Arb Sightings 8/11/04

Posted on August 11th, 2010 by

At last, the end to these unbearably hot and humid days is near. Another day above 90 degrees Fahrenheit tomorrow should give way to cooler temperatures arriving on Friday and Saturday, and by Sunday our highs should once again be in the comfortable 70’s. While we could use some more precipitation, we’ll have to be content with the 0.47 inches of rain that fell in St. Peter over the past seven days (other nearby locations received over an inch, however), as the approaching cooler air looks to be fairly dry as well.

The Bird and Butterfly Garden continues to amaze and delight its human visitors. Monarchs, Red Admirals, and Painted Ladies are in the majority this week, but the highlight for most has been the discovery of two monarch chrysalids. A chrysalis is somewhat like a cocoon in that it is the pupa stage of the butterfly, or the stage in which it transitions from larva to adult; but while a cocoon is formed from the silks woven by many moth caterpillars, the chrysalis of a butterfly is formed from the caterpillar’s hardened skin. The monarch chrysalis is green rather than the contrasting striped coloration of the caterpillar so that it may be camouflaged from predators if attached to a plant, and the monarch will stay encased in this pupa for anywhere between ten to fifteen days before emerging as an adult butterfly. And the caterpillars rarely make their chrysalids on milkweeds; instead they usually find a nearby well-sheltered location away from disturbances.

Below is a photo of one of the chrysalids attached to the underside of the Interpretive Center’s roof edge.

Monarch chrysalis attached to underside of Interpretive Center's roof edge, 8/10/10.

The following photo is of one of the caterpillars in its characteristic pre-chrysalis “J” form (which became a hardened chrysalis about an hour after the photo was taken this morning) attached to the rock wall lining the Bird and Butterfly Garden. Note the green coloration beginning to appear near the caterpillar’s head.

Monarch caterpillar in pre-chrysalis "J" form attached to rock wall lining Bird and Butterfly Garden behind Interpretive Center, 8/11/10.

What’s perhaps even more noteworthy is that when these two monarchs emerge, their generation of adults will most likely be the first fall migrants that fly south all the way to the overwintering sites in the mountain ranges northwest of Mexico City. Studies suggest that monarch adults emerging from their chrysalids in southern Minnesota after August 15 are migratory, while the adults that emerge prior to that date still belong to the non-migratory summer populations (whose offspring will also become migratory once they emerge as adults in September).


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