Sunday, 3 January 2016

Ivy Bees

No need for a long walk for this posting as the events unfurled no further than a couple of yards from my front door. This entry has been updated for the first year 2010 and each subsequent year. Over the last, at least four years my garden has been taken over briefly by a 'foreign invader', a species that has gradually moved in from the continent. Here is what I am talking about:

Ivy bee,Colletes hederae

Its yellow bands might make you think 'wasp' or possibly hoverfly. In fact with help from local experts they have been identified as 'ivy bee' (Colletes hederae). Quite appropriate as it is on ivy flowers. Here is a view of one from the top, hovering over my front lawn.

Ivy bee

I first noticed then on 11th September 2010. There was a mini-swarm of them darting around the edge of the lawn. From a distance they looked more like flies because they were circling around. Looking down, however they were indeed forming a ball of writhing bodies. Here are a couple of shots of what I saw.

Ivy bee,Colletes hederae,ball
Ivy bee,Colletes hederae,ball

So this made me think of swarming of honey bees, when young queens leave a hive to form new colonies. But these were only a dozen or so individuals and not hundreds. Like many people for a long time I associated bees with honey and that is about that. I knew about bumble bees too, but the thought that they seemed a little too big and furry to fit conveniently in hives did not trouble me too much. I learnt that these new garden visitors are solitary bees like bumble bees, gathering pollen to build a burrow for their offspring underground. For the ivy bees the underground nature soon became apparent when holes started to appear in flower beds and dotted over the lawn.

Ivy bee,Colletes hederae,burrow

After more study, and a little trepidation of getting close, entirely unprotected from potential stings (in fact they are very loathe to sting, and are disinterested with anything going on around them), I did catch them in the act of burrowing; here is one ivy bee going down.

Ivy bee,Colletes hederae,burrow

And an ivy bee just coming up

Ivy bee,Colletes hederae,burrow

to finally fully emerge

Ivy bee,Colletes hederae,burrow

So what are they doing down there? The chief clue comes from this strange sculpture. I believe it is the discarded pupal case of a bee. Every autumn, just as the ivy comes into flower (typically September) the bees emerge from these cases, mate and then dig burrows ready to lay eggs of the next year's brood. I am grateful to local experts for helping identify them. You can find out a lot more from the BWARS web site (that's Bees Wasps and Ants Recording Society), this turned out to be the first time they have been recorded as far north as Berkshire.

Ivy bee,pupa

They are harvesting pollen from ivy. This late in the year ivy is pollinated chiefly by the few wasps and flies that remain, so the 'invasion' of ivy bees is not going to have a bad impact on 'native' pollinators.

Ivy bee,ivy,Colletes hederae

The pollen is deposited down the burrows for the larvae to feed on. I have found it hard to catch them clearly carrying the pollen down the holes; this is the best I have managed.

Ivy bee,Colletes hederae

They sustain themselves on nectar from anything that happens to be flowering this late in the year. In my garden this includes Sedum spectabile.

Ivy bee,Sedum spectabile

And also Abelia grandiflora

Ivy bee,Abelia grandiflora

If you want to learn all about these delightful little creatures please listen to the November 2013 Living World programme on BBC Radio 4

2011 Update

Last year all activity ended on the night of the first sharp frost (11th October), so they had only been active for about a month after emerging. In 2011 I waited with anticipation for them. So I was delighted when I spotted the ivy bees up to their 'swarming' tricks again on 3rd September 2011.

Ivy bee,Colletes hederae

The weather this autumn has been mixed. First it was wet, windy and cool, which they can not have appreciated, and then at the end of September record breaking heat. I watched them a little more carefully, and noted that they can take several attempts to locate the burrow, they land, wander around a bit 'looking' for the burrow and then usually fly to the correct location. Activity tailed off towards the end of October (last one seen 19th October 2011) with only one or two rather bedraggled individuals left. Some of the hairs seems to have worn away on one side.

Ivy bee,Colletes hederae

They have done well though, judging by the number and area covered by burrows. Last year activity was in a narrow band of south-facing sheltered lawn, which must have given them most warmth; an area of about two square yards (or metres). This year the ivy bees have spread to more shady areas, about six square yards, so may be it is dry soil that they need, it has been notably dry the last few weeks. It is difficult to give numbers, as one female can make multiple burrows, and at any one time many are out foraging, some underground, so I'd guess there were a couple of hundred individuals in all. I wanted to say ‘colony’ but apparently that is incorrect, as they do not ‘live together’ just close to one another so I should say an ‘aggregation’ of ivy bees. Also reading around I find that the eggs probably laid last contain the males, nearest the ground level so that they emerge first, once the males have mated they do not take any further part in bringing up the brood, I presume they just wander around on the lookout for more females.

Ivy bee,Colletes hederae

2012 Update

With a very cool, wet summer following a winter with some hard frosts I feared that the ivy bees would not have survived. I was pessimistic, a very good number of males started emerging on 13th September, this is ten days later than last year. The first few days saw many males just buzzing around close to ground level looking for females. It was about a week later that females emerged and mating started. The mating period lasted another week, at the same time as new burrows were starting to be made. The weather was cool and wet so the amount of pollen around must have been much lower than previous years. Honey bees have apparently made 70% less honey than usual. In previous years there had been a period of 'Indian Summer' - a few days of warm sunshine, but not in 2012. The burrows seem to have moved into drier areas and the activity soon tailed off to a low level - instead of hundreds only a dozen or so ivy bees were seen. Like last year the activity ceased in the middle of October. I was able to mow the lawn again.

I've already posted a number of pictures, and there is not much to add. Here is one of an ivy bee on an ivy leaf.

Ivy bee,ivy leaf,Colletes hederae

A group hanging out in the lawn

Ivy bee,Colletes hederae

And a ball of males around a female.

Ivy bee,Colletes hederae

If you want to see the ball of bees 'in action' I have posted a video (8Mb to download) that you can pick up from here.

2013 Update

After the wet winter with a few sharp frost and a cold Spring I once again worried whether the ivy bees in my lawn will have made it through the winter. As they have moved in from the continent with warmer and drier climates it is quite conceivable that a bad winter will knock them back.

I needn't have worried, I first saw them on 5th September. They were staying close to a source of nectar, in this case a snowberry bush. There were a dozen or so. I presume these were males building up energy after they had emerged. It was only a week later that I saw them scanning the lawn in small groups, presumably looking out for the females to emerge. A week later the female ivy bees were out and the males were crowding around them as usual. In a few days the construction of new burrows had started. The weather was warm and dry, and the ivy flowers were out in some profusion. We had a cold spell around 10th October and activity tailed off quickly and I have not seen any in the last few days (19th October). It is a frenetic and brief life cycle, eleven months underground and one month of feverish activity.

Ivy bee,snowberry,Colletes hederae

The only extra observation I would add to previous years is that the area of burrowing was more restricted than last year. Last year they extended to new areas of the lawn further away from the edges. This year they stuck to the driest patches. I wonder whether this is because the larvae did not survive in the more open areas - with all the rain. The soil was very dry as in early October there had been an extended spell without rain, so the choice of burrowing location was not entirely based on current soil conditions, this would suggest the female ivy bees choose a spot close to where they emerged as that is the best proof that it is a good dry location. Based on the pattern of burrows it does seem to be dryness and then warmth that are the key criteria for choice of site.

Ivy bee,burrow,Colletes hederae

As they survived well so far I am pretty confidant they will be around in eleven months time. I hope to spend more time getting good shots of them burrowing next year. For more information about the spread of this species, please see BWARS site and the BBC Living World radio broadcast

2014 Update

I again waited to see if and when the ivy bees would emerge. Winter 2013 was extremely wet and mild and I wondered if this would have affected them. I noted the first single individual on 7th September and numbers grew in the following week as the males emerged. The date of emergence is very constant, and I wonder how they manage that. Their burrows are quite deep and they can have little idea of conditions above ground, I doubt they can monitor day length, so I guess they have a way of counting the days of the year.

I hoped to capture a large 'ball' of males around a female ivy bee but did not notice this happening this year - only a dozen or so males together. The rest of September was completely dry and warm and there was plenty of ivy around for them to feed and deposit down the burrows. In spite of the dryness the area covered by the burrows has not changed much, they prefer the loose soil which is close to large shrubs and only a few parts of the lawn, they do not seem to like shady places and the burrows have to be in sunnier parts. I have an apple tree that would I thought create good dry conditions near its trunk, but they do not choose areas close to it - perhaps they know there are too many roots to contend with?

The weather changed to cool and wet on 3rd October and by this time there were only about half a dozen females still actively digging burrows. With a lot of heavy rain, the ground is impossible for such small creatures to dig and the last one I saw was a week ago now (11th October). I wonder what happens to the bulk of the population. I am not sure what role the males have once they have mated, they are difficult to sex by just looking at them, although the females are generally larger than the males, I assume just the females dig the burrows and collect the ivy pollen for the next generation. There is also the issue is how they spread, do the female ivy bees disperse and try to find suitable locations elsewhere? To avoid inbreeding you would expect males to disperse to find females. As they mate as soon as the females emerge from the ground it would need exceptional sense of smell to detect a new colony elsewhere.

With so many pictures of ivy bees already, I have nothing much to add this year. With such a good September for them I am hoping for a bumper 2015.

Ivy bee,Colletes hederae

2015 Update

I started looking for emerging bees at the end of August, I scanned the ground and looked at the ivy flowers for pollinators and their nectar plants such as snowberry. There were one or two suspicious looking holes in the border of a top bed of the garden but no definite sightings until 6th September when I saw about a dozen ivy bees. The weather had remained cloudy and cool. In the next weeks the activity fluctuated with the weather. On warm sunny late mornings I saw up to 300 of them, as these are the ones milling around they must the males. The female ivy bees did not seem to be in evidence until 18th September when new burrows started to be excavated. The weather remained rather cool but dry for much of their active period, there were no really 'hot' days that we often have in early autumn. Burrowing activity continued but it seemed to be mainly at the top (driest and sunniest) section. Activity had almost petered out by 17th October so I mowed the lawn close to where they burrow but when the weather turned a bit warmer there were still a few (I saw 3 on 27th October) active. The last appearance was a record 31st October when we had some sun and warmth, the weather turned cooler and cloudy ever since and no more have been seen. In previous years a sharp frost brought an end to them, none this year

So although the weather has not been ideal - too cool - they seemed to have had a longer period of activity than average year. I have kept a lookout on local walks to see how they far they are spreading and am pleased to report to have seen them in three separate locations too far away to be members of my group, the ivy bees do seem to be prospering.

My photo for 2015 is of the actual mating event, it took quite a bit of time to get this shot. After the female is immersed in the ball of male ivy bees, one male succeeds in latching on, the pair then fly off some distance together.

Ivy bee,Colletes hederae