Whether driving rural backroads or relaxing on a porch in town, it’s not uncommon to see a flurry of black and orange fill the air.

Monarch butterflies have been making their way through northeastern South Dakota for more than a week now as they migrate to Mexico.

Sometimes they can be seen clustered in trees, almost like grapes. Last week, there were large numbers of them at the Granary Rural Cultural Center near Groton.

Jodie Ramsay and Eric Pullis, biologists from Northern State University, answered some questions about the migration.

Q: Why have we been seeing them in clusters in trees?

A: This time of year monarchs are migrating south. After spending the day traveling they pick out areas to roost. Roosting spots appear to have a favorable micro-climate out of wind and are reasonably close to a food source, which is flowers, where they can feed before continuing along their way.

Q: Why do some appear sluggish when it’s cooler?

A: Monarchs, like all insects, are cold-blooded. When the temperature is too low they are unable to fly until it warms up or the sun shines on them, so they will be lethargic and sluggish. Once the temperature warms up and the conditions are favorable they can begin flying around.

Q: What makes for a good hatch of caterpillars?

A: Good weather conditions, but we still don’t know a lot of the factors that contribute to good and bad years. The monarch caterpillars feed exclusively on milkweeds, so milkweed numbers will influence the number of monarchs that can be around. Milkweeds are very susceptible to herbicides, so as their habitat has declined, so have the monarchs. The yearly count of monarchs overwintering in Mexico was down last year due to late spring freezes and an unseasonably warm fall that kept some monarchs from migrating.

Q: How long will they stick around?

A: Maybe a couple weeks, but it is likely that most individuals are not staying in the area that long. Individual monarchs won’t make it the whole way (to Mexico), but their offspring can.

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