Impacts and Recovery Status of Wild Bees

Mid-season report: Impacts and recovery status of wild bee communities following a catastrophic flood

Jessica Mullins
University of Colorado Museum of Natural History (CUMNH) Entomology Section, 265 UCB, University of Colorado, Boulder, CO 80309 e-mail:

The Earth’s climate is rapidly changing, which has led to more frequent extreme weather events, such as flooding. Extreme weather events significantly impact biological communities and the predicted increase in frequency and severity of these large disturbance events could prevent these systems and the ecosystem services they provide from full recovery, resulting in both long- and short- term impacts that we are only beginning to understand. The flood that hit Colorado’s Front Range in the fall of 2013 provides a unique opportunity to study the impacts of flooding on an important group of organisms, wild bees. Bees are essential pollinators in wild, urban, and agricultural ecosystems, and they can also play a vital role in plant colonization and reestablishment through pollination, an essential process following large disturbance events such as a flood.

This February, we were awarded funding from Lois Webster Fund to conduct field surveys and process data to investigate the recovery status of wild bee communities along the St. Vrain Greenway in Longmont, CO. These communities were severely impacted by the 2013 flood (based on previous data provided in the original grant application). So far this year, we have spent 113 hours in the field collecting data and 283 hours processing the samples. We have reserved the 150 hours of funding to hire an assistant in the fall semester, pending the status of COVID-19 safety measures.

As described in my project proposal, we are sampling a set of 11 sites, that were previously sampled pre-flood (2012) and post-flood (2014), 10 times between April and October using the same collecting methods utilized in 2012 and 2014. I will compare the data collected this year to data collected from these same sites previously. This season’s sampling has gone very well, we initially started sampling the Greenway on April 5, but due to the late winter, few plants were in bloom and few bees were found. Sampling conditions were prime in late April, and the first complete sampling round started on April 27. To date, we have completed six of the ten sampling rounds for each of the 11 sites. Following each collection round, each specimen is curated for vouchering in the CUMNH Entomology Collection. This process includes four main steps: pinning, labeling, identification, and databasing. So far in 2020 we have collected 3,579 bees. See Table 1 on the following page for information on the progression of specimen preparation from the 2020 field season. Figure 1 is a photo of a drawer with successfully curated specimens collected in Round 3. Thus far, we have 8 full drawers of specimens.

In addition to the above, so far in our field collections we have observed two notable bees: The Western Bumble Bee, Bombus occidentalis, and the Eastern Carpenter Bee, Xylocopa virginica texanus. The Western Bumble Bee is experiencing record declines throughout its range, and we were pleased to see a queen of this species at our field site Lykin’s Gulch on May 13, 2020 (see Figure 2). We did not collect this queen due to the species current state of decline and queens are responsible for producing hundreds of workers and males. This queen’s occurrence was documented by the photograph in Figure 2 on both iNaturalist and Bumble Bee Watch. Should we encounter a non-reproductive worker or male of this species, we will collect a specimen that will be a DNA voucher for ongoing nationwide research on this species.

Finding the Eastern Carpenter Bee, pictured in Figure 3, in Colorado was another interesting discovery, as its occurrence here suggests a significant range expansion or a repeated introduction. Currently there are no voucher specimens of this species collected west of Davis County Texas; although there has been one iNaturalist observation of the species in Boise, Idaho1, but no voucher was taken. The CUMNH Entomology Collection has one female specimen of this species collected by Diane Wilson in Jefferson County Colorado in 2011. The data from this specimen has not yet been published and range expansion of this species is yet to be explored. It is unclear if there is a growing population in Colorado’s Front Range or if these recent specimens simply represent repeated independent introductions to the area that do not survive the winter months.

With more half of the field season complete and the rate at which we are able toprocess specimens and data, we are confident our collections will be completed by late September and we will have a report of our findings prepared by the November deadline. We are grateful for the opportunity to conduct this important research and the support provided by the Lois Webster Fund. This research will provide data that will be critical for understanding how wild bee communities respond to extreme flooding events.

Special Thank You

Jessica wanted to especially thank Virginia Scott, the CU Museum of Natural History Entomology Collection Manager and bee expert. Scott authored Bees of Colorado. This project would not exist without her fortuitous sampling in 2012 before the flood, again in 2014 and I could not have done this year’s sampling so seamlessly without her help.

Additional Photos Provided by Jessica

Additional Resources

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