The trials and tribulations of Rusty, a male Red mason bee looking for a mate (1)

Rusty, a male Red mason bee (Osmia bicornis) has a fast and furious life looking for a suitable mate in his short life. Competition is fierce. In the wild, the females can be very widely dispersed, males fly around looking for suitable nest sites to find scare females. Rusty will mate and move on to find another, (scramble competition polygyny). Therefore a territory to defend would not be advantageous to him. He simply feeds himself and tries to mate with as many females as possible. He will encounter other males, mistakenly mount another male, grab other males, often when one is stationary on a flower or just waiting near a possible nest site and pounce on them just as they are about to fly away, with both males crashing to the ground. In my case concrete slabs under my nest boxes! That must hurt! They will investigate other flying insects, even crash into them, including the similarly coloured queen Bombus pascuorum as shown on the video! Why do they do this?

Good morning Rusty!

Searching for a mate – Leaving the nest site

Rusty will use nest site cavities with other males to rest during the day or inclement weather and sleep overnight inside empty cavities in my orchard nest box/solitary bee boxes. When they leave to forage depends on the temperature, how windy it is, rain, hail, fog, etc. Not forgetting the wind chill factor! If it is a dry, sunny and windless day they may leave to feed around 12C. Even at 12C, sunny and dry, if there is a chilly wind or a windy dull day, they will sit it out. If its not around 12C or above they tend to sit it out. They leave much earlier in the day than the females, who like it sunny and warm before they leave, especially if they have not yet started to build cells. Rusty often returned to his natal nest site, the orchard nest box, and visits various solitary bee nest boxes I have in the garden. He will adopt several strategies to seek a mate.

Male mate seeking strategies

Visitations to nest boxes and other sites by males

Often males visually checkout the empty nest cavities by either entering one completely; visiting one by simply landing and looking inside then fly away; flying visits to several cavities checking each cavity one by one, briefly landing outside the cavity for a quick ‘look see’ doing the same thing with at the emergence holes of my nest boxes; visiting nest boxes with a quick fly over then fly away; half entering the emergence holes or cavities; landing a short distance from the cavity entrances or emergence holes and waiting to pounce; landing and waiting right outside emergence holes and cavity entrances; entering an emergence hole going into the emergence chamber and checking on the cocoons inside; waiting inside the emergence chamber; actively visiting cocoons that still have bees inside and even mounting empty female cocoon cases. I have seen males frantically trying to mount females as they were still inside the cocoon chewing their way out and were almost out. Many succeeded in mounting! Flowers are visited as are sun basking areas used by other Red masons on the lookout for a mate.

Rusty on male Red mason bee

Fuel ‘n’ go

I have actually seen individual males check out several cavities, fly to the nearest fuel providing nectar flowers a few feet away, feed on a few and then fly straight back to join the other hopeful males! Don’t want to miss their chance! I suppose this makes sense. Why go wandering off searching the area for a new potential nest site or a female, when they know where a nest site is, they emerged from it and females are present either still inside their cocoons, emerging or nesting? I have also seen males fuel up for longer, investigate nearby and then fly away to a neighbours garden, especially when there are many males flying around the various nest boxes. I expect they soon return though! I have more bees and flowers!

Pounce and mount a male

Whenever the males pounce it is generally much easier to mount the other bee when it is stationary and has landed, whether on a flower at a rest site , inspecting a cavity, even pounce whilst a male has mounted a female! The ‘pouncer’ male approaches by flying towards its ‘target’ (it could be another male, a female, both or another insect!) from behind and grabs it with its legs landing on top, then mounts it. The pouncer male has always been flying prior to pouncing. Even when there are no females around the males perform pouncing and mounting on each other. Only in the confines of the emergence chamber have I seen males pounce on females from the front, whilst they were still chewing their way out! They could not fly away and had no choice!  A riskier tactic happens in flight, one will try to pounce and mount the target, crashing into it and they both tumble to the ground or break off before hitting it.

Why pounce and mount another male?

With so many competing males, Rusty may only get one chance. It makes sense to take a chance. The flying insect nearby may just be a  female, better to try than miss out on a potential mate. It certainly takes its toll on the males. They are born vibrant red, full of red hairs on their abdomen and with a few on their thorax. As time progresses, the wrestling, jostling, pouncing and mounting, grabbing, bumping, tumbling, crashing, colliding in mid air and to the ground starts to tire and wear them out. Their hairs fall out revealing a shiny bronze-like abdomen, their wings become battered and worn. With such a competitive, combatant and stressful life style, no wonder they do not live very long!

Why chase other insects?

Why waste time, energy and effort on chasing other insects? Time that would have been better put to use searching for a suitable female to mate? When competition is so intense, with many males pursuing a diminishing number of virgin females, better to check out that one possible chance and make a mistake than miss out completely by a second or two. Hence insects that resemble a female are investigated. If females far outnumbered the males, or the females mated more than once, no doubt Red mason males would have evolved a different strategy.

Watch Rusty, from egg, larva, cocoon, chewing his way out, emerging as a handsome male, trying his luck, pouncing and mounting, patrolling an area, investigating ‘likely’ females and methodically investigating nest sites. Its all go! Is he successful? Mounting does n’t always mean mating!

Part 2 coming soon!

Find out more about Red mason bees from BWARS

Download BWARS Red mason info sheet here