GAINESVILLE, Fla. (WCJB)- Hannah Vander Zanden is an Assistant Professor at the University of Florida's Department of Biology. She explains, "There's been a lot of interest in what's happening between Monarchs because their numbers in their overwintering grounds have been declining in the last several decades."
Eastern Monarch Butterflies are known for their incredible fall migrations to Mexico, but there are some Monarchs that don't migrate. Despite being the same species, migratory Monarchs and residential Monarchs weren't thought to interact or change behaviors. Research from the University of Florida theorizes that the resident Monarchs in Florida were once migratory Monarchs.
"About half of the individuals sampled in South Florida came from outside of the state"
Hannah Vander Zanden explains her team took samples of the wings of monarch butterflies and were able to track where they were as a caterpillar based on the hydrogen and carbon present. More than half of their samples from South Florida were butterflies that were from the midwest, and were even as far north as Canada. "What we don't know is if they go back north in the spring".
Vander Zanden says she doesn't know why Monarchs decided to go to Florida instead of Mexico. She says it might be because they weren't healthy enough to make the trip to Mexico, or there may be more food available than before because more people are planting milkweed. She says it's possible Florida's residential monarchs wouldn't be sustainable unless new monarchs were coming in from other places because of a parasite that is killing off many of South Florida's Monarch Butterflies.