Andrena grindeliae

Justification:
Andrena grindeliae is a solitary bee species known from just eight observations. It occurs in central California, from the San Francisco Bay area east to the Sierra Nevada range. Using all observations of the species the extent of occurrence (EOO) is 8,398 km2. This species is only known from four localities, so there is a low degree of confidence in the accuracy of the EOO. Additionally, the species has not been observed since 1973, so it is unclear if it is still extant throughout its known range. This species likely occurs in just four locations if each locality is impacted by threats independently. All four documented localities of this species are now medium intensity urban development or developed open space. The habitat conditions at the time of collections are not well understood. It is possible localities of this species are no longer habitat supportive to the species. This species may also be threatened by climate change and exposure to pesticides, which have been observed across its range. More information is needed to determine if this species is still extant, and to better understand its life history and the degree to which it is impacted by threats. Because this species is known from an extent of occurrence that is less than 20,000 km2, is known from just four locations, and has seen habitat loss due to urban development in its range, it is assessed as Vulnerable B1abiii.

Food habits comment: Few records of this species overall contribute to uncertainty about the dietary breadth of Andrena grindeliae. It has been recorded foraging from Baccharsi pilularis, Hezimonia congesta, and Grindelia spp. (Asher and Pickering 2025). Habitat comment: All localities of this species come from what is now medium intensity development, or developed open space. It is not clear what the condition of the localities was at the time of collection. Records come from the Central California foothills and coastal mountains and Sierra Nevada range, between 30 and 2,481 m. Reproduction comment: This species likely nests underground like all other Andrena (Danforth et al. 2019), but nests from this species have not been described. Nest cells from other members of this genus are located at the ends of the lateral burrows, which are typically lined with a waxy Dufour’s gland secretion (Cane 1981) that serves to both isolate the provision from pathogens in the surrounding soil and to regulate water uptake from the soil atmosphere (Cane and Love 2021). Females provision each cell with a ball of pollen moistened with nectar on which they lay a single egg (Michener 2007). Phenology comment: Records of this species come from August and September (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Threat comments: Specific threats to this species have not been directly investigated. This species may be threatened by habitat loss and degradation by urban development. Three of the four localities for this species are located in the San Francisco bay area, which has seen considerable pressure from urbanization in the last several decades. It is estimated that over 40% of developed land is composed of pavement and structures (Connor et al. 2002), which precludes bee nesting. Records at these localities were collected from 1936 - 1957, before the region was heavily urbanized. It is unclear if the habitat required by this species still persists at these localities. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena grindeliae is a ground nesting species, and nests may be harmed by certain agricultural practices such as tilling, which can kill bees nesting close to the surface (Williams et al. 2010). Additionally, Andrena have been reported to have low reproductive output because of the short adult life span, and a low rate of brood cell provisioning (reviewed in Danforth et al. 2019). Other threats to bees generally include habitat loss or modification, climate change, pesticide use, exposure to pathogens from managed bee species, and competition with honey bees (Brown and Paxton 2009; Potts et al. 2010; Wojcik et al. 2018; Grab et al. 2019; Raven and Wagner 2021). Threats Threats: Timing: Scope: Severity: Impact Score: 1. Residential & commercial development -> 1.1. Housing & urban areas 1. Residential & commercial development -> 1.2. Commercial & industrial areas 2. Agriculture & aquaculture -> 2.1. Annual & perennial non-timber crops -> 2.1.3. Agro-industry farming 7. Natural system modifications -> 7.1. Fire & fire suppression -> 7.1.1.Increase in fire frequency/intensity 7. Natural system modifications -> 7.1. Fire & fire suppression -> 7.1.2. Suppression in fire frequency/intensity 8. Invasive and other problematic species, genes, and diseases -> 8.1 Invasive non-native/alien species/diseases -> 8.1.2. Named species 9. Pollution -> 9.3 Agricultural and forestry effluents -> 9.3.3 Herbicides and Pesticides 11. Climate change & severe weather -> 11.1. Habitat shifting & alteration 11. Climate change & severe weather -> 11.2.Droughts 11. Climate change & severe weather -> 11.3.Temperature extremes Conservation Actions Conservation needs No known conservation actions are in place for this species. Protected/Managed area comment: There are no observations of this species from any federally protected land. Management comment: Specific conservation needs for this species have not been identified. Due to the importance of supporting wild bee populations for pollination services, general conservation practices are recommended including, restoring, creating, and preserving natural high-quality habitats to include suitable forage and nesting sites; limiting pesticide use on or near suitable habitat, particularly during the adult bee’s flight period; promoting farming and urban practices that increase pollinator-friendly plants in margin space; minimizing exposure of wild bees to diseases transferred from managed bees; and lastly, avoiding honey bee introduction to high-quality native bee habitat. Conservation Actions Needed 1. Land/water protection -> 1.2. Resource & habitat protection 2. Land/water management -> 2.3. Habitat & natural process restoration 4. Education & awareness -> 4.3. Awareness & communications 5. Law & policy -> 5.2. Policies and regulations Research needs Research need comment: More information is needed about the population status, population trend, existing threats, range limits, habitat, and ecology of this species. Surveys targeting this species are needed throughout its range to determine its persistence throughout its historic range. Research Needed 1. Research -> 1.2. Population size, distribution & trends 1.3. Life History and Ecology 1.5. Threats 1.6 Conservation actions 3. Monitoring -> 3.1. Population trends 3.4. Habitat trends Assessment Date of assessment (month-day-year): 7-24-2025 Assessors names (use * to indicate primary assessor, typically the participant with most experience/knowledge of the species): Saff Killingsworth Reviewer(s): Contributors(s): For a full list of the 162 institutions that contributed to the Chesshire et al. dataset, please see Chesshire et al. 2023, S1. Facilitator(s) and compiler(s): Paige R. Chesshire, Erica E. Fischer, Nicolas J. Dowdy, Terry L. Griswold, Alice C. Hughes, Michael C. Orr, John S. Ascher, Laura M. Guzman, Keng-Lou James Hung, Neil S. Cobb and Lindsie M. McCabe Red List Category and Criteria: Vulnerable B1abiii Justification: Andrena grindeliae is a solitary bee species known from just eight observations. It occurs in central California, from the San Francisco Bay area east to the Sierra Nevada range. Using all observations of the species the extent of occurrence (EOO) is 8,398 km2. This species is only known from four localities, so there is a low degree of confidence in the accuracy of the EOO. Additionally, the species has not been observed since 1973, so it is unclear if it is still extant throughout its known range. This species likely occurs in just four locations if each locality is impacted by threats independently. All four documented localities of this species are now medium intensity urban development or developed open space. The habitat conditions at the time of collections are not well understood. It is possible localities of this species are no longer habitat supportive to the species. This species may also be threatened by climate change and exposure to pesticides, which have been observed across its range. More information is needed to determine if this species is still extant, and to better understand its life history and the degree to which it is impacted by threats. Because this species is known from an extent of occurrence that is less than 20,000 km2, is known from just four locations, and has seen habitat loss due to urban development in its range, it is assessed as Vulnerable B1abiii. Rank reasons This species is a solitary bee species known from just 13 observations. It occurs in central California, from the San Francisco Bay area east to the Sierra Nevada range. Using all observations of the species the range extent is 8,398 km2. This species is only known from four localities, so there is a low degree of confidence in the accuracy of the EOO. Additionally, the species has not been observed since 1973, so it is unclear if it is still extant throughout its known range. All four documented localities of this species are now medium intensity urban development or developed open space. The habitat conditions at the time of collections are not well understood. It is possible localities of this species are no longer habitat supportive to the species. This species may also be threatened by climate change and exposure to pesticides, which have been observed across its range. More information is needed to determine if this species is still extant, and to better understand its life history and the degree to which it is impacted by threats. Because this species is known from a small range extent, is known from just four element occurrences overall, and none since 1973, and has seen habitat loss due to urban development in its range, it is assessed likely to be threatened with extinction at this time. NatureServe Specific Text (NOT OTHERWISE INCLUDED IN ABOVE TEXT): For Rank Calculator: 1. Element occurrences (using separation distance of 5,000 m): 0 1. Estimated Number of Element Occurrences Comments: There have been no element occurrences of this species recorded in the last 30 years (since 1995). Overall this species is known from four occurrences using a 5 km separation distance. 2. Population size: Unknown 3. Viability/Ecological integrity (choose one) 1. Number of occurrences with good viability/ecological integrity: Unknown 2. Percent of area occupied (For Species with Known AOO): N/A 4. Environmental Specificity: Unknown 1. Environmental specificity comments: The environmental specificity of this species is not known, but it may have specific habitat requirements that are not yet understood. 5. Intrinsic Vulnerability: B. Moderately vulnerable 1. Intrinsic vulnerability comments: Andrena have been reported to have low reproductive output because of the short adult life span, and a low rate of brood cell provisioning (reviewed in Danforth et al. 2019). 6. Trend 1. Short Term Trend: Unknown 2. Comments: Abundance estimates and population trends are not known for this species. 3. Long Term Trend: Unknown 4. Comments: Abundance estimates and population trends are not known for this species. For Biotics Global Element Characterization: 1. Habitat Unknown 2. Food Habits 1. Adult: nectarivore 2. Immature: nectarivore Literature References: Ascher, J.S.; Pickering, J. (2025). "Discover Life bee species guide and world checklist (Hymenoptera: Apoidea: Anthophila)". Retrieved July 24 2025. Brown, Mark J. F., and Robert J. Paxton. 2009. “The Conservation of Bees: A Global Perspective.” Apidologie 40 (3): 410–16. Cane, James H., and Byron G. Love. 2021. “Hygroscopic Larval Provisions of Bees Absorb Soil Water Vapor and Release Liquefied Nutrients.” Apidologie 52 (6): 1002–16. Cane, J. H. 1981. “Dufour’s Gland Secretion in the Cell Linings of Bees (Hymenoptera: Apoidea).” Journal of Chemical Ecology 7 (2): 403–10. Chesshire, Paige R., Erica E. Fischer, Nicolas J. Dowdy, Terry L. Griswold, Alice C. Hughes, Michael C. Orr, John S. Ascher, et al. 2023. “Completeness Analysis for over 3000 United States Bee Species Identifies Persistent Data Gap.” Ecography, February. https://doi.org/10.1111/ecog.06584. Connor, Edward F., John Hafernik, Jacqueline Levy, Vicki Lee Moore, and Jancy K. Rickman. 2002. “Insect Conservation in an Urban Biodiversity Hotspot: The San Francisco Bay Area.” Journal of Insect Conservation 6 (4): 247–59. Danforth, Bryan N., Robert L. Minckley, John L. Neff, and Frances Fawcett. 2019. The Solitary Bees: Biology, Evolution, Conservation. Princeton University Press. Grab, Heather, Michael G. Branstetter, Nolan Amon, Katherine R. Urban-Mead, Mia G. Park, Jason Gibbs, Eleanor J. Blitzer, Katja Poveda, Greg Loeb, and Bryan N. Danforth. 2019. “Agriculturally Dominated Landscapes Reduce Bee Phylogenetic Diversity and Pollination Services.” Science 363 (6424): 282–84. Michener, Charles Duncan. 2007. The Bees of the World. Vol. 1. JHU Press. Potts, Simon G., Jacobus C. Biesmeijer, Claire Kremen, Peter Neumann, Oliver Schweiger, and William E. Kunin. 2010. “Global Pollinator Declines: Trends, Impacts and Drivers.” Trends in Ecology & Evolution 25 (6): 345–53. Raven, Peter H., and David L. Wagner. 2021. “Agricultural Intensification and Climate Change Are Rapidly Decreasing Insect Biodiversity.” Proceedings of the National Academy of Sciences of the United States of America 118 (2). https://doi.org/10.1073/pnas.2002548117. Rousseau, Josée S., S. Hollis Woodard, Sarina Jepsen, Brianne Du Clos, Alison Johnston, Bryan N. Danforth, and Amanda D. Rodewald. 2024. “Advancing Bee Conservation in the US: Gaps and Opportunities in Data Collection and Reporting.” Frontiers in Ecology and Evolution 12. https://doi.org/10.3389/fevo.2024.1346795. Williams, A. Park, B. I. Cook, and S. E. Smerdon. 2022. “Rapid Intensification of the Emerging Southwestern North American Megadrought in 2020–2021.” Nature Climate Change 12 (3): 232–34. Williams, N. M., Elizabeth E. Crone, T’ai H. Roulston, Robert L. Minckley, Laurence Packer, and Simon G. Potts. 2010. “Ecological and Life-History Traits Predict Bee Species Responses to Environmental Disturbances.” Biological Conservation 143 (10): 2280–91. Wojcik, Victoria A., Lora A. Morandin, Laurie Davies Adams, and Kelly E. Rourke. 2018. “Floral Resource Competition Between Honey Bees and Wild Bees: Is There Clear Evidence and Can We Guide Management and Conservation?” Environmental Entomology 47 (4): 822–33.

Conservation needs No known conservation actions are in place for this species. Protected/Managed area comment: There are no observations of this species from any federally protected land. Management comment: Specific conservation needs for this species have not been identified. Due to the importance of supporting wild bee populations for pollination services, general conservation practices are recommended including, restoring, creating, and preserving natural high-quality habitats to include suitable forage and nesting sites; limiting pesticide use on or near suitable habitat, particularly during the adult bee’s flight period; promoting farming and urban practices that increase pollinator-friendly plants in margin space; minimizing exposure of wild bees to diseases transferred from managed bees; and lastly, avoiding honey bee introduction to high-quality native bee habitat.

Research need comment: More information is needed about the population status, population trend, existing threats, range limits, habitat, and ecology of this species. Surveys targeting this species are needed throughout its range to determine its persistence throughout its historic range.

The male of this species is not known.