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V. cardui is one of the most widespread of all butterflies, found on every continent except Antarctica and South America. In Australia, V. cardui has a limited range around Bunbury, Fremantle, and Rottnest Island. However, its close relative, the Australian Painted Lady (Vanessa kershawi, sometimes considered a subspecies) ranges over half the continent. Other closely related species are the American Painted Lady (Vanessa virginiensis) and the West Coast Lady (Vanessa annabella).
Vanessa cardui occurs in any temperate zone, including mountains in the tropics. The species is resident only in warmer areas, but migrates in spring, and sometimes again in autumn. It migrates from North Africa and the Mediterranean to Britain in May and June, but for decades natualists have debated whether the offspring of these immigrants ever make a southwards return migration. Recent research suggests that British painted ladies do undertake an autumn migration. Using an entomological radar, scientists at Rothamsted Research provided evidence that autumn migrations take place at high altitude, which could be why these migrations are seldom witnessed.
Relationship with humans
Vanessa cardui butterflies are raised in many preschool and elementary classrooms to demonstrate the life cycle of a butterfly. Naturally, this is one reason they are so popular amongst children. They are also often found in science fair projects.
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).
The painted lady uses over 300 recorded host plants according to the HOSTS database. For raising in the classroom one need only sprout a bed of black oil sunflower seeds, as are used for bird seed. The caterpillars will eat the true adult leave (not the sprouts) and in this way one may inexpensively produce many host plants. Soak the seeds for eight hours in 10% diluted household bleach (1 pt bleach, 9 pts water) to ensure a disease free, even sprouting. Place the seeds upon the surface of the soil and keep moist until they grow roots and can be watered normally.
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- "Painted Lady". A-Z of Butterflies. Butterfly Conservation. http://www.butterfly-conservation.org/butterfly/32/butterfly.html?butterflyid=38. Retrieved 22 October 2012.
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- Vanessa cardui, Butterflies of Canada
- "Vanessa cardui". HOSTS - a Database of the World's Lepidopteran Hostplants. The Natural History Museum. http://www.nhm.ac.uk/research-curation/research/projects/hostplants/search/list.dsml?searchPageURL=browse.dsml&Family=Nymphalidae&Genus=Vanessa&Species=cardui&Country=&sort=Family. Retrieved 22 October 2012.
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- Chapman, Jason W.; Nesbit, Rebecca L.; Burgin, Laura E.; Reynolds, Don R.; Smith, Alan D.; Middleton, Douglas R.; Hill, Jane K. (2010). "Flight Orientation Behaviors Promote Optimal Migration Trajectories in High-Flying Insects". Science 327 (5966): 682–5. doi:10.1126/science.1182990. PMID 20133570.
- Nesbit, R.L.; Hill, J.K.; Woiwod, I.P.; Sivell, D.; Bensusan, K.J.; Chapman, J.W. (2009). "Seasonally adaptive migratory headings mediated by a sun compass in the painted lady butterfly, Vanessa cardui". Animal Behaviour 78 (5): 1119–25. doi:10.1016/j.anbehav.2009.07.039.