predators, but I don’t think it smells all that bad. It merely stinks of over ripe vegetable juice in my humble opinion.

  I let the larvae apply a liberal dose on my fingers as I attempted to get a decent photo. It took the better part of a day for the smell to go away and this provided me an opportunity to invite a few folks to take a whiff. I didn’t ask them to pull my finger, mind you, just to sniff it.


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