Do female solitary bees give ‘hands off’ signals to harassing males?
Female solitary bees are accosted by males especially if they believe her to be unfertilised. Fertilised females are very busy with the physical and energy demands of collecting pollen or other materials needed by them to provision or build their nests. It would be very useful for females if they could be left alone by the harassment of males!
Wasteful time or lose of nesting materials
Fleeing males can be time and energy consuming, as can repelling the males, as seen in the video. She could loose valuable pollen or nest materials, whenever a male grapples with her or she has to flee in a hurry. Grappling with males, even momentarily, could increase the wear and tear on her body and wings. Such unwarranted attention would lead them to making less foraging trips, unable to make efficient use of time for nest building and spending a longer time overall in their nest construction. It could be a huge distraction from her nest duties.
I quite often, particularly with female leafcutter bees, saw them deliberately point their pollen laden abdomens towards the sky. After a few seconds they would lower their abdomen. I often wondered why this was. What was the point of such a deliberate action? Then I realised it was probably so that they would not brush their pollen laden scopa against petals, anthers, stigmas, etc., on the flower and loose some of their precious pollen, particularly when they are nectar feeding and not pollen gathering. Loosing it would be wasteful in time and energy collecting and then having to recollect it.
Give him a sign
Without some kind of physical signal seen by distant males, it is highly likely females will be accosted by a male. How does a male know from a distance that she is already fertilised and he would be wasting both of their time and energy?
No pollen, male investigates
In the video, I noticed the female, likely blue mason bee, Osmia caerulescens, nectar feeding on yellow toadflax. She kept her tongue extended as she flew from flower to flower, saving her a little energy. The flowers are quite difficult to enter and she has to force her way between the petals. Whilst watching her, I saw that she did not have any pollen on her scopa, a sensible precaution as she would have some of it when forcing her way past the petals to reach the nectar. It was during this bout of nectar feeding a male flew into the picture, grappled with her and she had to make a quick exit from her feeding. For the male, as she was not showing any pollen, which indicates nest building and therefore already mated, she was worth investigating.
Pollen laden female display to male?
In the photograph and the video, the female, probably the leafcutter, Megachile centuncularis, whenever males were around the female deliberately displayed her pollen laden scopa by pointing it upwards, as I have often seen with other females. Then they would lower them. So besides their action or protecting their pollen from being brushed off, I suspect this is probably a deliberate action of their behalf to ward off the male harassment, “Leave me alone I am fertilised and nest building!”.
Similar behaviour from another solitary bee
It is known that female solitary bees, Macropis nuda, while foraging for nectar or pollen, outstretch their pollen laden hind legs, above their abdomens in a direct response to a males mating pounce. This effectively dislodges the male but it can then communicate to other males “Leave me alone I am fertilised and nest building!”. Why not a similar communication for leafcutter bees?
I have watched the abdomen pointing behaviour several times and not seen the males grapple with the females who displayed in this way. I have not noticed this behaviour with Red mason bees, but will look for it now! Sometimes you see things but don’t take notice of what you are actually seeing!!
Interested in Citizen Science and pollinators? The Buzz Club
For more information about solitary bees visit BWARS
For info and link to buy an excellent book Field Guide to the Bees of Great Britain and Ireland by Steven Falk
An extremely useful resource supports this book by a special web site feature within Steve Falk’s Flickr web site which furnishes extra photos and other useful resources to assist with identification.
With thanks to Jim Cane, USDA-ARS Pollinating Insect Research Unit, who prompted me to revisit some old films I made!!