Vanessa Cardui - Life Cycle With Notes For Rearing in Classrooms

Life Cycle With Notes For Rearing in Classrooms

As these animals are cold blooded and their life cycle does not depend on a certain number of day/night cycles, temperature can greatly effect the times presented here.

At 90 °F (32 °C) the entire life cycles will take roughly 16 days. At 65 °F (18 °C) the life cycles will take months. At such extreme temperatures one can expect some deaths. At room temperatures the egg takes three to five days to hatch. The eggs are tiny, as tiny as a sugar crystal. They are green and ribbed and can be observed best with a magnifying glass. It is possible to view the cap at the top of the egg where the caterpillar will emerge.

The embryo can be viewed growing inside the egg using a hand lens or dissecting scope. A high powered dissecting scope allows for watching hatching quite clearly. If eggs turn deep green, or become dented and wrinkled, the eggs do not contain living embryos. Just before hatching the embryos fill the whole egg and make the eggs look black or brown. As protection against disease, newly laid eggs may be knocked off the leaf, or left attached to the leaf, and dipped in dilute household bleach solution (1 part household bleach to 200 parts water) for 1–2 minutes and swished about. Afterwards, the eggs are left on a paper towel to dry. This will kill disease on the surface of the eggs and increase caterpillar survival.

The caterpillars will emerge as small and black and will begin to eat immediately. As they grow they will shed their skins three times, called instars. At each instar the caterpillar will need much more food as it has expanded in size. It will also become more spiky. These spikes do not contain poison and are not sharp. The moulted skin appears as a black speck, what looks like dirt, near the caterpillar. Many people believe this to be the excretion of the caterpillar. Occasionally the moult will look like an entire, dead, caterpillar, as as snake's skin does. If under stress they will sometimes shed into a fifth instar, which is a very large caterpillar. A fifth instar is a sign that care is incorrect in some way, typically due to diet.

The four instars take 7–11 days to turn into a chrysalis. The caterpillar will spin a patch of silk and attach its hind end to the silk. At this point it begins changing internally, forming a "j" shape. Once the caterpillar forms a J, it should not be disturbed as it can no longer reattach itself to the silk pad. A fallen "J" caterpillar can be laid on its side on a flat piece of cotton and may shed successfully. The chrysalis is very soft at first and will dent if resting on a hard surface. After hardening, the chrysalis will crack if dropped or struck. The chrysalis can be dark or light colored depending on conditions during development of the caterpillar. It takes 7–11 days for the chrysalis to turn into a butterfly.

When emerging from the chrysalis the butterfly pumps its wings with fluid to expand them. This happens within a few minutes of emerging or cannot happen at all. Once the wings are expanded they are still soft for up to a day. Initially the butterfly prefers not to move as its wings harden, but after the wings harden for a few hours the painted lady will become incredibly sensitive to movement and will damage its still soft wings when frightened. It is best to wait a full day after emergence from the chrysalis to handle a painted lady. Its wing span is 2 inches (50 mm).