Most bees are active during the day, but there are some species that can and prefer to forage when it’s either dim or close to complete darkness. There are several reasons that make these night-time bees different from their daytime counterparts.
Do Bees Fly at Night?
Most bee species are daytime flyers. They are known as diurnal, and they restrict their foraging activity to the daytime since it’s more difficult to see and avoid obstacles when it’s dark.
But there are rare species of bees that can fly during low light and complete darkness. These nocturnal bees – mainly tropical species – have evolved to be able to see and fly at night. Conveniently, there are particular flowers (e.g. moonflower and night-blooming jasmine) that are open at night. This is an advantage for night flyers since they don’t have to compete with day-flying insects for pollen and nectar.
What Species of Bees Fly at Night?
There are at least four, and as many as seven, bee families that either fly in darkness or in low light. These families include Apidae, Andrenidae, Colletidae, and Halictidae.
From the Halictidae family, here are some of the other true nocturnal bee species:
- Megalopta atra
- Megalopta centralis
There are many more species that are crepuscular – those that fly in low light:
- Caupolicana ocellata
- Caupolicana yarrow
- Lasioglossum (Sphecodogastra) galpinsiae
- Martinapis luteicornis
- Megalopta genalis
- Peponapis genus
- Ptiloglossa arizonensis
- Ptiloglossa guinea
- Ptiloglossa jonesi
- Xenoglossa fulva
- Xylocopa tabaniformis
Species able to fly if there is adequate moonlight (at least a half-moon) are:
- Lasioglossum (Sphecodogastra) texana
- Apis dorsata
- Apis mellifera adansonii
Why Have Some Species of Bees Become Night-Flyers?
One reason why some bee species became night-time flyers is due to decreased competition from other pollinators during darker hours. You’ll notice that where nocturnal and crepuscular bees are found, there are many plants that either open only at night or produce nectar both during the day and night.
In contrast, daytime pollinators must compete for the flowers that produce only during the day. The only real competition bees have at night are moths and bats.
It’s likely that the flowers most abundant in nectar and pollen likely drove bees toward these resources even though the light was dim, which would be both early in the morning and around dusk. At these times, the flower resources are mostly untapped.
A second reason why some bees became nocturnal could be that it was the best time to avoid predators and parasites since these are both formidable threats to the bee population.
How Do Bees See in the Dark?
Bees that have not evolved to fly well at night may use image processing hacks to help them see better in very low light. They can use their brains to lengthen the period of time during which their photoreceptors collect light before they send a signal, but that could make moving objects appear blurry.
Another method is to collect the signals of all their photoreceptors in an effort to create one complete mosaic image. But this could lessen the detail in the images that are produced. Neither of these techniques works very well, and the nocturnal bees – with their larger eyes – are much better adapted to see at night.
How Do Bees’ Eyes Work?
Bees have a total of five eyes. Three of these are called simple eyes, or ocelli, and are located at the centre top of a bee’s head. The ocelli have only one lens each, just as our human eyes do. The simple eyes are capable of sensing polarized light, as well as ultraviolet and infrared light, and they help the bee with orientation.
However, only the two more complex eyes – called compound eyes – are capable of forming images and detecting patterns that help them identify particular plants. The compound eyes can see in all directions and are made up of thousands of lenses that each sense only a tiny portion or pixel of an image. All of these tiny images combined together form the complete picture image that a bee sees. The compound eyes are rather large and take up much of the bee’s face.
Are Some Bees Unable to Fly in the Dark?
Most bees fly during the day because this is the time when they can be most productive, and they use the night hours to conserve the energy they’ll need for foraging the next day. Besides not being able to see as well at night, these diurnal bees have no good reason to leave their nests at night unless they absolutely have to do so. They are able to fly in the dark but they choose not to.
However, the skill with which bees fly at night is impacted – even among nocturnal bees. The Megalopta genus (in the Halictidae family and known as the Sweat bee) includes a number of either nocturnal or crepuscular species.
A study published in the Journal of Experimental Biology (2007) found that very dim light affected the average time required for the Megalopta to land. The researchers measured the time it took to land once returning to the nest, and the slower landing times didn’t occur because the bees were flying more slowly, but due to erratic flying and error-prone, circuitous approaches.
Even with larger eyes, night-flying bees still can’t count only on their vision to guide them back to their nests. As discussed earlier, they must also use their brains. But despite using everything available to them, they are still not very well adapted to night flight.
The Eyes of Nocturnal Bees vs Daytime Bees?
Nocturnal bees have eyes that have evolved to see in darkness. Specifically, their eyes have adapted to lower light conditions by becoming larger over time than diurnal species. For example, one study discovered that the Megalopta sweat bee (a nocturnal species) had larger compound eyes, larger facets, and an optical sensor that is 27 times greater than Apis mellifera (the European honeybee).
However, it is the ocelli that are significantly larger – in proportion to body size – in nocturnal bees compared to diurnal bees. An interesting comparison shows the ocelli of the diurnal Carpenter bee (Xylocopa ruficornis) measuring less than half the size of the nocturnal Indian Carpenter Bee (Xylocopa tranquebarica)
Not all night-flying bees can see in pure darkness. Some require a low level of light, either twilight or moonlight – and are known as crepuscular bees. They are active during both dawn and dusk.
Is Geographical Location Correlated With Night Flight?
Some species of night-flying bees live in very dry areas or at higher latitudes. They may have adapted to night-flying because it’s more preferable to forage when the sun isn’t so hot and water isn’t as readily available.
But most of the nocturnal and crepuscular species live in tropical or subtropical regions. Many of the plants in these areas are very fragrant at night and produce a lot of nectar. Nocturnal and crepuscular bees may have adapted to nighttime flying because this was a way to avoid competition from the many more diurnal bees and other pollinating insects.
Do Nocturnal Bees Forage Like Diurnal Bees?
It’s admittedly difficult to observe the foraging habits of nocturnal bees because of the lack of light, but there do seem to be similar strategies among both diurnal and nocturnal bees.
Both diurnal and nocturnal bees will visit flowers that may be far away from their nests. This is of course easier for diurnal bees because they can see better to find their way home.
The diurnal bees will rely on their eyesight, and identify landmarks on the foraging path so they can both return to their nests and also remember these locations for later. Honeybees pass this information onto other bees in the hive.
Nocturnal bees can also learn where their nests are in relation to floral landmarks – and they do use their polarized vision in this effort. But their flight pattern is somewhat different from diurnal bees.
As they fly away from the nest, they’ll turn in mid-air to face the nest – perhaps to take a mental picture of this landmark. Then they’ll fly in large arcs so they can survey all of the potential landmarks. It’s not known whether they are learning where the landmarks are on their foraging path when they fly in this way.
Does Artificial Light Impact Night-Time Pollinators?
A 2017 study reported in the journal Nature found that artificial lighting was drawing nighttime pollinators away from floral resources and that over the last few years, light emissions have increased by over 70 per cent in North America and Europe.
The study’s lead author found that light exposure (streetlights, for example) reduced pollinator visits by 62 per cent. The artificial lighting also drew 29 per cent fewer species, compared to dark fields that are visited by nearly 300 species of insects.
The researchers urged communities and citizens to restrict artificial lighting where possible and encouraged planting more night-blooming plants.
Nocturnal Bees Are Rare Because Bee Biology Hasn’t Made Night-Flying Very Efficient
Even though nocturnal and crepuscular bees show evolutionary adaptations to their eyes, these adaptations have not allowed nighttime bees to navigate as well as daytime bees. The night-flyers will continue to forage during darker hours to lessen competition and enhance their safety.
It will be fascinating to see if evolution will bless these bees with even better vision as they increase the pollination of plants that depend on these kinds of bees. We should play a role in this grand experiment by continuing to plant the floral resources that are particularly dependent on the activity of nocturnal bees.