Tuesday, August 19, 2008

Where have all the monarchs gone?

Monarch Butterfly Feeding on Milkweed
When we walked the dunes of Kohler-Andrae State Park, it was fun to watch the monarch butterflies, glowing bright orange in the sun, flitting lazily among the milkweeds (they seem to be fussy eaters, doing a lot of research to scout out just the right meal.) The the symbiotic relationship between milkweeds and monarchs is so tight that they're sometimes referred to as milkweed butterflies. The adults can and do get their nectar in many places, but they like milkweed flowers and also lay their eggs on the plant. The larvae eat only milkweed leaves, absorbing chemicals from the milkweed that are toxic or unpleasant to many animals. Traces remain in the adult butterfly, whose distinctive color and markings serve to remind predators who have tried to eat one not to repeat the mistake. Simple aversion therapy.

Although we saw many monarchs at Kohler-Andrae, there were not as many as other years. Where have all the monarchs gone? Weather plays a huge role in their lives and their remarkable trans-generational migratory journey to Mexico and back. In recent years cold weather in Mexico decimated their numbers, but Monarchs are remarkable in their ability to bounce back from unusual weather stress. This year, the villain seems to have been the awful rains earlier this year along their migratory route back up north. They can't fly in the rain, and the rain also disrupted the growing season of many of the plants they feed on enroute.

They'll recover from this year's rains, as well -- but declining milkweed habitat is a continuing long-term threat. Milkweed makes cows sick, so farmers get rid of it in pasture land. But a bigger threat to monarch ecology is urban development. There's not a lot of milkweed growing in parking lots, and very little in the lawns and gardens of suburbia. If you get a chance, plant some milkweed in your garden. The monarchs will thank you.

1 comment:

Nataraj Hauser said...

You'll be happy to know that I let my milkweed volunteers run rampant around the house this year. Doin' my part...