Butterfly zoos are open to the public. A double-entry door is usually used to ensure that no butterflies escape. Exploration of such zoos may be with a guide or on one's own, at leisure. Guided tours may last about fifteen minutes, as the guide points out all the species of butterflies that are in the greenhouse that day (new shipments usually arrive weekly, and stocks vary). Guides may also show butterfly eggs, caterpillars, and chrysalids and identify specific plants that are favored by each species. Between 10 a.m. and 1 p.m. is usually the best time to see butterflies emerging from their pupae. Butterflies are most active on warm and sunny days with little wind, because they require the heat of the sun to aid in their digestion. On rainy days, they usually hide in the flowers and leaves. There are often many different species in such zoos, with stock including butterflies from Africa, Malaysia, South America, Thailand, New Guinea, Costa Rica, the Philippines, and other places. The vibrant colors and patterns on the wings of the insects have earned them the fanciful nickname "flying flowers". One should wear a light floral perfume and wear bright-colored or bright-white clothing to encourage the butterflies to land upon oneself, but one should never touch a butterfly. Butterflies are attracted to a bright Hawaiian print shirt for the same reason they are attracted to flowers, but a person's touch will cause damage to their sensitive wings because of the oils in people's skin and their easily damaged scales. Many species of adult butterfly live only one to two weeks, during which time they must produce a new generation. Some species, such as the familiar Monarch butterfly, however, can live as long as six months or even longer in the wild. A chrysalis (Latin chrysallis, from Greek ? = chrysallis, pl: chrysalides, also known as an aurelia) or nympha is the pupal stage of butterflies. The term is derived from the metallic gold-coloration found in the pupae of many butterflies, referred to by the G eek term (chrysos) for gold. When the caterpillar is fully grown, it makes a button of silk which it uses to fasten its body to a leaf or a twig. Then the caterpillar's skin comes off for the final time. Under this old skin is a hard skin called a chrysalis.[4] Because chrysalides are often showy and are formed in the open, they are the most familiar examples of pupae. Most chrysalides are attached to a surface by a Velcro-like arrangement of a silken pad spun by the caterpillar, usually cemented to the underside of a perch, and the cremastral hook or hooks protruding from the rear of the chrysalis or cremaster at the tip of the pupal abdomen by which the caterpillar fixes itself to the pad of silk. (Gr. 'kremastos'=suspend) [5] Like other types of pupae, the chrysalis stage in most butterflies is one in which there is little movement. However, some butterfly pupae are capable of moving the abdominal segments to produce sounds or to scare away potential predators. Within the chrysalis, growth and differentiation occur. The adult butterfly emerges (ecloses) from this and expands its wings by pumping haemolymph into the wing veins.[6] Although this sudden and rapid change from pupa to imago is often called metamorphosis, metamorphosis is really the whole series of changes that an insect undergoes from egg to adult. On emerging the butterfly uses a liquid which softens the shell of the chrysalis. Additionally, it uses two sharp claws located on the thick joints at the base of the forewings to help make its way out.[7] Having emerged from the chrysalis, the butterfly will usually sit on the empty shell in order to expand and harden its wings. However, if the chrysalis was near the ground (such as if it fell off from its silk pad), the butterfly would find another vertical surface to rest upon and harden its wings (such as a wall or fence). Moth pupae are usually dark in color and either formed in underground cells, loose in the soil, or their pupa is contained in a protective silk case called a cocoon.