Leafcutter Bees

Gentle Summer Pollinators

The alfalfa leafcutter bee is a perfect pollinator of summer’s backyard gardens! A friendly, efficient, tireless pollinator, the alfalfa leafcutter bees became heroes in the 1940’s when they saved the declining alfalfa seed industry. Alfalfa is a high protein feed source for livestock and the loss of alfalfa 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. Alfalfa leafcutter 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. Alfalfa leafcutter bees (Megachile rotundata) are now naturalized across North America. Raising alfalfa leafcutter bees in agricultural fields has taught us how to raise other summer solitary hole-nesting bees.

****Alfalfa leafcutter bees are 15 times better pollinators of alfalfa than honey bees! #savethebees**** Click To Tweet

Easy to Raise & Better Pollinators

The leafcutter bee is an efficient pollinator for summer gardens and flowers. 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. Alfalfa leafcutter bees do not mind being hit on the head as the alfalfa flower’s keel is tripped open and this characteristic is what made them the darling of alfalfa fields. Although they are named after alfalfa, these bees are generalists that will visit many different kinds of flowers. 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.

Megachile Rotundata: Gentle and Neighborly

Leafcutters bees are solitary bees, which means each female is fertile and she does all of the chores to raise her young. These solitary female bees gather pollen and nectar, lay eggs, cut and gather leaves, and defend their nesting holes. Though their scientific name may sound intimidating (megachile rotundata), leafcutter bees are extremely gentle. They may allow you to approach their bee house without fear of being stung. Instead, she may be shy and wait for you to leave the vicinity of her nesting house or simply fly around you. Even though leafcutter bees are solitary, they like company because they build their nests near one another. There is no sharing of nests, however. Gregarious (neighborly) bees are perfect for farms where lots of bees are needed to pollinate the fields.

Although leafcutter bees have stingers, they will only sting if their life is threatened. More times than not, stings are caused by being caught in clothing and the 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 a Leafcutter Bee’s Nest?

Leafcutter bees are hole-nesting bees that lay their eggs in existing holes. They do not create holes or damage structures to make holes. Each female bee is solitary and she chooses a nesting hole that she claims as her own. There are many species of leafcutter bees across the world and 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!

The female leafcutter bee uses her large jaws to make small, near-circular 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 and the bees like to use leaves 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. Sometimes leafcutter bees use flower petals to build cocoons and these cocoons are special and beautiful.

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. The second generation bees emerge and you’ll see a large hole in the front flat end of the leaf cocoon.

There can be more than one extra generation of bees and this makes the leafcutter bee’s pollination season long, it’s just another reason why they are great summer garden pollinators.

How To Get Started Raising Leafcutter Bees

If you are interested in keeping leafcutter bees in your yard or garden, you can get started with very little time and money. You will only need a bee house and nesting materials, and plants with the proper leaves for the bees to use in their cocoons. You won’t need protective gear because they rarely sting, and you won’t need equipment to harvest honey because they don’t make any. You can set up your bee location in about 15 minutes. Set aside a little time to watch them when they emerge and start pollinating and getting ready to lay their eggs.

Bee activity usually stops in late August. This is when you will need to put in a little work. Collect and store the bees nesting holds with the open ends up in a dry, secure building such as a garage or shed. The building does not have to be heated. The megachile rotundata larvae will overwinter in here until spring. Collecting and storing your bees should only take an hour or so and is well worth the investment. You’ll get a healthier garden, and you will end up with more bees than you started with. Share them with family and friends to help spread the beneficial effects of leafcutter bees in your area.

Ensure Your Garden’s Pollination

Raising leafcutter bees is easy and doesn’t require much time or training. A bee house, nesting materials, and bee cocoons are quite affordable. Also, there is no need for protective gear, since they overwinter in leafy cocoons and rarely sting, nor expensive equipment to rent or buy because there is no honey to manage (only social honey bees make honey).

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.

Keys to Successfully Raise Leafcutter Bees

  1. Make sure your bee house faces east, so the bees can catch the early morning sun. The warmth will get them up and moving earlier, which will increase pollination.
  2. Make sure you have the right kind of leaves for your leafcutter bees. If they can’t find the right plants, the bees will leave your yard. This is the biggest problem people face when trying to raise leafcutters.
  3. They need leaves that are not too thick, not too thin, and not veiny. Rose leaves are a good example of what to look for. Pea plants are also recommended.

    **** Leafcutter bees build protective cocoons out of leaves #savethebees**** Click To Tweet
  4. Bring the filled nesting holes in to a dry building for the winter, after bee activity stops. This will keep them safe from pests and from harsh weather conditions.
  5. Harvest the cocoons early in the spring. You can remove pests and disease during this process, and also take inventory of your stock of cocoons.
  6. Leafcutter bees usually need to be incubated at room temperature for about 6 weeks before they develop into active adult bees. There are cocoons you can purchase that are already developed and ready to emerge, so take note of which kind you are buying.

Description of Leafcutter Bees

  1. With the scientific name megachile rotundata, alfalfa leafcutter bee females are black with pale yellow stripes on the abdomen and face. They are about two-thirds 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, megachile rotundata 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.

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