As the lilacs bloom in late May and early June, the first monarch butterflies flutter into Northern Minnesota. Most years, they are joined by tiger swallowtails, which are non-migratory but emerge from chrysalises within days of the monarchs showing up. The reason for this apparent synchrony is unknown, but staff phenologist John Latimer has watched it with interest for many years.
The monarchs flying north are not the same ones that we saw depart last fall; they are the fall migrator’s children. The fall migrators overwinter in Mexico, fly to the southern US in spring, and lay eggs; those eggs hatch into very hungry caterpillars, which metamorphose into adults, which eventually flutter into our neck of the woods in late May and early June.
Meanwhile, the tiger swallowtails are chilling out (quite literally) in their chrysalises as pupae. The pupae produce a natural antifreeze that protects its cells from damage by freezing.
This biologically produced antifreeze has two functions: It reduces the size of any ice crystals that form in the body, so that they don’t puncture cells or displace organs. Secondly, it changes the makeup of the fluid inside the cells to lower its freezing point, ensuring that ice crystals do not form within the delicate cell walls.
In spring, the swallowtail pupae thaw out, restart metamorphosis, and at last emerge as vibrant yellow-and-black butterflies—just as the monarchs flap into view.
Why do monarchs and swallowtails sync up in this way? There are a variety of potential testable answers—availability of food resources, response to day length, predator avoidance, and so on—but I like to think that they just enjoy each other's company.
Topics
- Introduction (0:00-0:22)
- Monarchs and tiger swallowtails (0:22-4:07)
- Insects (4:07-6:28)
- Molt-migrating Canada Geese (6:28-7:43)
- Frogs calling (7:43-8:45)
- Shrubs (8:45-11:26)
- Herbaceous plants (11:26-17:25)
- Trees (17:25-19:22)
- Driftless region phenology (19:22-21:10)
- Conclusion (21:10-22:24)
What have you seen out there? Let us know: email us at comments@kaxe.org or text us at 218-326-1234.
That does it for this week! For more phenology, <b>subscribe</b> to our Season Watch Newsletter or visit the Season Watch Facebook page.
Funding for this project was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR).
