Wow! What a wonderful question. The answer can take days to write so we'll take them one or two species at a time.
Viceroy and Red-Spotted Purple butterflies can be attracted to your yard with fruit. They will feed on flower nectar and decaying fruit. A bird suet feeder, an apple, a fruit tree; nearly any type of fruit is acceptable to these beautiful winged creatures.
Viceroy butterflies lay eggs on willow leaves. Red-Spotted Purple butterflies lay eggs on willow or black cherry leaves.
The female butterfly of these two species lands on a leaf, turns around, and backs down until her abdomen touches a point of the leaf. The point is normally the tip of the leaf. If a leaf has been torn, the point could be another tip of the leaf, on the side of the leaf. When searching for eggs, look on the tips of the leaves as well as jagged edges. Almost all eggs will be found on the tip of the leaf.
The egg is green. Through a microscope, the egg resembles a sand spur. It has points all over the outside of the egg.
A young caterpillar will start eating the tip of the leaf. It will take its frass (excrement) and add a small bit to the tip of the leaf vein. When not eating, the caterpillar will rest on the extended leaf vein (excrement) and as it grows, it rests on the leaf vein.
As the caterpillar continues to grow (multiplying its hatchling weight by 2,500) it grows too large to rest upon a leaf vein. It begins to eat so much, it will eat several leaves per day. At this point it will rest on the twig of the tree. A larger caterpillar may be brown or green. It blends in well with the tree itself and is difficult to spot until one develops an 'eye' for caterpillars.
In the fall, before the leaves drop, a Viceroy or Red-Spotted Purple caterpillar that is approximately 3/4" long will eat a little over half a leaf. It will then sew the leaf to the twig with silk from its spinnerets (located under its mouth). It will next lay a thick layer of silk from side to side of the leaf, starting with the petiole, where the leaf 'stem' joins the leaf itself. As the silk dries, it contracts and draws the edges of the leaf together to form a tube that is open at one end. The caterpillar will crawl into this tube when days become very short (and nights become long). By this time, fall has arrived and leaves have started falling off the trees. The tube, called a hibernaculum, will not fall from the twig simply because the caterpillar literally sewed it to the twig.
It survives freezing temperatures for days at this point because it has gone into diapause. Sorbitol and glycerol are in the caterpillars blood, preventing it from freezing, like anti-freeze. When the days become longer (and nights shorter) fresh leaves will grow on the tree. The caterpillar will crawl backward out of the hibernaculum to eat these fresh leaves. It will return to the hibernaculum when resting until it grows too large for the tiny leaf tube.So ....
~ Eggs; look on the tips of leaves, first checking younger leaves before looking at older leaves.
~ Caterpillars spring and summer and early fall; look on the tips of leaves for a young hatchling caterpillar and on the leaf vein for caterpillars a little older. Look on twigs for larger caterpillars.
~ Caterpillars in late fall and winter; look for hibernaculums on bare twigs. If a hibernaculum is found, a small ribbon can be tied 12 - 24 inches from the hibernaculum. In the spring, when fresh leaves are growing, the area around the hibernaculum should be checked almost daily for a young caterpillar. If a hibernaculum with a caterpillar is taken indoors in the winter, the caterpillar can become dehydrated from the dry indoor air and/or the longer periods of light indoors may cause it to come out of diapause. Without fresh leaves to eat, it will starve.
Happy hunting for Viceroy and Red-spotted Purple butterfly eggs and caterpillars!
(Watch for a post soon detailing how to tell the difference between Viceroy and Red-Spotted Purple caterpillars. Hint; it's the spikes on the humps!)
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