Spring is well-established and many flowers have already started to bloom. In my garden, I have seen several sizes and shapes of insects visiting flowers, going from small flower flies to butterflies, to very tiny and shiny, fuzzy large, and very large bees. And with all these flying organisms starting to come around us, I thought today would be a really good time to introduce you to some really cool bees that are very common in our area: the leaf-cutter bees!
What are leaf-cutter bees?
As its name suggests, these are solitary bees known to cut leaves (now you may be thinking, “duh, I could have guessed that without a blog post”, but bear with me!). These bees belong to a very large family of bees called Megachilidae, which is present on all continents except Antarctica and well-represented in our region.
Like most solitary bees, the female of leaf-cutter bees builds nests with small brood cells, in each of which a food provision is left and one egg laid. And this is where the “leaf-cutter” name comes from. When building their nests, many of these females line their brood cells with specific materials, in particular plant tissues. In fact, many of the species are known to cut leaves and/or petals to line their nests, using them to stabilize the brood cells, and likely to provide protection to the larva and the food provisions. In a fascinating way, it is suspected that these bees are able to exploit the antimicrobial effects of certain compounds present in these flowers and leaves, indirectly using them to protect their offspring until they finish their development in the nests.
If you ever saw neat and relatively large holes that seem to suddenly pop up on certain plants in your green spaces, it is very likely that they were made by some of these bees that may be nesting close to you! If you keep an eye out on those plants, it is very likely that you will end up seeing these busy bees carefully cutting, then rolling, and finally flying away with the neat plant circles!
Looking out my window, as the ground is covered with snow and I am getting ready for another snowstorm coming tonight, it seems ironic that I have been spending many hours these days ordering seeds and planning my garden. While I am thankful that the winter brings some rest to the soil in my garden, planning this season brings me happy memories of the scents and buzzes in my yard during the growing days… which reminds me that I should also plan for my little buzzing pollinator friends when I plan what to grow this season. In today’s blog, I want to chat about how we can plan for many types of pollinators, with a special focus on planning for specialists and not just for generalist pollinators.
Specialist pollinators – never heard of them?
As we mentioned in a previous post, pollinators visit plants to feed on nectar and/or to collect pollen to feed themselves or their offspring. However, pollen is not just there for pollinators to feed on; pollen is central to plant reproduction, so plants tend to make it both attractive to pollinators but hard to digest. For this reason, and in order to be able to properly digest the pollen, pollinators are often specialized in their pollen choices. This is because being able to digest the compounds that plants add to their pollen to make them hard to eat requires some level of adaptation, which often involves a trade-off with the ability to eat anything. There are, of course, many levels of specialization, and, while many pollinators feed on many plant families, others are more specialized than that, and feed on only specific plant genera or even species! For us gardeners, this means that if we want to support many different pollinators, we need to make sure that we are also providing for those very specialized pollinators as well!
Luckily for us, the floral choices and pollen specialization is known to some extent for Maryland and Eastern USA bees (see this site to learn more). For this reason, we know that many specialized bees in our region are also rare or uncommon… another reason to try to provide resources for them!
Who are pollen specialists in our region?
Many known pollen specialist bees in our region belong to bee genera Andrena, Colletes, Osmia, and Melissodes, which have many species considered rare or uncommon in Maryland and Mid-Atlantic.
The sun and the warm(er) days are back! Oh gosh, it felt like forever! And now, of course, I am feeling like I have to get out there and start doing stuff outdoors! And because I love the little creatures, one of the things I want to do is make sure that this year my garden becomes a pollinator’s paradise. If you are in the same boat as me, come along and let’s talk about how to make our gardens inviting to pollinators!
Like us, pollinators need food and a place to live
We hear a lot about pollinators and the plants we can grow to help them. And it is true, to live and thrive pollinators need food, and that food usually comes from plants. Indeed, to sustain pollinators, it is key that we provide food for them. However, we often forget that they need something else to thrive: a place to live! And because there are SO MANY types of pollinators, let’s for this one time focus on only one group, the bees!
Even though many people think only of honeybees when we talk about bees, most bees do not live in colonies like honeybees do, and are in fact solitary. Solitary bees are indeed the vast majority of bees. In Maryland we have about 400 different species of them, going from tiny to very large. Check out this awesome free book about bees from our region.
Unlike honeybees, each of these wild bee species has different nesting requirements, and many of them will nest readily close to our houses if they find the right conditions. Here I will give you some pointers on how to create those conditions to not only attract bees with flowers, but also help them live close to your garden.
How do wild bees live?
Unlike honeybees which lay eggs throughout the growing season, wild bees usually lay eggs only at certain times of the year, meaning that their life cycle is different from that of honeybees. Most solitary bees in fact lay eggs at only one point throughout the growing season (for example, only in the spring, summer, or fall).
Whenever they are ready to lay eggs, bee mothers start looking for a place to nest, and it is only during this time that they will be building their nests. Once the eggs are laid, the mother leaves and those eggs stay in the nest along with some food (usually pollen mixed with some nectar). After hatching, the larvae eat the food the mother left for them, and they continue feeding and growing until they are ready to leave the nest as adults, usually the following year. This means that for most bees there is no or very little maternal care of the offspring, and most of the time spent in a bee’s life is as a larva, growing and getting ready for the “outside” world.
Where do wild bees live and how can I help them nest?
Wild bees have a variety of nesting preferences. While some nest in the ground, others dig holes in wood, use already-existing cavities, or parasitize other bees’ nests by consuming the reserves of their hosts (yeah, bees can be sneaky like that!). Understanding this is important, because depending on the resources we provide for nesting, different species will be attracted to our gardens.
Keep some ground undisturbed – Ground-nesting bees
If you would like to support these bees in your garden, you can make sure to leave some of your garden soil undisturbed or bare. If you do this, you will realize that many bees will be attracted to that section, and if you pay attention, you will realize that many are actually coming in and out of the ground! These are your ground-nesting bees! In Maryland, some ground-nesting bees that you may have seen visiting flowers are the small and shiny green sweat bees.
Leave some wood in your yard – Carpenter bees
In our region, these bees are represented by the very large shiny carpenter bees of the genus Xylocopa. These bees have strong mandibles they use to excavate soft wood in order to build their nests inside. If you would like to attract these bees to your garden, make sure to leave relatively large branches and logs available for them to nest in. For this, you can turn a corner of your yard a bit wilder, and at the same time, leave branches there to allow other beneficial organisms to establish in your garden.
Bee hotels! – Cavity-nesting bees
Unlike carpenter or ground-nesting bees, these bees do not create the cavities, but rather use those that already exist. This is the group of bees that is attracted to those cute bee hotels one can build or buy. A natural option for supporting these bees is also by not cutting down to the ground the hollow stems of some plants at the end of the season. Many bees nest within these stems, and will die if they are chopped-off during the winter. Species in this group of bees nest in the spring, summer, or fall. For this reason, if one wanted to use bee hotels to attract these bees, one should establish them early in the spring.
There are a multitude of types of bee hotels, with some involving little tubes that can be removed, holes drilled into wood, a collection of small hollow twigs and branches, paper rolls, etc. Check out this site to see many options. Independently of the type of bee hotel you want to use, something important is to make sure that you keep the cavities clean for the bees to develop in healthy conditions. Failing to do so may actually harm the bees we are trying to support, because they may continue to be attracted to the nesting site we are providing but may eventually become sick and die because the place was unhealthy.
Now it’s our turn!
I really love watching bees build their nests, independently of what they look like. Maybe I’m just nosy, or maybe this is really why I’m a biologist, but that peek into these little animals’ lives makes me feel connected to them and keeps me in awe at how wonderfully diverse and fascinating life can be. When you are planning your garden this year, I invite you to consider the flowers for your bees, but also count in where you plan to have them live! And then, later in the season, go check those places out; I’m sure you won’t be disappointed!
By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.
New! Anahí is starting 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!