Leafcutter Bees: Gentle Summer Garden Pollinators

Leafcutter Bees: Gentle Summer Garden Pollinators
Leafcutter bees to the rescue!

Many gardeners wish they could raise honeybees to ensure their garden’s pollination but raising honeybees takes a lot of time, money and training. Some communities don’t allow honey beekeeping because of safety concerns. The problems facing honeybee populations are well known but honeybees are not the only bees suffering due to habitat loss, pollution, disease, and climate change.

Leafcutter bees are alternatives to honey bees that gardeners can rely on and they are better pollinators, easier to raise, cheaper, and most importantly, safer for children.

What are Leafcutter Bees?
Leafcutters bees are solitary bees, which means each female is fertile and she does all of the chores to raise her young. There are many different species of leafcutter bees and some species build their individual nests inside of pre-made nesting holes while others build nests underground.

Leafcutter bees get their name from their habit of building protective cocoons for their young out of pieces of leaves. The mother leafcutter bee builds a leafy cocoon for each egg and provisions the egg with all the food it will need to eat to grow into an adult bee. Sometimes a leafcutter bee will gather flower petals instead of leaves and cocoons made from petals are beautiful.

A reusable wooden nesting tray for leafcutter bees; note rose petal coccoons bottom right.

Alfalfa Leafcutter Bees: Perfect for Farms & Gardens
One species of leafcutter bee stands out from the rest and it has many features that makes it a perfect bee for pollinating summer gardens and farms. Even though it’s a solitary bee, the alfalfa leafcutter bee (Megachile rotundata) likes company because they build their nests near one another. There is no sharing of nests, however. Gregarious, or neighborly bees are prefect for farms where many bees are needed to pollinate the fields.

A farmer's batch of leafcutter cocoons, many have open holes from bees emerging
Alfalfa leafcutter bees became heroes in the 1940’s when they saved the declining alfalfa seed industry. A high protein feed source for livestock, the loss of this crop was threatening a major livestock nutrient. Hay mixes and seed production decreased when pollinating bees lost their habitats to changes in agriculture and residential growth. Farmers turned to leafcutter bees because these bees are 15 times better pollinators of alfalfa than honey bees. Today, the alfalfa leafcutter is still used extensively to pollinate alfalfa and other crops. Although they are named after alfalfa, we simply call these bees leafcutter bees because they are generalists that love to pollinate flowers of all types near their bee house.

We cannot easily raise bee species that nest underground but we can easily raise and, as needed, move hole-nesting bees. Alfalfa leafcutter bees nest in 6mm nesting holes and we’ve been raising them for decades and know very well how to care for them.

Easy to Raise & Better Pollinators
The female leafcutter bee carries pollen on the underside of her hairy abdomen, and then scrapes the pollen off within her individual nesting hole. Pollen is carried loose and dry on her hair and it falls off easily as she moves among blossoms. Leafcutter bees have a short flying range of only 300 feet from their bee house and you can be sure they are busy at work nearby in your garden or field. Leafcutter bees are active in the warm summer months and they are perfect for pollinating squash, melons, cucumbers, peas and other summer vegetables and fruits.
Leafcutter bees carry pollen dry and loose on their hairy bellies.

Raising leafcutter bees is easy and doesn’t require much time or training. The steps are simple: set up the house (like hanging a bird house), set out nesting holes and leafcutter cocoons, wait and watch, and bring filled nesting materials inside in early fall. There is no need for protective gear, since the bees overwinter in leafy cocoons and they rarely sting, nor expensive equipment to rent or buy because there is no honey to manage (only social honey bees make honey). Watch this video from Crown Bees that explains how setting up leafcutter bees is easy and takes only a few minutes.

Setting up leafcutter bees is easy and takes only a few moments

In terms of time, plan about 15 minutes to select a location and set up your house. Warning! When your bees emerge and start pollinating, you’ll have to set aside time to observe them come and go. Time flies as you watch them laying eggs for next season’s bees!
In late August, after bee activity stops, store filled nesting holes (open ends up) in an unheated garage or shed that is dry and secure. Placing filled nesting holes in a fine mesh bag will protect them from pests. Overwinter bee larvae in the nesting holes until next spring. In just 1 to 2 hours a year of your time, you’ll get a healthy garden yield and amazing garden companions. A bonus is that you’ll typically increase your bee cocoons from when you started. You can share your extra leafcutter cocoons with local family or friends and help them learn about how to raise these gentle safe bees.

Leafcutter Bees are Gentle
These solitary female bees can’t gather pollen and nectar, lay eggs, cut and gather leaves, and defend her nesting hole. Instead, she may be shy and wait for you to leave the vicinity of her nesting house or simply fly around you. Leafcutter bees are extremely gentle and allow you to approach their bee house without fear of being stung.
Although leafcutter bees have stingers, they will only sting if their life is threatened. Male bees do not have stingers and stings are only caused when the female bee thinks it is being squished. Even if you are unfortunate enough to be stung, the effects are generally no worse than a mosquito bite.
What’s Inside of a Leafcutter Bee’s Nest?
Leafcutter bees do not create holes or damage structures to make holes. North America is home to several native leafcutter bee species. Alfalfa leafcutter bees prefer nesting holes that are 6mm in diameter, some native North American leafcutter bees are larger and prefer 8 mm holes. There are even leafcutter bee species that nest underground!

A female leafcutter bee gathering a leaf to protect her eggs.

The female leafcutter bee uses her large jaws to make small, oval cuts in thin-walled leaves that she can then curl in half and carry back to her nesting site. The leaf texture must be just right, not too thick or spiny, similar to rose, hosta, and lilac. Some leafcutter bee raisers have not been able to find evidence of cut leaves, even with hundreds of leafcutter bees in their bee home. You may want to plant peas for leafcutter bees since peas grow quickly, are easy to grow, and can be used as sacrificial leaves for the bees.

The mother leafcutter bee builds a protective leafy cocoon for each egg. She builds the leafy cocoons by starting at the back of the nesting hole. The interior end of the leafcutter cocoon is round and the exterior end is flat. Inside the cocoon is a pollen loaf, which is a mix of nectar and pollen, and a single leafcutter egg. Each leaf cocoon is right next to each other and sometimes when you harvest the cocoons they are stuck to one another. When the female bee is done building cocoons in the nesting hole, she adds an extra thick layer of leaf bits at the opening. She may claim and fill a few different nesting holes but she works on them one at a time.

The leafcutter egg might hatch right away or it might go into hibernation for the fall and winter. If the summer season is long enough, the larva has time to develop quickly into an adult. These new adult bees are called second generation bees and they go right back out to mate and start the cycle again. When the second generation bees emerge you’ll see a large hole in the front flat end of the leaf cocoon. Extra generation of bees means a leafcutter bee’s pollination season is long, it’s just another reason why they are great summer garden pollinators.

The BeeHaven leafcutter bee house is an easy way to get started.

Keys to Successfully Raise Leafcutter Bees
1. Place your house with nesting material facing the early morning sun. The warmth wakes your bees earlier to start pollinating. Follow the setup instructions.

2. Leafcutter bees build protective cocoons out of leaves. If she can’t find the right type of leaf to cut and carry, she’ll leave your yard and set up her home elsewhere. This is the number one problem people face. Try planting peas for these superior pollinating bees.
3. After bee activity stops, store filled nesting holes (open ends facing up) in an unheated garage or shed that is dry and secure. Overwinter bee larvae in the nesting holes until next spring. Leaving them outdoors exposes them to pests and weather elements.
4. Harvest leafcutter cocoons in the early spring. You will remove pests and diseases as you harvest cocoons. You will also be able to take inventory of your leafcutter cocoon stock after harvesting them.
5. Leafcutter bees need to be incubated in order to develop into adult bees. At room temperature, it takes the cocoons about 6 weeks to develop and it will take less time in a warmer temperature. Leafcutter bees that are purchased from Crown Bees arrive incubated and ready to emerge from their cocoons.
Description of Leafcutter Bees
1. Alfalfa leafcutter bee females are black with pale yellow stripes on the abdomen and face. They are about 2/3 the size of a honey bee. Male alfalfa leafcutter bees are overall brighter in color and have green eyes and longer antennae.
2. In general, they emerge later in the summer when temperatures are in the 80°’s F (25°’s C). Plan the emergence of your leafcutter bees for when the temperatures are warm enough and your garden’s flowers are blooming.
3. The nesting range for these bees is about 300′ (100m) from their nest.

Content courtesy of Crown Bees

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