Coloured scanning electron micrograph (SEM) of Monarch butterfly wing scales (Danaus plexippus). Monarch butterfly wings have a dense concentration of scales to Monarch butterfly wings have narrower wing veins plus a spot of dense scales on each hind wing. The spot is a scent gland. Males use the pheromones produced by this gland to make themselves attractive to females. In two to five weeks of egg-laying a female will lay about 700 eggs. Generally, eggs hatch in 4 days, but cool temperatures delay hatching up to 12 days. Newly hatched caterpillars feed on milkweed, their sole source of food. Milkweed contains a poison that is harmless to monarchs, but which sickens predators. A caterpillar eventually attaches itself to a twig, sheds and forms a chrysalis from which an adult monarch butterfly emerges. An adult lives six weeks in summer but those that migrate can live six to nine months over winter. Magnification: x50 when shortest axis printed at 25.
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