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Sunny honey

Temperature drop at sundown is one reason bees get stranded. Their flight muscles must be warm enough to work. Another reason is that foraging and homing are predominantly visual tasks, and bees that are active during the day do not see well in dim light.

Day-active insects typically have apposition compound eyes, in which light reaches the photoreceptors—light-detecting cells in the retina—exclusively from the lens located directly above it. In contrast, nocturnal insects, including most moths, typically have superposition compound eyes, in which each photoreceptor receives light from hundreds, sometimes even thousands, of lenses.

The light-gathering power of superposition eyes gives them a sensitivity advantage compared to apposition eyes. Surprisingly, although all bees have apposition eyes, several bee species forage at night or during twilight. One species, the giant Indian carpenter bee, has even been observed foraging on moonless nights.

Bee species that fly between sunset and sunrise generally live in warm desert areas or in forests in tropical or subtropical regions where the flowers of many plants open only at night. Competition for nectar and predation are often reduced during nocturnal foraging.

To overcome the disadvantage of apposition eyes, bees that forage in dim light have various visual adaptations. Some lie within the eye itself; others are located in the neural circuitry that processes visual information. For example, the three simple eyes, or ocelli, that bees have on the top of their heads between their compound eyes are considerably larger in these species. Ocelli are thought to be involved in flight control.

Each lens within the individual eye units that constitute the compound eyes of night-flying bees is larger relative to body size, and night-flying bees typically have more of these eye units. Their photoreceptors are more light sensitive. Not only are the signals from the photoreceptors sent along the usual visual channels to the brain, but these bees also have specialized nerve cells that sum the outputs of neighboring visual channels.

Regarding the mortality you witness among bees that fail to take cover when the light dims and the temperature drops, some bees die from age and injury. Because of the way bee colonies divide tasks, foragers are the hive's oldest workers, and bees don't get to retire.

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