Cities are accidentally becoming pollinator refuges. While industrial agriculture creates flowering deserts, urban balconies, rooftop gardens, and community plots are supporting surprising bee diversity. Research shows some cities harbor more native bee species than surrounding farmland. We explore why concrete jungles are working for pollinators, which species are thriving in cities, and how anyone—even without a yard—can create powerful pollinator habitat in just 10 square feet. From Chicago high-rises to San Francisco fire escapes, discover why your balcony might be more valuable to native bees than a thousand acres of corn.

www.secretpollinators.com

KEY SOURCES

Urban bee diversity

• Baldock, K. C. R., Goddard, M. A., Hicks, D. M., et al. (2015). Where is the UK's pollinator biodiversity? The importance of urban areas for flower-visiting insects. Proceedings of the Royal Society B, 282(1803): 20142849. DOI: 10.1098/rspb.2014.2849
• Baldock, K. C. R., Goddard, M. A., Hicks, D. M., et al. (2019). A systems approach reveals urban pollinator hotspots and conservation opportunities. Nature Ecology & Evolution, 3, 363–373. DOI: 10.1038/s41559-018-0769-y — allotments and community gardens identified as the strongest urban pollinator hotspots.
• Hall, D. M., Camilo, G. R., Tonietto, R. K., et al. (2017). The city as a refuge for insect pollinators. Conservation Biology, 31(1), 24–29. DOI: 10.1111/cobi.12840
• Theodorou, P., Radzevičiūtė, R., Settele, J., et al. (2020). Urban areas as hotspots for bees and pollinators but not for butterflies. Nature Communications, 11, 576. DOI: 10.1038/s41467-020-14496-6
• Normandin, É., Vereecken, N. J., Buddle, C. M., & Fournier, V. (2017). Taxonomic and functional trait diversity of wild bees in different urban settings. PeerJ, 5: e3051. DOI: 10.7717/peerj.3051 — 200 species across 46 sites in Montreal and Quebec City; community gardens carried high functional trait diversity.

The counter-evidence (worth acknowledging on air)

• Fischer, L. K., Eichfeld, J., Kowarik, I., & Buchholz, S. (2016). Disentangling urban habitat and matrix effects on wild bee species. PeerJ, 4: e2729.
• Buchholz, S., Gathof, A. K., Grossmann, A. J., Kowarik, I., & Fischer, L. K. (2020). Wild bees in urban grasslands: Urbanisation, functional diversity and species traits. Landscape and Urban Planning, 196, 103731. DOI: 10.1016/j.landurbplan.2019.103731
• Kühn, E., et al. (2023). The degree of urbanisation reduces wild bee and butterfly diversity and alters the patterns of flower-visitation in urban dry grasslands. Scientific Reports, 13, 2702. DOI: 10.1038/s41598-023-29275-8 — impervious surface cover negatively affected bee richness; flowering plant richness and ground-nesting resources positively affected it.

Berlin community gardens

• Egerer, M., Fairbairn, M., et al. Bee discovery suggests the importance of urban gardens in a changing world. Renewable Agriculture and Food Systems. — 18 community gardens across Berlin; 26 genera and 102 species documented.

Foraging range and body size

• Greenleaf, S. S., Williams, N. M., Winfree, R., & Kremen, C. (2007). Bee foraging ranges and their relationship to body size. Oecologia, 153(3), 589–596. DOI: 10.1007/s00442-007-0752-9 — 96 records across 62 species; nonlinear relationship between intertegular span and foraging distance.
• Gathmann, A., & Tscharntke, T. (2002). Foraging ranges of solitary bees. Journal of Animal Ecology, 71(5), 757–764.
• Wright, I. R., Roberts, S. P. M., & Collins, B. E. (2015). Evidence of forage distance limitations for small bees. European Journal of Entomology, 112(2), 303–310. — probability of observing a small bee (<1.5 mm IT span) dropped to 10% at 250–370 m from nesting habitat.

Agricultural intensification and floral resources

• Timberlake, T. P., Vaughan, I. P., & Memmott, J. (2019). Phenology of farmland floral resources reveals seasonal gaps in nectar availability for bumblebees. Journal of Applied Ecology, 56(7), 1585–1596. DOI: 10.1111/1365-2664.13403
• Kennedy, C. M., Lonsdorf, E., Neel, M. C., et al. (2013). A global quantitative synthesis of local and landscape effects on wild bee pollinators in agroecosystems. Ecology Letters, 16(5), 584–599.

Urban beekeeping caution

• MacInnis, G., Normandin, É., & Ziter, C. D. (2023). Decline in wild bee species richness associated with honey bee abundance in an urban ecosystem. PeerJ, 11: e14699.

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