Ladies first!

Here I will explore the Wool carder (Anthidium manicatum) (Megachilidae: Anthidiin) females’ behaviour, nesting etc. and then go on to the males. Unusually for solitary bees, female wool carder bees, are smaller than males and females generally emerge first in this species. Also unlike many other species, the males die first, leaving the females to make their nests and forage for the provision of their offspring. Whereas male and female wool carder bees fly around for about the same period of time together. They are generalist feeders and after their natal flight, they will forage for food and seek out suitable nest sites usually inside pre-existing cavities. They sleep overnight in such cavities waiting for the males to emerge. Obviously, during the pre-mating days, the females will need to forage for food and this would give them a great opportunity to seek out the optimal plants for all their needs, in peace, before the males arrive.

Interestingly, they started their nest as you can see in the film, presumably in preparation for the male emergence and mating, when the nest building would be in earnest. I never saw any males when filming for the first few days, just the females foraging and resting inside nest boxes with the evidence of nest-building materials inside a cavity they were each using to rest. I do think that although I had a few yarrow plants, there simply were not enough plant hairs on them to sustain further nest building as per the film and the females abandoned the partially constructed nests to nest elsewhere, probably where a better supply of nesting materials was located.

Lamb’s ear, an excellent wool carder nest material provider

Nest sites

They are rather an opportunistic nester, using pre-existing cavities in walls, hollow plant stems, larger beetle exit holes in deadwood, window frames and even metal chair arms! I do feel the females start their nest before they mate with the males. It could be a few days later that males appear so why waste the time doing nothing else than feed? Plus various man-made objects In many of the papers I have read, researchers state that they are scattered far and wide in the wild and therefore hard to find. So I’m proud to say this includes my Nurturing Nature nest boxes!

Females collect plant secretions

Many of you will be aware that solitary cavity-nesting bees use various plant materials to make their nest, from plant leaves, masticated plant materials, resins, and plant hairs, a kind of wool-like material covering leaves or stalk/stems of certain plants. Some solitary bees also use plant resins, which are well known for their water-repellency, antimicrobial and insect-repellent properties and are likely to protect young bees inside their cells as well as the forage. Although we only have one species of wool carder bee, they do not use resins, whereas Falk states that few American species do.  Muller (1996) discovered that female wool carder bees also make use of ‘extrafloral trichome secretions’. They collect the secretions using a specialised tarsal brush on each of their legs, by brushing against the secretions whereby they are absorbed probably by capillary action onto the hairs, using plants from the Pelargonium family. You may better know some of them in particular as geraniums, which have seeded heads that resemble a stork’s beak. The females only collected the secretions during individual nest cell building which they deposited onto the wool. No deposits were made when a cell was used to deposit forage. This would make sense as the forage could be contaminated with what is an oily secretion that has beneficial properties for the health of the bees during their time in the cell. Eating it would not be a good idea! Observers saw the bees forage for just these secretions which can be seen as brownish droplets, deposited on the outside of the nest below. There may well have been other droplets deposited throughout the wool, used to glue the wool threads together, or dare I say knit the wool strands together! She may also, like the common yellow face bee, possibly apply additional substances originating from her Dufour gland. They hypothesized that the secretions may serve to waterproof the cell, prevent microbes from attacking the pollen/nectar forage, protect the larvae and/or deter nest robbing. So it appears this bee provides its offspring with some type of protection from attack

Plant secretions are deposited onto the wool by female wool carder bees (A. Muller 1996)

Disguises the bee odours

Almost 20 years later Eltz et al (2014) using more modern techniques and equipment found that olfactometer tests suggested that trichome secretions reduce the attractiveness of the odour of the host brood cell to parasitic wasps.

Titbit of info! Did you know that these bees have been called the most widely distributed unmanaged bee in the world, because of their expansive native and non-native range (Strange et al 2011)

Mating strategies

Whereas most species of solitary bee females emerge first. Males have to be quick to find and mate with virgin females numbers of which are declining, as they mate just once. A very limited resource. This is known as selection pressure. Therefore females will resist attempts to mate again. Not so with wool carder bees. Let’s have an in-depth look at their different strategies. 

Female solitary bees usually only mate once, but females and males of this species mated many times. Females mate not just once but continuously over their reproductive lifetime, Svveringhaus et al state that besides being polyandrous, females have mated with intervals as short as 35 seconds between copulation. Males are polygamous. Depending upon their size and the size of other males in the area, may defend territory where nectar, pollen or nesting materials can be found. It boils down to a strategy known as “Late male sperm precedence”. In other words, the male who mated the last was more likely to father any offspring. There is an excellent article that explains this in more detail by Africa Gomez at her brilliant website  ‘Why do male Wool-carder bees defend a flower patch?’ species.

In terms of male size, size matters. The spoils go to the victorious gladiatorial male wool carder bee. He will be the fittest, strongest and largest specimen. You can see a typical example of a fine specimen in my film,  ” The Frantic Antics of the Male Wool Carder Bee”, some of which is incorporated into this film. It reminded me of the film “Highlander” whereby male warriors sought out and killed other male warriors as “There can be only one”.

Abdominal mace!

A lethal weapon of offence carried by the male Wool carder bee

To back up his mating territorial claim, males are armed with 5 sharp ‘mace-like spines’, at the end of their abdomen. If another male or other flying insects arrive or feed in this area he will attack.  Wirtz et al describe how he will ram into the intruder at high speed, and shortly before the moment of impact, he curves his abdomen forward to hit with the long spines. I have watched this many times when an intruder is feeding on a flower. He will hover at the rear of the intruder, then ram it and grab the intruder whilst they are still feeding, in a bear-like ‘hug’ and press the mace-like spines into its body. Shortly before impacting the intruder, males curve their abdomen forward to strike at the intruder with their 5 spined mace-like abdominal tips. The intruder can be injured, such as broken or punctured wings, maimed, wounded or even killed. The bumblebee male was attacked several times by the same male wool carder bee and was unable to fly. Crawling up to the top of plants, buzzing its wings but falling to the lower vegetation or ground several times. He was now probably doomed to die. Wirtz et al describe that upon closer inspection flying insects that were attacked were examined and found to have punctures in their wings corresponding in size to the deadly spines.

Obviously, every wool carder male cannot be a combative and strong gladiator! Most will probably fail that test and not be able to defend a territory from other males. Even if they did manage to carve a small ‘productive’ territory for themselves territorial disputes would inevitably lead to them being evicted by a larger male. What happens in real life then? I was fortunate enough to actually observe in my garden. Once the dominant male ‘takes’ over one territory, he starts to make exploratory forays into other males’ territory or other areas, which may offer rich pickings. This could well be to expand his ‘real estate’ to gain access to more females, more flowers are flowering which will attract females or because his previous real estate is fading as regards flowers that will attract females for their own nesting material usage. My male expanded into the immediate adjoining area incorporating it into his ‘ownership’ portfolio and continued hovering, patrolling, foraging, chasing, mauling and mating. He had enough suitable flowers in his area for the time being. He did not enter the wildflower meadow for some time. But the smaller males did. A safe zone. For now.

A temporary safe zone

Over time the smaller males left these patrolled areas and moved to the safety of the much larger and more densely flowered wildlife meadow. This contained many taller flowers, and grasses providing cover for these males making it much more to difficult fly between and difficult for the gladiator bee to focus on an individual to be attacked. He did spend a lot of time hovering and closely inspecting other insects, deciding either to mate or maul, especially when an insect is feeding on a flower. I expect it may be easier to maul an insect when it is stationary on a plant or resting on something than attack it when it is moving. The denser vegetation and larger leaves than the ‘gladiators’ real estate’ offered many more escape routes for the smaller bees. And also allowed copulation with females that did enter to forage. It was funny really as I observed this attempt of a takeover by the gladiator into the relatively ‘safe zone’ of the larger meadow. He had to spend more and more time patrolling this new area, which was much larger and denser, during which time the smaller males flew across the ‘border’ into his estate and mated! They had learnt their lesson and bided their time. If only he knew!

Mini estates

Another strategy used by smaller non-territory males is to attempt to forage and mate in other males’ territories whilst that males themselves are ‘otherwise occupied’. A subtle explanation as used by Severinghaus et al. They go on to state that females do not reject smaller nonowner males at a higher rate than larger owner males; their choice for male size appears to be indirect, based instead on food resources. Hence there were several females entering the ‘safe zone’ a few feet from the gladiator’s estate probably because the nectar/pollen was just ripe for the talking and their usual supply in the estate may have been diminishing or just starting to become less easily available.

Nest materials

Falk states they use furry leaf surfaces, including great mullein, woundworts, yarrow and lamb’s ear. See the film “Flowers to Attract Wool Carder Bees” Other plants are also used to make their nests. So females have to choose plants for nesting materials AND plants that can supply themselves with food and forage for their offspring. Lamb’s ear can provide both.

Plant hairs-aka wool

They use their sharply toothed mandibles to remove wool-like hairs from suitable plant stems and leaves, moving downwards as they gather up this material and roll it into a ball. This must be easier and much quicker than pushing the wool ball upwards as they cut the hairs moving upwards. This takes about  Roll them up into a ball under their thorax which, Benson describes as a cage, and carrying them to the nest site where they tease them open to make their nests. Then like other solitary bees forage for pollen and nectar lay a single egg, seal the cavity and start again.

Choose the right lamb’s ear

Lamb’s ear, Stachys byzantina is a top woolly plant for them with soft spikes of woolly, pink-purple flowers appearing from June to September.  I made the error of not planting a flowering species, Stachys byzantine “silver carpet” It just spread and spread but as a carpet has never flowered! Looking at the way they collect the hairs, having flowers to attract them lends itself more quickly for them to harvest the hairs along the underside of the leaves and carry on straight down the stalk.

However, recent research by Kelsey et al (2017)  has shown that when the females shave the wool from the lamb’s ear, the plant gives off a certain Volatile Organic Compound (VOC) which then can attract other females to that particular plant thereby causing it damage. If you have the time do read it.

Almost 20 years later Eltz et al (2014) using more modern techniques and equipment found that olfactometer tests suggested that trichome secretions reduce the attractiveness of the odour of the host brood cell to parasitic wasps.