Both managed and wild bee species are in decline, making it more important than ever to understand the factors affecting bee health1. Luckily, many high-value crops, such as cucurbits (squash and pumpkins), are actually pollinated very effectively by wild bee species, which provide free pollination services2.

Cucurbits are visited by a variety of wild bees, such as bumblebees, honey bees, sweat bees, and squash bees3. Squash bees are an incredibly effective specialist pollinator of cucurbit plants, but little is known about their health status, particularly in their nests which can be hard to find. This is because they are solitary ground-nesters, where each female digs her own nest underground and the only clue to its presence is a small mound of dirt around the pencil-width entrance tunnel.

The Lopez-Uribe Lab at Penn State is working on a project to understand how landscape factors, pathogens, heat stress and beneficial microbes affect the health of the squash bee, Eucera (Peponapis) pruinosa. We are excavating nests to collect data on the pollen quality and microbial communities in these nests.


How to identify squash bee nests

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Squash bees are active from July to September and tend to make their nests in patches of exposed ground on the edges of cucurbit fields, although they are sometimes found directly underneath the plants themselves. Even though each female makes her own nest, females tend to nest near each other in an aggregation. The nests are easiest to find in the early morning when the bees are active. You’ll often hear them before you see them! Here are several pictures of nesting aggregations and sites that will help you to locate and identify the nests.

1. Squash bee nests are usually located on the edge of the Cucurbita crop in groupings called nesting aggregations.



2. Each nest tunnel is about the width of a pencil and surrounded by a dirt mound left from tunnel excavation.

3. Bees are active in the early morning from sunrise to late morning, about when the flowers close.


Questions about this research?

Please contact Kristen Brochu (



  1. Potts, S.G., J.C. Biesmeijer, C. Kremen, P. Neumann, O. Schweiger, and W.E. Kunin 2010. Global pollinator declines: trends, impacts and drivers. Trends in Ecology and Evolution, 25(6): 345-353.
  2. Garibaldi, L.A., I. Steffan-Dewenter, R. Winfree, M.A. Aizen, R. Bommarco, A. Cunningham, C. Kremen, L.G. Carvalheiro, L.D. Harder, O. Afik, I. Bartomeus, F. Benjamin, V. Boreaux, D. Cariveau, N.P. Chacoff, J.H. Dudenhoffer, B.M. Freitas, J. Ghazouk, S. Greenleaf, J. Hipolito, A. Holzchuh, B. Howlett, R. Isaacs, S.K. Javorek, C.M. Kennedy, K. M. Krewenka, S. Krishnan, Y. Mandelik, M.M. Mayfield, I. Motzke, T. Munyuli, B.A. Nault, M. Otieno, J. Petersen, G. Pisanty, S.G. Potts, R. Rader, T.H. Ricketts, M. Rundlof, C.L. Seymour, C. Schuepp, H. Szentgyorgyi, H. Taki, T. Tscharntke, C.H. Vergara, B.F. Viana,T.C. Wanger, C. Westphal, N. Williams, and A.M. Klein. 2013. Wild Pollinators Enhance Fruit Set of Crops Regardless of Honey Bee Abundance. Science, 339: 1608-1611.
  3. Meléndez-Ramirez, V., S. Magaña-Rueda, V. Parra-Tabla, R. Ayala, J. Navarro. 2002. Diversity of native bee visitors of cucurbit crops (Cucurbitaceae) in Yucatán, México. Journal of Insect Conservation, 6(3): 135-147.