The Unexpected Diversity of Philadelphia’s Bees

While Philadelphia may not seem like an ideal habitat for wildlife, the city and county actually have a variety of green spaces, such as the John Heinz National Wildlife Refuge at Tinicum, the United States’ first urban wildlife refuge, to support plenty of different plant and animal species — including bees. But how many different kinds of bees call this city home? We reached out to Drexel University student and Academy co-op Liz Otruba to discuss what the bee population at the refuge really looks like. 

Tell us about yourself. 

I am an environmental science senior in the Biodiversity, Earth and Environmental Science Department at Drexel and work in the Entomology Department at the Academy of Natural Sciences of Drexel University. Last summer, I did a co-op with the Academy to survey the bee population at the refuge to see how many species were really there.  

What did you end up finding at the refuge? 

Aside from community scientist observations on iNaturalist and a bumble bee survey done five years ago, there’s no record of the full diversity of bee species that can be found at the refuge. We used three different collection methods to sample bees in the field and then sent the pinned specimens to experts at Penn State University who particularly specialize in identifying bees, especially the less common bee species, for them to verify my initial identifications.  

Megachile sculpturalis, Giant Resin Bee on Purple Loosestrife flower. Liz Otruba/ANS

After sampling different areas of John Heinz Wildlife Refuge from April to September of 2022, we ended up with about 2,500 bee specimens. So far, with our first batch of ID-ed bees we got back from Penn State, we found 56 bee species that occurred at the refuge. Of the 56 species we found, 16 of them are county records — that means that these species have not previously been recorded to occur in all of Philadelphia County. Once we get our second batch of bees back from Penn State, we might find even more new species! 

Tell us more about those 56 species — that’s a lot more than just honeybees and bumble bees.  

Honeybees and bumble bees are only eight of those 56 species! When people think of bees, yellow, fuzzy bees making honey in their hives seems to be the prevalent idea of what a bee is — but honeybees and bumble bees are actually quite unique compared to all other bee species. Honeybees are the only ones to make honey and live in hives, and many bees are much smaller than bumble bees.

Ceratina, Small Carpenter Bee on Fleabane flower. Liz Otruba/ANS

A majority of bees are not social (so they don’t have a queen) and make their nests underground or in rotting wood. Some of the most common bees we found at the refuge are smaller than a house fly and not yellow or fuzzy — Small Carpenter Bees, which are dark blue, and Sweat Bees, which are metallic, shiny green. There are even some bees that are completely red: Nomad Bees.

Why does this diversity matter? 

It’s really important to know what bee species are present in the refuge so we know what we have to protect. Bees (native ones in particular) play integral roles in supporting and sustaining a variety of other plants and animals in an ecosystem. However, bee populations are declining worldwide, so we have to know what exactly we are working to conserve.

For example, one of the new species we collected was the native Rose-mallow Bee, which exclusively pollinates and feeds on Hibiscus flowers. Now that we know Rose-mallow Bees are present, the refuge can ensure they’re supporting these bees by sustaining Hibiscus flowers across the marshes.  

These 43 bees are all different species and were all collected at Heinz in 2022. Liz Otruba/ANS

Visit Liz Otruba and learn all about local bees and her work at the John Heinz Refuge at this year’s Bug Fest!


  1. It would be wonderful to have more information about these bees, some of which I assume we can find in local gardens. Ideally we could use a top view and a side view of each, with its name. But even a list of the names would allow us to find other image, on iNaturalist, for example.

    1. Hi Nancy, this is a great idea, thanks for sharing! In the meantime, Liz will be at our upcoming Bug Fest this weekend and would love to answer any questions you have about this work!

    2. Hi Nancy! I am currently working on compiling all of the results of the monitoring project at John Heinz. Until that report is out, a good way to explore Philly bees on iNaturalist is to search the taxa ‘Anthophila’ with the location set to ‘Philadelphia’. Thank you for reading and your comment!

  2. It would be nice to mention that purple loosestrife is a non-native, extremely invasive plant. Posting a picture in this article with a bee on it makes people think that by planting it they might support bees, when in reality purple loosestrife takes away habitat and host plants for native insects. I would replace the picture with a native plant, there are plenty at John Heinz, or talk about the problem non-native species creates. So many people still plant purple loosestrife they buy from local nurseries.

    1. Hi Tyler, we totally appreciate your concern about invasive plants and encourage you to reach out to the John Heinz Refuge to see what efforts are being done to mitigate their growth!

    2. Hi Tyler, thank you very much for this comment! I believe John Heinz is in the process of removing and replacing the invasive Purple Loosestrife. I wanted to include a picture of the Giant Resin Bee here because there are no previous records of this bee occurring in Philadelphia. While the only picture I had of this bee was on Loosestrife, they also readily visit Mountain Mints along with many other pollinators!

      1. It is correct, we are removing and replacing Purple loostrife. We also have plenty of mountain mint in the refuge.

  3. If you go down the mowed “trail” that parallels the gravel road on the “train tracks” side of the refuge, and then turn toward the lagoon, there’s a path with a bench and look-out at the end. Last week I sat on the bench and watched ground-dwelling bees going in and out of the many small holes (pea to dime-sized). Their pollen baskets were packed.

    1. Hi Katherine! We also observed these so-called “Digger Bees” last year. It’s great to hear that these communities are still thriving!

  4. So we can assume that this is the current baseline for The Heinz Refuge, not all of Philadelphia County, which has additional habitats and potentially hosts even more species of bees.

    Of the bee species counted, how many are deemed native to our region vs introduced species?

    I agree that the picture of the purple loosestrife should include a label as invasive or cropped in a manner that the flower identity is not apparent. Too many people see a pretty flower and adult pollinators on it and then erroneously deem the invasive flower beneficial (see e.g. Buddleia davidii).

    1. Hi Marcus! Yes, it’s very likely there are more species to be found throughout the rest of Philadelphia County. It’s very exciting that so many species can be found in just this small section of the city and county!

      While I am still working through all the data, so far a large majority of the bees we collected are native to Pennsylvania. There are a few exotic species of Leafcutter Bees, as well as the European Honeybee.

  5. Forgive me if this is a ridiculous question; I’m not a scientist. When you say 2,500 specimens, does that mean captured and not released? What are the three collection methods used?

    1. Hi Marjorie, thank you very much for reading and your question! Yes, we did have to use lethal collection methods for this project. Many bees are hard to identify to species, or even genus, from just observing them in the wild. A microscope is needed to look at their small features.

      The first collection method was just an aerial net we would use to catch bees when they were visiting flowers, so we had records of what bees were visiting what flowers. The other 2 methods were for more prolonged collection, Bee Bowls and Blue Vane Traps. They both used fluorescent colors to attract bees. The Bee Bowls were almost like a to-go sauce container, and painted with fluorescent paint. They would be left out for about 5 hours on average. The Blue Vane Traps had 2 pieces of fluorescent blue plastic that would attract the bees to then enter a collection jug. These were left out continuously for an average of about a week.

      1. Imagine how it would be for humans, if Aliens were to be studying us.
        I am Not supportive of killing living things to “study a species”.

      2. So, with this research, will you ultimately be able to share a list of plants and/or whole habitats that we all could be planting in this area, to increase support for all of these beautiful creatures? I am a member of a beekeeping club in Delaware and want to do more with promoting wild pollinators and what each of us can be doing in our backyards to promote all of the wild pollinators.

        Thank you for this amazing article.

  6. This is great work Liz! I was wondering if there was a way to have citizen scientists record their bees in the City and send it to the Academy to make a city wide map and database to see where bee diversity is different, why, causes, and importance.

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