Bee-flies, tawny mining bees and blackcurrant bushes

There seemed to be dark-edged bee-flies Bombylius major all over the garden during most of April, either sunning themselves on stones or collecting nectar from lesser celandines, aubretia and primroses. 

These parasites drop their eggs near the nest holes of mining bees, where their larvae take over the unfortunate host's pollen store and complete their development at the expense of the bee's own offspring. The season for this activity in spring is quite short so the parasite and host's flight periods need to synchronise and the parasite needs to be able to find those egg-laying sites, which can be quite inconspicuous.

Bee-flies are restless, highly active insects that hover while the feed, and this makes them fairly easy to photograph, but they also spend a lot of time simply hovering in one spot, high above the ground, without feeding.

In our garden they almost always choose the area around the blackcurrant bushes to hang motionless in the air, sometimes for many minutes, and I've often wondered why they indulge in this energetically expensive behaviour, where they burn fuel in much the same way as a helicopter, simply to stay in one place. And what it is about the blackcurrant bushes that attracts them? It could be that  they congregate here to find mates, but they can easily do that at the floral feeding sites. 

I think the answer to why they congregate in the air above the blackcurrants is that one of the common pollinators of blackcurrant flowers is the tawny mining bee Andrena fulva, whose nest holes they parasitize. 

So could it be that this is where the bee-flies loiter to  identify their hosts, and then follow their pollen-laden victims back to their nest holes? If so, do they identify the mining bees visually - that orange fur does make them conspicuous - or is there something more subtle that gives away the host bees' presence - scent, maybe?

No easy way to answer that last question, but next spring I'll be watching again, to see if the hovering bee-flies do follow the mining bees when they leave the blackcurrant flowers and head for their burrows.

Bee-fly - every mining bee's worst nightmare?

I photographed this bee-fly Bombylius major on a sunny bank neat Thorsgill wood in Teesdale last week.

These furry little flies that mimic bees are parasites of mining bees and several of them seemed to have just emerged from their underground nursery in bees' nests.

Their first actions on emergence are to feed on nectar, darting from blossom to blossom with incredible speed, rarely stopping to settle and usually just hovering in front of a flower, sucking up nectar with that long and deadly-looking proboscis.Violets and primroses, both flowering at this site, are popular nectar sources. 

Few flies look so menacing but they are totally harmless - unless you happen to be a mining bee.

When mining bees dig their new tunnels and provision them with pollen for their developing larvae a bee-fly will hover close to the ground near the entrance,flicking eggs into the tunnel entrance with its tail. When the eggs hatch the larvae will eat the mining bee host's own larva.

You can find more information, a bee-fly ID guide and a video of the insect laying eggs at http://www.brc.ac.uk/soldierflies-and-allies/bee-flies

Woodland walk along the river Tees that J.M.W.Turner trod 200 years ago

This is the view of the river Tees from Abbey bridge near Egglestone, on a tranquil spring day. When the snow melts in Upper Teesdale this becomes a raging torrent, roaring through the rocky gorge. 

The woodland on the steep banks of the river here is exceptionally beautiful in spring, carpeted with wild flowers. Last week wood anemones were the star of the show; next week the bluebells will take over.

Fallen trees are left to gently decay and often develop their own 'garden' of flowers as they rot - like this one with a flora of wood anemone, ramsons and herb Robert.

Last week the bluebells had just begun to flower but it will be early May before the tree leave canopy begins to close over them. The fully-grown trees are mostly sycamore and oak.

The path winds through a dense carpet of wood anemones, high above the river.

Wood speedwell Veronica montana

When we arrived there was still a chill in the air and dew on the leaves, so the wood anemone flowers were all nodding downwards ...

..... but by mid-morning, as the sun climbed higher in the sky, they turned to face it.

This wood anemone had purple leaves.

Some early wild cherry blossom, hanging over the river.

Wood sorrel, nestling against a moss-covered tree base. The leaves fold down at night, like triangular tents.

Beyond the woodland the path passes through pastures, with ground ivy Glechoma hederacea flowering in the shelter of a dry stone wall.

Last week the first influx of warblers arrived, with this willow warbler and blackcaps singing

Last time we passed this way the elms were just coming into flower. Today their clusters of seeds were well-formed.

A bee-fly, a parasite of mining bees, sunbathing in a clearing.

Crane-flies mating.

A comma butterfly soaking up the spring sunshine after a long hibernation.

In 1816 J.M.W. Turner must have walked this footpath and perhaps sat somewhere near here to sketched this scene, at the confluence of the river Greta and the river Tees, which he painted in 1818. I like to think that perhaps he sat under this ancient oak, which would have been more youthful then, to view the scene, which you can see in his painting by clicking here.

It's a Hard Life being a Miner

Tawny mining bees often visit our garden, sometimes feeding on the gooseberry flowers in spring, but I've never managed to find evidence of their nests here. But they must nest somewhere fairly close, because we also receive regular visits from two of their parasites.

Bee-flies lay their eggs near tawny mining bee nests and their larvae crawl down into the underground nest chamber, eat their host's grub and monopolise the store of pollen that the bee lays down for it. Bee-flies are relentlessly active, which means it's almost as difficult to photograph one at rest as one in flight. But this one paused just long enough on the fence to have its photo taken, displaying its furry bee-mimic body and long straight proboscis, used for sucking nectar from deep within flowers.

And this is another enemy of the tawny mining bee, feeding on our forget-me-nots. It's a cuckoo bee (Nomada sp.) - a solitary bee that also behaves like a cuckoo, laying its eggs in bee-fly nest holes where its larva steals its host's pollen supply. Notice that it has few body hairs and no pollen combs and baskets on its legs for collecting pollen to feed its offspring; that's done by the unfortunate tawny mining bee.

This way madness lies...

Spent a hot and frustrating afternoon chasing hyperactive bee-flies around the garden, as they visited the forget-me-knots and lady’s smock flowers around the pond. Never really got the picture I was hoping for, but made an interesting discovery - take a look at the middle picture (double-click on image for a larger version). There’s a step change in the thickness of this insect’s long, straight proboscis (see top picture) and where this step-change occurs the narrow, pointed tip splits apart into a Y-shape when it withdraws from the flower. I’m guessing that when the two halves are brought back together again this reforms a narrow tube that draws up nectar by capillarity, and that this splitting-and-reforming operation prevents the formation of airlocks in the hollow proboscis. A high shutter speed reveals what the human eye can never see, even though it means that the photos have a very shallow plane of focus.