It’s a long time from late January to late May. The days are getting longer and we might see some different behavior with birds and squirrels at the feeders. Canine breeding season is beginning to happen in the region and baby bears are born about this time. But we still have weeks of cold and snow ahead of us as we move in that direction.
However, there are several nature happenings now that are preparing for spring. Most obvious are buds on local deciduous trees. Within the small scaly coverings out on the twig are the new leaves, already green.
Also of note are seeds of many roadside plants: tansy, sweetclover and mullein, just to name a few. This cold time with less light is important for their growth. Opening buds and seeds too soon could make problems for the plants.
Another example of a preparation for the spring time was made apparent to me when I was shown a large cocoon that was recently discovered. It was attached to the stem of an alder growing near a swamp. Exposed to the cold without any apparent heat, the resident inside was alive and getting ready for its next phase of life.
Cocoons are made by moths, who use silk and leaves to fold over their pupated body. (Butterflies form a chrysalis from their skin.) We all are familiar with the moth metamorphosis: A caterpillar (larva) goes into the cocoon and comes out as an adult, looking quite different. (It is interesting to note that we might know moths better as caterpillars, such as woollybears or armyworms, than we do as adults, but with butterflies, it is the opposite.)
Though we see the beginning and the end, we mostly don’t know what happens to make these changes within the cocoon. Often referred to as a resting stage, the first weeks inside the cocoon are not resting.
The caterpillar does dramatic altering to become a moth. The body of the caterpillar is essentially digested from the inside. Once secure in the shelter of the cocoon, hormones trigger enzymes to do the digestive changes.
- Northland Nature: Watching cold-weather moths
- Northland Nature: Brown ringlets flutter on flowers
- Northland Nature: Lunas fly under June moon
Organs used by the caterpillar are reduced and replaced by others. Cells known as imaginal discs form to produce completely new body parts that the caterpillar did not have. Antennae, eyes, wings, legs and related muscles need to develop. Adult moths will lay eggs and so reproductive organs are formed. And since many adults do not feed, their digestive system is altered as well. (Caterpillars seem to eat all the time.)
What begins as a “worm” becomes a winged insect within the cocoon. The development is then followed by a period of dormancy in cold temperatures so adults do not emerge too early. They need to be in synchrony with the spring season.
Cocoons vary with different species. The cocoon that I was shown was of a large moth: the cecropia. If we are fortunate to see this magnificent moth of a reddish-brown color and a wingspan of about 5 inches, it would be in late May or early June. As adults, they do not eat and so flight time is short. They seek a mate and lay eggs.
Their caterpillars of summer change from dark color to green over a period of five molts, growing to about 4 inches long. Cocoons are formed in fall. If we see them in winter, it is best to leave them. They need to experience cold to complete the development from caterpillar to moth.