It’s true, nocturnal bees exist. Bees are generally considered a day-active creature, but there are many species around the world that have evolved to love the night…perhaps because their favourite flowers open at night, or maybe they just prefer to feed in peace and quiet!
Because bee species, like most insects, are very sensitive to cold temperatures, most of these nocturnal bee species are found in tropical and sub-tropical areas. One species is known from Australia and it’s found in north and central Queensland. It’s likely that others exist, but they either haven’t been found or night activity hasn’t been observed yet.
I have lived in Albury, southern New South Wales for the last few years. The region’s climate is classified as temperate, with warm/hot summers and cold winters. The town is about 165 m above sea level, but only about 1.5 hours drive to the snowfields. Suffice to say, I didn’t think it would be the ideal spot to find a nocturnal bee.
In February 2016, I noticed something unusual in the solar party lights hanging on our front balcony. Tiny bee corpses started appearing inside the plastic light globes. I would collect them and find more the next day.
They were all the same species – thanks to Bernhard Jacobi for identifying them as Hylaeus euxanthus. Bernhard suggested that a female may have built nests in the light fittings and these were the emerging adults that couldn’t find a way out. However, I pulled the lights apart and couldn’t find any traces of nest material, so I wonder if there is more to the story.
This summer, I found more of the same species as well as two individuals of another species (looks like a Lasioglossum. UPDATE: just checked these two individuals under microscope and they are small Crabronidae wasps, not bees). It seems that these bees are attracted to the party lights, but why mostly just this one Hylaeus species?
Is it a night-active species that hasn’t been noticed before? And in a temperate region? The long twilights we have here in summer may mean nocturnally-inclined bees can be active for longer, and warm nights are often in the range of 17-25 °C (optimal daytime foraging temperature for most bees).
Are my party lights working as a light trap? The lights have a very sensitive solar panel, so the lights don’t come on until well past sunset. They are also quite dim…optimal mood lighting for a party, but not anywhere near daylight. Kelber et al. successfully trapped tropical nocturnal bees in Panama rainforest on a white-sheet light trap (a standard method for observing night-flying insects like moths). But they used a UV black light, which is not quite the same as my party lights.
Are floral scent cues interacting with the party lights to confuse the bees? Recent work suggests that floral scents play a role in guiding nocturnal bees to their food source. My party lights are hanging on the front balcony, surrounded by steel, slate and cement. The nearest plant in flower at the time I found these bees was a lantana bush, a butterfly-pollinated plant that is only occasionally visited by native bees (and I’ve only ever seen Amegilla and Lasioglossum species visiting the lantana flowers, never a Hylaeus). The street trees (Corymbia sp.) and a teatree (Leptospermum sp.) in our garden were the closest other main flowering plants at the time, both around 4-5 metres away.
Last week, I found more dead bees and opened the light globe (during the day) to collect them. I found three live adults walking around inside the plastic cap looking a bit lost, so I released them. Are the lights perhaps roosting spots? And are the bees attracted to them because of the light, or because of the warmth?
© Manu Saunders 2017
Ecology is not a dirty word 
Interesting. A farmer whose blog I read found that her chickens were still attracted to light bulbs in her shed when she switched to non-warm energy efficient bulbs, so they were more interested in the light than the heat. But of course chickens are different to bees!
Could the lights be turned off if they’re killing the bees?
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I suspect it is more likely the light attracting the bees too! 🙂 Yes our lights can be turned off. The bees only appeared in them for a couple of weeks of the year, so we left them up for the rest of the year.
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Didn’t know there were night-time bees, that’s very interesting. It might be a bit cold here during winter in the Yarra Valley for any of them to live in my garden, but now I might look out for other unexpected visitors in the dark. Thanks!
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