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Migration

Unlike most other insects in temperate climates, monarch butterflies cannot survive a long cold winter. Every fall, North American monarchs fly south to spend the winter at roosting sites. Monarchs are the only butterflies to make such a long, two-way migration, flying up to 3000 miles in the fall to reach their winter destination. Amazingly, they fly in masses to the same winter roosts, often to the exact same trees. Their migration is more the type we expect from birds or whales than insects. However, unlike birds and whales, individuals only make the trip once. It is their children’s grandchildren that return south the following fall.

Some other species of Lepidoptera (butterflies and moths) travel long distances, but they generally go in one direction only, often following food. This one-way movement is properly called emigration. In tropical lands, butterflies do migrate back and forth as the seasons change. At the beginning of the dry season, the food plants shrivel and the butterflies leave to find a moister climate. When the rains arrive, the food plants grow back and the butterflies return.

Monarch butterflies have a complicated life cycle , in that monarchs emerging at different times of the year do different things. Monarchs that emerge in the spring and summer months become reproductive within a few days. Monarchs emerging in the fall are in reproductive diapause, which is a state of suspended development of the reproductive organs. Even though these butterflies look like summer adults, they won’t mate or lay eggs until the following spring. Monarchs have to know when to fly south, and also when to begin the journey back north.

When the late summer and early fall monarchs emerge from their pupae, they are physically and behaviorally different from those emerging in the summer. The shorter days, cooler air, and milkweed senescence (aging) of late summer trigger changes. In the northern part of their range, this occurs around the end of August, when monarchs begin to emerge in reproductive diapause. Diapause is controlled by the nervous system and by hormones. Environmental factors signaling the onset of unfavorable conditions are involved in triggering this physiological response. These factors include day length, temperature, and host plant quality.

Day Length: Decreasing daylength is one of the most important factors that cause monarchs to emerge in reproductive diapause. In a series of experiments, Liz Goehring (U of MN graduate student scientist) found that monarchs reared under constant short and long daylengths were mostly reproductive, while those reared under decreasing daylength were more likely to be in diapause. Therefore, she concluded that it is the change in daylength that is an important cue, rather than absolute day length.

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By Katrin Bennhold and Frye Phillip Harness Tall Wide Calf F3Xg0

BERLIN — Chancellor Angela Merkel, who staked her legacy on welcoming hundreds of thousands of migrants into Germany, agreed on Monday to build border camps for asylum seekers and to tighten the border with Austria in a political deal to save her government.

It was a spectacular turnabout for a leader who has been seen as the standard-bearer of the liberal European order but who has come under intense pressure at home from the far right and from conservatives in her governing coalition over her migration policy.

Although the move to appease the conservatives exposed her growing political weakness, Ms. Merkel will limp on as chancellor. For how long is unclear. The nationalism and anti-migrant sentiment that has challenged multilateralism elsewhere in Europe is taking root — fast — in mainstream German politics.

Ms. Merkel agreed to the latest policy after an insurrection over migration policy led by her interior minister, Horst Seehofer , threatened to bring down her coalition.

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