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Case Studies: Three Examples of Insects & the ESA

Nov 24, 2020

Cover photo of a rusty patched bumble bee by Xerces Society / Rich Hatfield. 

While we do not know what will happen in the upcoming ESA listing decision for monarch butterflies, we can explore how the listing process has looked for three other insects. These include examples of species where the USFWS found that listing was (1) warranted; (2) not warranted; and (3) warranted but precluded. Click on the links to see how each decision is announced on the Federal Register. 

To read more about the listing decision process and what we know so far about the upcoming decision for monarch butterflies, please check out our blog post: 

Coming Soon: Proposed ESA Listing Decision for Monarch Butterflies


San Joaquin Valley giant flower-loving fly

A petition to list the San Joaquin Valley giant flower-loving fly was submitted in June of 2014. In April of 2015, the service determined that the petition presented enough information that a larger species status assessment was needed. In December 2018, the results of the species status assessment led the USFWS to conclude that listing was not warranted. When listing is not warranted, a number of species are often included in the same announcement.


Puerto Rican harlequin butterfly

Listing of the Puerto Rican harlequin butterfly was initially determined in 2011 to be “warranted but precluded”. This meant that the harlequin butterfly became a candidate species, to be re-evaluated for listing in the future. With new data in October of 2020, the USFWS has announced that listing the harlequin butterfly as a threatened species is warranted. Their proposed ruling includes a special 4(d) rule. As of November 2020, the comment period is open for this proposed ruling. 


Rusty patched bumble bee

A petition to list the rusty patched bumble bee was originally filed by the Xerces Society in 2013. In September 2016, the USFWS announced that it found that listing the rusty patched bumble bee as an endangered species was warranted. This was the proposed rule. Following a 60-day comment period and additional assessment by the USFWS, the finaling ruling of endangered species status was announced in January 2017.


The Monarch Joint Venture is a national partnership of federal and state agencies, non-governmental organizations, businesses and academic programs working together to conserve the monarch butterfly migration. The content in this article does not necessarily reflect the positions of all Monarch Joint Venture partners. Cover photo by Xerces Society / Rich Hatfield​​​​​​​.