Maryland Grows

We hear a lot about pollinators these days, but most of the attention appears to always go to one group of them: bees. However, the diversity of pollinators expands way beyond this one group of insects, as we discussed in a previous post. In today’s post, I want to bring the spotlight to one of those non-bee pollinators, which I always feel stay in the background of our pollinator discussions and are massively underappreciated, despite their important role in our ecosystems. Come with me to give hoverflies the recognition they deserve.

What are hoverflies?

With over 100 species in Maryland, hoverflies (sometimes also called flower flies, or simply syrphids) are a group of flies that belong to a family of insects called Syrphidae. They are called hoverflies because they are very good fliers, able to quickly change directions or maintain their flying positions in very impressive ways. While their larval stages can have a huge variety of nutritional needs (some of which make them great biological control agents of pests), a very large number of the species are strongly associated with flowers as adults. In fact, the females require nectar and pollen consumption for their ovary development, making them depend strongly on floral resources for reproduction. For this reason, they act as important pollinators of many wild plants and crops, especially in temperate climates. Although not fully recognized by the general public, pollinating hoverflies have been shown to contribute globally to the pollination of over 70% of crops globally and about the same percentage of European wildflowers (few studies have evaluated the latter in North America)! You can learn more about this in this recent publication.

Ecology and biology of hoverflies

I hope that you’re now starting to get excited about these little creatures. Before you run outside to try to catch a glimpse of them, let me tell you some more about their lives, so you can continue to be amazed at what they do and why I am on a “pollinator recognition” mission for them.

As I was saying before, a vast majority of hoverflies are strongly associated with flowers. This makes them potentially important pollinators, and this is indeed true for many of them. However, there’s another reason why they are so important: their ecology. In fact, hoverflies have migratory or at least long dispersal behavior. This means that they have great potential for long-distance dispersal of pollen, and thus can contribute strongly to the pollination of plants that may be spatially far away from each other. Thinking about pollination and its role in plant reproduction, such long-distance pollen dispersal can be key in the reproduction of isolated plant populations, and even in increasing and maintaining genetic diversity in those populations. All of that tends to positively impact the ability of those plants to maintain their populations, making hoverflies key actors in sustaining the diversity of many wild plant species.

And also, because I really want to make an impression on you 😊, know that when I talk about hoverfly migration, I am talking about migration patterns that can in some cases be equivalent to those of more “famous” insects, such as monarchs. Some studies have shown some hoverfly species migrate thousands of miles, following the seasons. Although this is relatively well-studied in Europe, we know that similar migration patterns also occur in other parts of the globe, including North America. And as a fun fact, in our research group at UMD, we believe that we once observed and sampled a wave of migration of hoverflies right here, while studying pollination interactions in the endangered serpentine grasslands of Maryland.

How to recognize them?

Perhaps a reason why hoverflies are underrecognized is that many of their species display impressive body mimics of other species, many of which people tend to be afraid of because of their stingers. For example, some of the most common hoverflies in our area display yellow and black stripes, tricking us (and potential predators) into believing they are in fact wasps or bees. This is a strategy that protects them from predation but also requires us to be more attentive when we are trying to find them.

Despite this, there are some simple ways to recognize their trick. Because they are flies, hoverflies have characteristics that differentiate them clearly from other groups of insects, such as wasps. One of the main traits to look for when trying to figure out if we are facing a hoverfly (vs. a wasp, for example), is looking at their wings. Unlike bees and wasps, flies have only one pair of wings, which at rest they usually extend perpendicularly to their body, which makes them look like a plane or a “T”. Wasps and bees, on the other hand, typically don’t do this, and they fold their two pairs of wings flat over their abdomen while they are at rest.

Another way to tell them apart from most other wasps and bees is their heads (this may be also useful when the wing trait is not easy to see). In fact, flies generally have VERY large eyes (just think about any fly costume 😉). Hoverflies are no exception! They also have large eyes that cover a very large part of their heads, as well as very short antennae. On the other hand, bees and wasps, usually have much much longer antennae that extend way beyond their heads.

Ready to go out and find some of them? Remember that you can always check out iNaturalist to help you out with identifications! Good luck!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!