Regal Fritillary: A Rare Butterfly That Is Thriving in Three Rivers

By: John Moriarty

November 30, 2020

Category: Resource Management

Sometimes confused with monarchs, regal fritillaries are large orange, black and silver butterflies that are found in prairies and other native grasslands. They used to be found from the Great Plains all the way to the Atlantic Ocean, but they are now gone from most of their original range.  

This decline is mainly caused by the loss of grasslands to agriculture. In Minnesota, regal fritillaries are considered rare. They are listed as a Species of Greatest Conservation Need (SGCN) and a Species of Special Concern (SSC). These designations from the Minnesota Department of Natural Resources are what encouraged us to reintroduce these butterflies into Three Rivers and help in their conservation.

The Life of a Regal Fritillary

Regal fritillaries emerge from their chrysalises as adults in early July. They only have one generation per year. Other butterflies, like monarchs, may have four or five generations per year. 

Males come out first followed by females one to two weeks later. The males are easier to see as they fly across the prairies searching for females to breed with. The females come out to nectar on the flowers and then stay down in the vegetation. 

Adult regal fritillaries feed on a variety of flower nectars.  They are commonly seen on butterfly weed, wild bergamot and blazing stars.  

A great spangled fritillary and a regal fritillary nectar on butterfly weed.
A great-spangled fritillary (left) and a regal fritillary (right) nectar on butterfly weed. "Regal Fritillary on right, Great Spangled Fritillary on left" by ShenandoahNPS is marked with CC PDM 1.0.

By mid-August the males have died out, but the females are still around laying their eggs. A single female can lay up to 2,000 eggs.

The caterpillars hatch in September, three to four weeks after the eggs are laid. These tiny (less than ¼ inch) caterpillars crawl to the base of a prairie plant and go into a diapause (period of inactivity, kind of like a very long nap) for the winter.

Regal fritillary caterpillars are very particular about what they eat. They only eat prairie violet leaves, so they are normally only found on remnant prairies that still have a good population of violets. Most restored prairies do not have violets because the seeds are difficult to collect and the plants are expensive to buy and plant.  

The caterpillars will grow to about 1 ½ inches before they form a chrysalis. During that time they will have gone through six instars, or stages where they shed their skin and grow bigger. They will emerge from the chrysalis in two to three weeks as an adult.

Reintroducing Regal Fritillaries at Crow-Hassan

At Crow-Hassan Park Reserve, we planted approximately 1,000 prairie violets in the 1990s through a grant. We occasionally saw violets in the spring but were not sure how many there were across the prairie. When we started thinking about reintroducing regal fritillaries, we knew we would have to increase the density of violets so there would be enough food for potentially thousands of hungry caterpillars. 

From 2014 to 2018 we purchased and planted 10,000 large prairie violets (2,500 per year). This was paid for through grants and donations.    
In August 2016, our wildlife staff traveled to prairies in the southwest and southeast Minnesota to collect adult regal fritillaries, especially females. We caught 25 butterflies and released them into the prairie at Crow-Hassan.

The following July, we started two different surveys to monitor regal fritillary populations at Crow-Hassan. One was a series of seven transects across the prairie that we walked three times a year and recorded how many butterflies we saw. The second was an area search where wildlife staff and volunteers tried to catch all the regal fritillaries found in three 5-acre blocks. The transect survey gave us the relative abundance of regal fritillaries compared to other butterfly species, and the block searches gave us the density of regal fritillaries per acre.

Three Rivers employees walk through the prairie with nets, looking for regal fritillary butterflies.
Three Rivers Wildlife staff walk the prairie looking for regal fritillaries.
A park district employee holds a regal fritillary she caught.
Staff catch regal fritillaries as part of a survey to understand how the population at Crow-Hassan is doing. 
A hand holds a stack of butterflies in small envelopes.
The butterflies are placed in small envelopes to ensure none are double-counted. They are released after counting.
Park district employees stand around a table to record butterfly survey information.
Wildlife staff record regal fritillary data before releasing the butterflies back onto the prairie.

In 2017, we saw an average of two regal fritillaries per transect and 3.2 butterflies per acre in the block search. In 2018 and 2019, we averaged 15 butterflies per transect and 8.5 per acre.  

While this may not sound like a lot, when you expand the number over 850 acres of prairie, you end up with over 7,000 butterflies. Even if we are conservative in the amount of land occupied by regal fritillaries – a third of the prairie, or approximately 280 acres – we still have over 2,000 butterflies.  Considering we started with 25 butterflies only two years earlier, that is a great success.  

We did not do any official surveys in 2020, but we regularly saw regal fritillaries across the prairie in July, and we continued to see females in early September.

After the success of the regal fritillary, we are investigating several other species of prairie butterflies to reintroduce into Crow-Hassan. 

To learn more about at-risk and vulnerable wildlife in Minnesota, check out new episodes of The Wandering Naturalist podcast this Wednesday. 

 

Archive image: "Regal fritillary butterfly" by U.S. Army Environmental Command is licensed under CC BY 2.0.

About the Author

 a man in a hat and tan collared shirt holding a turtle upside down and pointing to it's underbelly.

John Moriarty is the Senior Manager of Wildlife at Three Rivers Park District and has been with the Park District for 15 years. He has been involved in many of the wildlife restoration efforts and initiated the snake and butterfly efforts. John has led several projects to increase prairie habitat in the Park District. John likes exploring natural areas and looking for all types of plants and animals, but especially turtles.

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