Wing span: 9.0-10 cm.

Flight time: While some migrants will return as soon as early-April, the bulk arrive from mid-May to mid-June. These found a series of overlapping generations, with emergences from late-July through August. In September, adults congregate and begin the southern migration to their wintering grounds in the mountains of central Mexico.

**The monarch is a spring and early-summer southern migrant; mid and late-summer resident.

Distinguishing features: This is one of our most conspicuous butterflies; a description is hardly necessary. Wings are large, bright orange, with black line and a black margin with white spots. Unlike the viceroy, they lack black line crossing the hindwing.

Distribution and habitat: Map 573. Abundant throughout the state in a wide variety of open habitats, wherever its host plant grows in abundance. As such, it is frequent in disturbed sites.

Natural History: Larvae consume various species of milkweed, especially the common milkweed (Asclepias syriaca). Adult population sizes slowly climb until mid-September when the bulk of the migration passes through Iowa. Their annual routes have been studied for many years by Urquhart (1960) and others who are assisted each year by hundreds of co-workers, including Iowans, in applying wing-tags to help trace distances and directions traveled. Eventually the wintering site was located in the Sierra Madre Mountains of central Mexico. During migration they may gather in great numbers on trees, often on high points, or in wind-protected areas for a day or two before continuing their southward journey. The same roosting points may be used year after year. The continued existence of this species may be in more jeopardy than its current distribution suggests. Deforestation in the Mexican highlands has increased the frequency of killings frosts. Millions perished in a single night in late December 1995. Given that much of our common milkweed plants live in ditches and fence rows immediately adjacent to croplands, methods of controlling crop pests may well have serious negative impacts.