The monarch butterfly is one of the most recognised insects in North America - and it's on the verge of federal protection. USFWS found that ESA listing is warranted but precluded by higher-priority actions, making the monarch a candidate species under the ESA. A final listing decision could come at any time.
For environmental consultants and developers, the question is practical: what does this mean for projects right now, and what changes when the listing becomes final?
Current Status
The monarch butterfly (Danaus plexippus) is currently an ESA Candidate Species. This means USFWS has determined that listing as Threatened or Endangered is warranted based on population declines, but the agency hasn't yet issued a final listing rule because other species have higher priority.
Candidate status does not carry the legal protections of a listed species. There are no Section 7 consultation requirements, no Critical Habitat designation, and no prohibition on take. However, USFWS strongly encourages voluntary conservation measures for candidate species, and many federal agencies already consider monarchs in their environmental reviews as a matter of policy.
The key point for project planning: if you're working on a project with a 2-3 year timeline, the monarch may well be listed before your project reaches construction. Planning for it now avoids costly redesigns later.
Why Monarchs Are Declining
The eastern migratory population of monarch butterflies has declined by approximately 80% since the mid-1990s. The western population has experienced even steeper declines. The primary drivers are:
Habitat loss. Conversion of grasslands, prairies, and agricultural margins to cropland and development has eliminated vast areas of milkweed - the only plant genus that monarch caterpillars can eat. An estimated 1.3 billion milkweed stems have been lost from the agricultural landscape since the late 1990s.
Herbicide use. The adoption of herbicide-tolerant crops has led to widespread elimination of milkweed from agricultural fields where it previously coexisted with crops.
Climate change. Altered precipitation patterns, extreme heat events, and shifting seasons affect monarch breeding, migration timing, and overwintering habitat quality.
Overwintering habitat degradation. The oyamel fir forests in central Mexico where eastern monarchs overwinter have been affected by illegal logging, storms, and climate change. Western monarchs overwinter in coastal California groves that face development pressure.
What Happens When Monarchs Are Listed
When the listing rule is finalised, the following changes take effect:
Section 7 consultation. Any project with a federal nexus (federal funding, federal permit, federal land) that may affect monarchs will require Section 7 consultation with USFWS. This applies to projects in monarch habitat - anywhere milkweed or nectar resources are present during the breeding season (roughly April - September across most of the US).
Prohibition on take. It becomes illegal to kill, harm, harass, or pursue monarchs without authorisation. "Harm" under the ESA includes significant habitat modification that actually kills or injures wildlife. Large-scale removal of milkweed or nectar plants during the breeding season could constitute take.
Critical Habitat designation. USFWS may designate Critical Habitat for monarchs, though the geographic scope would be enormous given the species' continental range. Critical Habitat designation triggers additional consultation requirements for federal nexus projects.
Section 10 permits. Non-federal entities that anticipate incidental take of monarchs (e.g., agricultural operations, development projects, roadside mowing) may need Habitat Conservation Plans and Incidental Take Permits under Section 10.
What It Means for Development Projects
Projects in Monarch Habitat
Monarch habitat is broadly defined. Any site with milkweed (Asclepias species), wildflower meadows, prairie remnants, old fields, or agricultural margins may support breeding monarchs from April through September. Monarchs also use a wide range of nectar-producing plants during migration.
If your project involves:
- Clearing grassland, prairie, or old field habitat
- Removing vegetation along roadsides, utility corridors, or fence lines
- Converting agricultural land with milkweed to development
- Any land disturbance during the breeding season (April - September)
You should assess whether monarch habitat is present and factor potential listing into your project timeline.
Current Best Practice (Pre-Listing)
Even though monarchs aren't yet listed, many federal agencies and state DOTs already include monarchs in their environmental reviews. Current best practices include:
Habitat assessment. Survey the project area for milkweed species and nectar resources during the growing season. Document the species, density, and extent of milkweed patches.
Seasonal avoidance. Where possible, schedule vegetation clearing and ground disturbance outside the monarch breeding season (avoid May - September when caterpillars and eggs are present on milkweed).
Habitat creation. Incorporate pollinator-friendly plantings into project landscaping plans. Seed disturbed areas with native milkweed and wildflower mixes appropriate for your region.
Voluntary conservation agreements. USFWS offers Candidate Conservation Agreements (CCAs) and Candidate Conservation Agreements with Assurances (CCAAs) for candidate species. These agreements provide regulatory predictability - if you implement agreed conservation measures now, you receive assurances that no additional measures will be required if the species is listed.
Post-Listing Requirements
Once listed, projects with a federal nexus will need to:
Screen for monarch habitat during desktop assessment. Check for milkweed occurrence records, prairie/grassland habitats, and proximity to known migratory corridors.
Conduct habitat assessments during the growing season to document milkweed and nectar resources.
Avoid or minimise impacts to milkweed patches and nectar resources during the breeding season.
Consult with USFWS under Section 7 if the project may affect monarchs or their habitat.
Mitigate unavoidable impacts through habitat creation, milkweed planting, or conservation contributions.
Survey Protocol
There is no standardised USFWS survey protocol for monarchs yet (unlike bats or birds). Current best practice for assessing monarch habitat includes:
Desktop screening. Check for known monarch occurrence records using EcoCheck or GBIF. Review aerial imagery for potential habitat (grasslands, prairies, old fields, roadsides). Check the Monarch Conservation Science Partnership database for migration and breeding data.
Field habitat assessment. Walk the project area during the growing season (June - August is optimal). Record:
- Milkweed species present and stem density
- Nectar plant species and abundance
- Habitat type (grassland, prairie, old field, roadside, agricultural margin)
- Evidence of monarch use (adults, eggs on milkweed, caterpillars, chrysalides)
Survey timing. June - August for breeding habitat assessment. September - October for fall migration corridor assessment. Milkweed identification is most reliable when plants are flowering (June - August).
Survey effort. 1-2 site visits during the breeding season for a standard habitat assessment. Larger sites or corridor projects may need multiple visits.
Milkweed Identification
Knowing your milkweed species is essential. Common milkweed species used by monarchs include:
Common milkweed (Asclepias syriaca) - the most widespread species. Found throughout the eastern US in fields, roadsides, and disturbed areas. Pink-purple flower clusters, broad opposite leaves, milky sap.
Swamp milkweed (Asclepias incarnata) - found in wet meadows, stream banks, and wetland edges. Pink flowers, narrower leaves than common milkweed.
Butterfly weed (Asclepias tuberosa) - found in dry prairies, meadows, and roadsides. Distinctive orange flowers. Does not have milky sap (unusual for milkweeds).
Tropical milkweed (Asclepias curassavica) - found in the southern US. Red and yellow flowers. Non-native but widely planted in gardens. Controversial because it may disrupt migration patterns if it doesn't die back in winter.
Whorled milkweed (Asclepias verticillata) - found in dry prairies and pastures. Small white flowers, narrow whorled leaves.
There are over 70 native milkweed species in North America. Regional field guides and your state's natural heritage program can help with identification.
What EcoCheck Shows You
EcoCheck US searches GBIF for monarch butterfly occurrence records near your project location. The results show:
- Number of monarch records within your search buffer
- Year range of observations
- Data sources (iNaturalist, eButterfly, research collections)
- Individual record locations on the map
Monarch records in your search area indicate the species uses the area during breeding or migration. Combined with a habitat assessment for milkweed, this informs whether your project needs to address monarchs in its environmental review.
For corridor projects (pipelines, transmission lines, road widening), the Corridor Search feature identifies which sections of your route have the highest concentration of monarch records and where habitat assessment should focus.
Plan Ahead
The monarch listing is not a matter of if, but when. Projects with multi-year timelines should factor monarch conservation into their planning now. The cost of a habitat assessment and seasonal avoidance measures is minimal compared to the cost of a project delay when the listing becomes final mid-construction.
Voluntary conservation measures implemented before listing can also provide regulatory benefits through Candidate Conservation Agreements, giving you predictability and potentially avoiding additional requirements post-listing.
Patrick O'Connor is a Freelance Ecologist at Kinterra Consulting and the developer of EcoCheck US - an instant ecological desktop assessment tool for any US location. Try it free at ecocheckus.com.