Buzzzzzzz!!!!!

There was definitely a buzz in the garden today. The usual Anthophora plumipes males were now joined by the first female of the year (above), feeding on the Pulmonaria. The Pulmonaria, unfortunately, was in the shade, so I couldn't take as sharp photos as I would have liked. A male Osmia bicornis (previously rufa) was patrolling the grape Hyacinths and a female Andrena fulva made a brief appearance. Just on cue, as the Cherry, a favourite of this bee, started to bloom yesterday.
 A Green Shieldbug was out sunbathing, also the first of the year. Many young wolf spiders were out too in the sun, stalked by my young cat, who likes to hunt and eat them, to my dismay. A Peacock butterfly passed by, but didn't settle.

Unidentified Andrena sp. on a dandelion.

Male Osmia bicornis

Male Anthophora plumipes.

Green shieldbug

Flea beetle, Altica sp.

Solitary bees are back!

In the last week I have been spotting more and more species of solitary bees around. First on scene, as usual, at the beginning of March, Anthophora plumipes, the Hairy Footed Flower bee. Then, a couple of days ago I saw the first Andrena fulva (Tawny mining bee) and yesterday I saw a couple of unidentified Andrena sp. (below). Today the garden was buzzing with at least 4 males A. plumipes, and a female feeding on Erysimum, and the cast was complete when in the afternoon a male Osmia rufa (Red Mining Bee) turned up and stopped to bask on the wooden frame of the conservatory (above). All of them have broken records as to how early they have appeared in the year compared to my previous records, which is not surprising given how mild this winter has been. From a few days to a few weeks before previous years, just as many flowers are also blooming early. The Red Mason Bees breed in our bee hotel, but we have been making another one from reclaimed floorboards and canes, I will push to finish it this weekend as females won't take long to appear.
 Are your bees early too?

Andrena sp.

Another Andrena enjoying a Dandelion

The new bee hotel in construction

Tawny mining bee nesting aggregations

I have been posting on the Tawny Mining Bees, Andrena fulva, recently. I have been watching suitable nesting sites for signs of activity and today I came across many nests located in groups in several grassy areas. It was a bit windy and the female bees often missed their nests when landing. Instead of walking the short distance, they would fly again, carry out what looked like a positioning flight, and landed on top of their nest mound and got inside.

 Some females seemed to be looking for good places to nest, and tentatively would start digging in the soil amongst other nests.

Males were patrolling around, jumping on passing females. Tawny Mining Bees, like many other bees and wasps, tend to nest in clusters, many nests will be located near each other, when apparently suitable habitat is plentiful around them. They like areas of short grass and the fresh pellets of soil soon stick out like mini mole hills on lawns, verges and park greens.
 Why do bees nest in this way? They are solitary, so each bee will make her own cells and storage pollen and nectar toward her eggs. Apparently bees are able to detect the smell of conspecific active nests and preferable fly towards them; they also tend to return to their natal sites, and, obviously, successful nesting areas would tend to increase their nest density with time. These are proximate explanations, they tell us how bees actually find the nesting sites. But do bees actually benefit from nesting in an aggregation as opposed to doing it on their own? Aggregated nests must have a strong benefit to counteract the costs associated to the behaviour, such as increased competition or higher diseased transmission. Five hypothesis as to the adaptive value of nesting aggregations have been put forward:
1) Bees might be selecting very specific environmental conditions to locate their nests, for example, soil of a particular consistency or nectar sources nearby. This hypothesis has been investigated and appears to hold for some species, but not for others.
2) Nest sites might act as "information centres", where bees would find from others where the best foraging resources where. This, although possible, has no empirical support.
3) Newly nesting individuals might nest in aggregations because they act as markers of successful nesting sites.
4) Bees might benefit from reusing old nests, so that some of the costs of digging would be offset.
5) Nesting communally might offer some antipredator or antiparasite benefits, maybe by confusing predators, or communal defence. Data in support of this hypothesis is conflicting: parasites can either favour aggregations, by being more effective the less aggregated bees are, or dispersed nesting, when they locate clumped nests more effectively. Some bees gain protection from parasites by nesting communally, for example, as I covered in the recent post on Melecta, individuals of the host species Anthophora attack parasites near their nest, therefore conferring some protection to neighbouring nests.
Whatever the reasons, Andrena fulva nesting aggregations must be one of the easiest to observe in British solitary bees. Just look for their little molehills on the grass. A little red head might be peeking from inside.

References
Michener, Charles D. (1974). The social behavior of the bees: a comparative study. Harvard University Press. Other: ISBN-13: 978-0674811751

Rosenheim, Jay A. (1990). Density dependent parasitism and evolution of aggregated nesting in the solitary Hymenoptera Annals of the Entomological Society of America, 83 (3), 277-286

Melecta, a cleptoparasitic bee

The plum tree started flowering last week and today it was buzzing with bees. I counted six species, Bombus terrestris and lapidarius queens, Anthophora plumipes males and females, Andrena fulva, with males actively patrolling the branches, and the first males Osmia rufa of the year. Later, a black bee with white and grey hair patches and dark wings turned up. It was Melecta albifrons, a cleptoparasite of A. plumipes. I haven't found much information on M. albifrons so the following life history account mainly comes from a study on the American species, Melecta separata. Melecta females parasitise Anthophora species that nest communally. They explore their host's nesting aggregations in search of finished nests. A female, upon finding a nest will start digging and breaking open the sealed entrance. Then she will lay an egg on the roof of the cell, seal the cell and replug the nest. Anthophora females usually attack the cuckoo bee, but she either flies away or if inside the nest it defends herself with her sting. The Melecta larva hatches a day earlier than the Anthophora's and is very mobile. They pierce and drain the Anthophora egg and any other Melecta eggs that she finds in the cell with their long sickle-shaped mandibles. Only one Melecta larvae survives, as if two are born at the same time one will kill the other. The larvae then feeds on the syrupy mixture of pollen and nectar intended for the Anthophora larvae. Subsequent larval stages lack the long mandibles of the first stage. The following year a Melecta will emerge from the cell, having consumed the food intended for Anthophora grubs. In a M. separata nesting aggregation 20% of the nests were parasitized.
The Melecta albifrons visiting my plum showed a very different behaviour from other bees, sluggish, like she didn't want to fly too much, climbing over the flowers to reach each of them and feeding showing a very long tongue. The bee stayed for quite a while feeding on the plum flowers. M. albifrons has a very similar distribution to its host in Britain (click here for distribution map), reaching up to the Yorkshire Wolds in the north. Its peak flight period is a few weeks after the emergence of the host, and flies from April to early June. Given that it doesn't need to collect pollen for provisioning its brood, the bee is not fussy about what flowers to visit, and tends to fly at short daily periods - the warmest - as they are less endothermic than their Anthophora hosts, as shown in the figure below.

References
Thorp, R. (1969). Ecology and Behavior of Melecta separata callura (Hymenoptera: Anthophoridae). American Midland Naturalist, 82 (2) DOI: 10.2307/2423782
P. G. Willmer and G. N. Stone (2004). Behavioral, Ecological, and Physiological Determinants of the Activity Patterns of Bees. Advances in the Study of Behavior, 34 , 347-466 : doi:10.1016/S0065-3454(04)34009-X

Making cherries

We've got a small cherry tree in our garden. In addition to making a spectacular show when it blooms, it produces the sweetest cherries and, although the crop can be a bit hit and miss depending on the spring weather, it is a bug magnet for a few months. The tree only started flowering a week ago but today was buzzing with bees. I spent some time this morning watching the blossom and trying to ID the bees that are feeding on it or visiting. Anthophora plumipes and Osmia rufa males have incorporated the tree into their patrolling routine, circling around the blooms, chasing other bees and keeping track of the females. Beautiful, velvety shiny red female Andrena fulva were also feeding on it as were female A. plumipes. I stopped counting the honeybees as there were quite a few. To the high pitched buzz of the Anthophora bees, the deep buzz of queen Bombus lapidarius and Bombus terrestris was added. These busy lot of creatures were involved, without realising it, in fertilising the blossom and contribute to making the cherries that hopefully we'll eat this summer.

Peacock butterfly

Bombus lapidarius

A full Andrena fulva sunbathing near the tree.

Outside the blooming season, which lasts a few weeks from April to May, the tree growing buds are covered on black aphids that in june produce a sweet sap, loved by bumblebees, especially Bombus terrestris and Bombus hypnorum. I have also seen Bombus pratorum feeding on the nectaries at the end of the leave stalks. Aphids also attract scores of ladybirds. The cherries themselves are prized by wasps - and birds.