Furrow Bees

furrow-bees
Furrow bees are also called Sweat bees

One of the most populous families of bees is also the most biodiverse. Furrow bees, also known as “Sweat” bees, cannot be easily characterized or quantified because their habitats are largely dependent on the region. What is common is their choice of nesting location: underground or in rotted wood. Read ahead to find out more about the similarities and differences among the various species of this burrowing bee.

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    What Are Furrow Bees?

    In North America, Furrow or Sweat bees are almost as ubiquitous as the honey bee. Although the nesting habits of this genus are largely dependent on where they are found geographically, they all burrow to make their nests.

    Why Are They Called Sweat Bees?

    They require sodium for good health, and they can’t easily find that in pollen or nectar. So they are attracted to sweat produced by humans, and their tongues have evolved into a long, slender shape to more easily “lick” the perspiration off of human skin.

    They can also maintain their sodium requirements if they are located near a beach or where flowers receive a salt-water spray.

    Which Bee Family Do Furrow Bees Belong To?

    Furrow bees belong to the Halictidae family. Bees in this family are called different names, including Sweat, Nomiine, and Shortface. The genus Halictus is specific to bee species commonly called Furrow bees, Sweat bees, and sometimes Mining bees – even though there’s another bee family officially known as Mining bees (Andrenidae).

    Where Can Furrow Bees Be Found?

    Furrow bees occur primarily in the Northern Hemisphere, with only a few species in South America, Africa, and Asia.

    Orange-legged Furrow Bee (Halictus rubicundus) is an abundant species that has extensive geographic distribution, and Ligated Furrow Bee (Halictus ligatus) is found in the northern and western portions of North America.

    In Europe, the common species is the Six-banded Furrow Bee (Halictus sexcinctus).

    Where-Can-Furrow-Bees-Be-Found
    Europe's most common species of furrow bees are the six-banded furrow bees

    What Are the Physical and Behavioural Characteristics of Furrow Bees?

    Furrow Bees are generally small bees. In California, for example, they range from 0.2-0.6 inches.

    Colour varies significantly by species, but most include some green in addition to dark brown or black. The green can also produce a metallic sheen in many species. Furrow Bees have bands of hair on the outermost edges of their abdomens, and the females carry pollen on their hind legs.

    Some of the species are solitary, but many are social or eusocial. Sometimes species practice social behaviours based on environmental factors. For example, Orange-legged Furrow Bee (Halictus rubicundus) tends to be social in warmer locations and solitary in cold, mountainous regions.

    Bees in the genus Lasioglossum are also called Sweat bees and look very similar to the Halictus genus. But Lasioglossum has bands of hair on the inner edge of each abdominal segment, while Halictus’ hairs are on the outer edge of each of those segments.

    Are There Different Types of Furrow Bees?

    The genus Halictus includes more than 330 species in 15 subgenera. In North America, there are five subgenera for ten species on the continent.

    Halictus species is so diverse that it is impossible to account for all of their differences here. However, where they do differ is in their nesting organisation and social structure. These differences will be explained further when discussing life cycle and reproductive patterns.

    Where Do Furrow Bees Nest and What Are Their Nests Made From?

    While some species of Furrow Bees bees arrange the locations of their nests differently than other species, most nest either in burrows they dug into the ground or in rotting wood. The bees that nest in wood choose rotting or partially rotted wood because it’s easier to dig than wood that has not rotted. Often, they’ll choose their nesting location based on proximity to floral or water sources.

    How Furrow Bees organize their nesting spaces is determined by whether the bees are solitary or social. Social bees live in colonies and all of the bees have specific roles to play in taking care of the colony.

    These social bees tend to live in cells that are located near each other. In some cases, the primary tunnel off the burrow is shared with multiple queens and workers. Other eusocial colonies have side chambers dug off the main tunnel by individual queens. Solitary bees of the genus live in cells that are spaced far apart from one another.

    Furrow Bee Reproduction and Life Cycle

    The life cycle of Furrow or Sweat bees differs based on whether they are solitary or social bees. Orange-legged Furrow Bee (Halictus rubicundus) is one species that demonstrates both solitary and eusocial behaviour depending on where they are located. Here is how the solitary bees differ from the eusocial bees in terms of life cycle and reproductive patterns. 

    Social populations of Orange-legged Furrow Bees are found in areas with longer growing seasons, like New York, Kansas, southern Ontario, interior regions of the Netherlands, and coastal British Columbia. 

    For these populations, females will have mated before hibernating and emerge once the weather gets warm. After emerging, they find and prepare nests and rear a brood that is mostly 75-100% female (5-8 total eggs) and designated to be workers that will help the reproducing female to rear a second brood of 10-15 offspring, of which 40% are female. 

    In this second brood, the male and females mate and then hibernate until the following year when the cycle begins again.

    Solitary populations of Orange-legged Furrow Bees occur in areas with short growing seasons like Scotland, Alaska, and the mountains of Colorado and Italy. The gynes begin to nest in late spring or early summer and rear one brood that is 40% female. The offspring mate and enter a period of dormancy (called diapause) while undergoing hibernation. The cycle begins again the following spring.

    For both solitary and eusocial species, the nests are prepared basically the same way. Offshoot channels branch out from the initial burrow tunnel and one egg will be placed in each of these tunnels along with a pollen ball upon which the larvae feed when they hatch.

    Furrow-Bee-Reproduction-and-Life-Cycle
    Orange-legged furrow bees are capable of living both solitary and social lifestyles

    What Are the Different Roles of Male and Female Furrow Bees?

    Generally, the male is there to mate, and female bees do the work of building and preparing nests and caring for the offspring. It is not clear whether the first brood of workers in eusocial nests requires the male offspring to help with brood-rearing or if they are merely sidelined until mating begins.

    Do Furrow Bees Pollinate or Produce Honey?

    Furrow bees do not make honey. Even though some species are eusocial, like honey bees, they do not need to produce honey to feed their young. A regular mixture of pollen and nectar does just fine.

    Furrow bees are known to be generalists pollinators, meaning that they’ll pollinate any available flower. The United States Department of Agriculture reported that these bees have more complex digestive systems than other bees and are able to handle the many types of pollen they take in. Some of the plants they more commonly pollinate are wildflowers, stone fruits, apples, pears, alfalfa and sunflower.

    Even though most Furrow bees are known to be generalist foragers, one recent study found that Ligated Furrow Bee (Halictus Ligatus) visited the same species of flower over and over again in a controlled nursery environment. The behaviour could be promising in commercial applications where specific crops must be consistently pollinated.

    Furrow bees are much less expensive to maintain than honey bees, so these results could be a potential gamechanger.

    Do Furrow Bees Sting?

    Furrow bees are generally not aggressive toward humans, except when they are thirsting for salt. They are also less defensive about their nesting burrows than honey bees are about their hives, and they will only sting if directly threatened. However, they may become angry if there are vibrations near the nest site or dark shadows over its entry. 

    The stings themselves – if they do occur – cause minimal pain because the stingers are so tiny. But the bee that stings will die because – like a honey bee – the stinger gets ripped from the abdomen when it catches skin, which kills the bee.

    Do-Furrow-Bees-Sting
    Much like in honey bees, furrow bees' stinger gets ripped when they sting, causing them to die

    Are Furrow Bees Aggressive Towards Other Bees?

    It is only in the eusocial nests that these bees display any kind of aggression (commonly Halictus ligatus), and it is the queen that will exhibit these aggressive tendencies. She tries to establish herself as the sole egg-producer by secreting hormones that suppress ovarian growth in the other females.

    What Is the Difference Between a Furrow Bee and a Honey Bee?

    Even though some Furrow bees are social like honey bees, honey bee hives are prepared to help the colony survive during the winter. That is why honey bees make comb and store honey for the months when they won’t be able to forage.

    Furrow bees don’t make honey and collect only enough pollen and nectar to provide nutrition to a developing brood and for their own nutrition while preparing their nests.

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