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.

Sunday, August 21, 2011


 The annual cicadas are out and announcing their presence with their high pitched buzzing call.  They are usually high up in the trees but they live short lives as adults and soon drop onto driveways or decks and become food for other creatures.  This one was alive but lying on my driveway this morning.

Some cicada species live underground for many years.  13 years is one, along with the well known 17 year cicada.  But our common cicada is only underground one year.

Cicadas are in the group of insects called Hemiptera, or True Bugs.  This group of insects all have straw-like sucking mouth parts and most use their "straw" to pierce plant tissue and suck out nourishment from the plant.  After mating, female cicadas lay eggs in the stems of tree branches.  The hatchlings drop to the ground and burrow down to one of the tree's roots.  They attach their straw like mouth to the root and stay attached for the next year, growing as the tree feeds them. 

After their year in the ground the larvae crawl out on a late summer night and climb a few feet up the trunk of the tree.  In the picture below you can see the shell left after they emerge from the ground with the dirt still attached.

 Most everybody has found these left over "skins" of a larvae cicada attached near the bottom of a tree with the obvious split in the back where the adult emerged and crawled up the tree to let its wings dry and expand. I found this empty shell on the tree near my driveway where I found the adult cicada. The adult then flies into the branches and seeks a mate.
This is the male cicada that I found.  You can see the slender tube like sucking mouth part sticking down beneath its front legs.

Cicadas are very heavy bodied insects and not very good fliers.

The females listen for the "singing" males, and pick one out that sounds perfect to her.  She then flies to the tree and locates the male by his buzzing call.  After introductions, if all goes well, they mate and the female then finds an appropriate branch to lay her eggs in. 
The male makes his buzzing call by slapping or clapping two pair of plate like body peices together.  Here you can see one pair just below the hind leg and to the left of the green wing edge.  One lays ontop of the other.  As he snaps the top plate down onto the other it makes a snapping sound.  When he does this very fast with both pair of double "plates" the loud high pitched buzzing sound is the result.

Hearing the cicadas always means the peak of summer is past, and I'd better enjoy what is left.

Thursday, August 11, 2011

Deer Fawns

Springbrook's white tail deer fawns are growing up, but they will keep their spots for several more weeks to help hide them in the dappled sunlight of their forest habitat. 

They are very curious, but still never get very far from mom, as you can see in the bottom photo.  I took these pictures today by Springbrook's feeders

The fawns watch their mom closely, and learn when to be cautious and when it is ok to play.