Friday, February 25, 2011

Where do they go in the winter?

Ever wonder where all the butterflies and moths go during the winter? For insects, as well as some other animals, this period of winter dormancy is referred to as diapause, as opposed to true hibernation.  The term hibernation is often used to describe overwintering in general, but the specific definition is for an animal that builds up lots of body fat to sustain it during the winter, and experiences a significantly decreased heart rate and body temperature during the dormant period.  Diapause is a delay in development, and is the result of very specific stimuli. Wikipedia has a thorough description of diapause if you care to learn more.
Depending on the species, butterflies and moths overwinter in either the egg, larva, pupa, or adult stage.  Skippers (family Hesperiidae) generally overwinter as either a larva or pupa.  Most swallowtails (Papilionidae) overwinter as a pupa.  Whites and sulphurs (Pieridae) generally overwinter as larvae or pupae, except for the pine white (Neophasia menapia) which overwinters in the egg stage. Most coppers and some hairstreaks (part of Lycaenidae) overwinter as eggs, while other hairstreaks and most blues (also Lycaenidae) overwinter as larvae or pupae.  Species in the Nymphalidae family greatly vary, with the fritillary and checkerspot species generally overwintering as larvae, tortoiseshells and anglewings as adults, and wood nymphs and arctics as larvae or pupae.  These variations in overwintering stages factor into the emergence times of the adults, since species that overwinter as pupae or adults are usually the first butterflies and moths seen in the spring, while the overwintering larvae and eggs must finish their development before emerging as the more visible adult stage.
Have you wondered why the familiar woolly bear caterpillars always seem to be everywhere in September and October, but you never see them when they are smaller?  That is because the caterpillars feed on alder and other broadleaf trees where one normally wouldn't notice them, but in the fall they leave the trees and begin searching for a good place to spend the winter.  Unlike many other moth species whose caterpillars find such places in the fall and spin cocoons, woolly bears overwinter as the caterpillar (larva) and do not spin a cocoon and pupate until late winter or early spring.  The adult moth is not well known compared to the caterpillar, so many people don't realize that the "Isabella moth" is actually the adult woolly bear.  It is in the tiger moth family, Arctiidae, and is creamy yellow to orange, with dark orange to black speckles.  There are several species in this family that have similar-looking caterpillars to the familiar black-orange-black pattern; some have yellow instead of orange between the black bands, and some have long white hairs in the black bands, but I'll save further details for another blog!
For now, I'll leave you with some photos of what are currently overwintering in my outdoor storage closet, waiting for warmer weather to display their beautiful wings (see Rearing Lepidoptera for more information about my rearing projects).  Click on the names to see pictures of what the adults will look like.
Actias luna - luna moth
Antheraea polyphemus - polyphemus moth 
Citheronia regalis - regal moth
Hyalophora cecropia - cecropia moth (largest moth in North America, found in most states east of the Rockies)
Hyalophora euryalis - ceanothus silk moth (our northwestern version of the cecropia)
Papilio cresphontes - giant swallowtail (largest butterfly in North America) 
Papilio troilus - spicebush swallowtail


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  2. There are leaves all over the yard during the winter. Are there potential butterflies hiding among the brown dead leaves as larvae and caterpillars? Is it better not to disturb the leaves, or can I rake and move them into a pile to make the garden appear less unattractive to neighbors? Is there a particular month after which it would be safe to rake and move the leaves?

    1. Good question, there's most likely some moth pupae or cocoons, possibly woolly bear caterpillars, and other insects hiding in the leaves, less likely to have butterflies. It would be best to rake the leaves soon after they fall, but would be great if you left a pile or two, so all the creepy crawlies have time to move into the piles before winter. They may be raked up, but most would probably be sifted out during raking, so sooner the better. The leaves could be spread out as mulch in late spring, or left in a compost pile.