Monday, August 29, 2011

Cecropia Caterpillars Make Silk Cacoons

 The Cecropia moth caterpillars at Springbrook have become almost groteskly huge and fat.  All they do is eat day and night until they can barely waddle to a new leaf.
Of course they need to eat now to have enough fat to overwinter in their cacoons and have the resources to emerge next spring as one of Minnesota's largest and most beautiful moths.

But since late May they have been eating machines.

Take a look below at the huge green eyes and the mouth on this caterpillar.  It has a transparent upper lip! And pretty weird "teeth" below.  I took these pictures in the last few days as I waited to photograph the caterpillars as they transformed into cacoon makers. Scrool down to see the action.

After finally eating all they can hold, the caterpillars sit still for several hours, seemingly transforming their mouth from leaf eating to silk making.
This moth is a member of the Saturnid moth group that includes the caterpillars that silk cloth comes from. 

Notice the light blue "spiracles" on each segment of the caterpillar.  These are the breathing holes that allow insects to breathe.  Also notice the three little "true" legs near the head.  Three more on the other side account for its six true legs.  The large projections from its abdoman that look like legs are called pseudo or false legs.  These "legs" will now dissappear for the rest of this insect's life.

You can see in the picture below how the caterpillar begins to have a glistening silk thread emerge from its mouth, wrapping it all around itself and the branch it is on.  Meanwhile its body seems to begin turning white.  The silk is sticky when it first comes out but hardens to one of the strongest tensile strength "lines" known on earth. 

It takes the caterpillar about 12 hours to get a good start on the cacoon. In another 12 hours it is completely covered but can still be seen, as you can see below.  At this time the silk is white, which is the color that the silk stays with real silk worms.  Their cacoons are unwound into one long silk thread and then woven into wonderful silk cloth.

But with the wild "silk" moths, the Polyphemus, the Cecropia, and the Luna, here in Minnesota, the "silk" turns brown after another day, as this one was doing yesterday.  Some of it is still white but will turn brown within a day.
The caterpillar will continue inside to make a thick wall of silk, and after several days will stop, and in a couple of weeks it will turn into the pupae and wait for the warmth of next May and June to emerge as the adult moth.  I'll post more pictures then of the moth.

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