November bug magnets

I went for a walk this afternoon to re-acquaint myself with my clean and repaired camera. After spending almost three weeks camera-less, it was great to have it back. I just walked back to the spot where a few days ago I spotted the B. hypnorum and waited around the sweet smelling Mahonia bushes trying to spot more bumblebees. There were flies (Bluebottles and a smaller species) and wasps around, but my patience finally paid when I saw the distinctive large and dark shaped of a bumblebee amongst the flowers. Not a B. hypnorum, but a worker B. terrestris, stayed just for a few shots (top).

 The second bug magnet today was Ivy. There were dozens of male wasps feeding on Ivy flowers on the wildlife garden. Their large antenna reminded me of mountain Ibex males. I am not very good identifying wasps, although in a post in WAB today somebody pointed at a very informative webpage to identify them. I will update the post if I manage to get an ID. Around the ivy there were also feeding Bluebottles and a parasitoid wasp.
 The third bug magnet was a non-native bush related to the Ivy, the Fatsia japonica. Here the ubiquitous bluebottles were the only insects around.

Winter active bumblebees

We had our first frost yesterday, and it was also a frosty morning today. But coming back home this afternoon, with the light already going weaker, I came across a Tree Bumblebee, Bombus hypnorum feeding on a large Mahonia bush. I have posted before on this bumblebee, a recent natural colonist in the U.K. In the last two decades, reports of winter active bumblebees - mostly Bombus terrestris - have steadily been accumulating, especially in the south of Britain. Queen bumblebees are occasionally active in warm winter days, but the reports referred to queens collecting pollen - a sign they are actually nesting, not hibernating - or workers - indicative of active nests. These observations depart of the usual bumblebee life cycle in northern Europe, where winter hibernation of queens is the usual case. Whereas there are many native flowers in bloom during the winter to support a second generation in the Mediterranean, this is not the case in northern Europe. What resources are active winter bumblebees using? Stelzer and coleagues tested the hypothesis that winter bumblebees are making use of non-native flowers in parks and gardens. To do this, they set up B. terrestris colonies and followed them during two winters. In the second winter they introduced a new technique - micro-tagging - which allows automatic recording each time the tag passes nearby the tag reader set at the nest entrance. They attached the small RFID tags to the thorax of 64 individuals, and positioned a micro-balance at the entrance of the nest so that bumblebees also weighed themselves as they went in and out the nest, so that they can estimate the increase of weight of each bumblebee at the return of each foraging trip. Their results showed that bumblebees in their experimental nests were able to forage for nectar successfully during the winter, with nectar returns per hour foraging comparable or higher to yields obtained during spring and summer.

The researchers also carried out transects in the Royal Botanical Gardens in Kew to ascertain which plants were being visited by Bumblebees during the winter:
Only cultivated plants were in flower and the main plants visited by B. terrestris were Arbutus unedo and Salvia uliginosa in October (38.2% and 42.3% of the total recordings during that month, respectively), Arbutus spp. (A. unedo and A. x andrachnoides) (31.2%) and Mahonia spp. (Mahonia x media ‘Winter Sun’, Mahonia x media ‘Charity’ and Mahonia lomariifolia) (43.7%) in November, Mahonia spp. (69.0%) in December, Salix aegyptiaca in January (48.2%) and Lonicera fragrantissima (24.1%) in February.

The high yields obtained by the experimental bumblebees might be explained by the nectar sources being large bushes with large volumes of nectar per flower and the flowers being in large inflorescences, such as the ones in Mahonia (see photo above) and willows. In addition, there is no competition for nectar and pollen in the winter months by other foraging bees. Only a few honeybees were around, and these are not active below 10oC, while the bumblebees can forage at temperatures close to 0oC. Further work is necessary to assess if this generation is actually successful, that is, if males and queens are produced, but these results show how human impacts - gardening possibly coupled with climate change- have unexpected effects on the life cycles of native organisms.

Stelzer RJ, Chittka L, Carlton M, & Ings TC (2010). Winter active bumblebees (Bombus terrestris) achieve high foraging rates in urban Britain. PloS one, 5 (3) PMID: 20221445

Cameraless

I made the mistake of taking photos in a beach on a windy day (what was I thinking?!). You don't need to have much imagination to guess what happened. Some tiny grain of sand got in the camera and it stalled with the objective open, then, an ominous bleeping and a warning 'lens error! restart camera!'. After that, I did some frantic searches in Google to find a simple solution and failure to restart the camera after trying various tricks. The consequence, my Powershot G10 is being now sent to a repair centre, and while I wait, my dear old G6 was rescued from a cupboard and put to action. Now, when you get used to an upgrade you often do not notice the jump in quality, probably as you are often frustrated trying to get used to the new buttons and getting aquainted with you new toy. But going backwards, that's tough. I miss my G10 so much! I miss the image stabilization, I miss the large, bright LCD screen, the optical zoom, the top dial to adjust the aperture...

 However, I am so glad this happened at the beginning of november, when Bugblog is feeling a bit sleepy and cold, almost ready to hide under a curly leaf and go into hibernation. I would have been straight to the shops to get myself a G12 if this had happened in the summer. And still, some bugs still refuse to believe that, yes, it is cold and time to hide! While gardening this weekend, I was accompanied by the surprising buzzing of honeybees foraging on the fuschia, I disturbed a healthy female Tegenaria when moving a compost bag. I also came across this tiny snail, probably born only this summer, having a walkabout. Despite all of the above, when I saw the photo above I realised I can survive without my G10...at least for a few days.

Scary spider story

For a belated Halloween celebration how about some cannibalism on spiders? I have posted before on maternal behaviour in spiders, but, after coming across this species a few times in the last few days (a male above) I had to write on its bizarre, and utterly horrifying behaviour. Amaurobius are common spiders, with three British species which often live on holes in house and garden walls, fence posts or tree trunks. Their holes' entrance is surrounded by a characteristic radial and random web of white silk, with adheres to prey like velcro. These spiders are mainly nocturnal and can trap relatively large prey such as bees and droneflies, presumably as the sit nearby the entrance hole.

Amaurobius hole in a wall...

...and its owner with a trapped a dronefly

The unusual behaviour relates to reproduction. Females lay their egg clutch during June and July inside their holes and sit over it for three weeks, when she opens the egg sac and the spiderlings hatch. The interaction between the spiderlings and their mother stimulates her and inhibits the maturation of the eggs of a second clutch. The female is not agressive and instead solicits the young to migrate to her ventral side and lays immature eggs, the so called trophic eggs, for the spiderlings to eat. 

(from Kim and Roland 2000)

Spiderlings deprived of this extra food do not survive as well, and gain weight much more slowly. A few days later, the female dies and the spiderlings promptly cannibalize her, gaining further weight and increasing their chances of survival when they disperse. The trophic eggs are fertilized and apparently viable, so the female is actually increasing the survival of her first clutch by sacrificing a possible second. Does she produce more or less offspring overall as a result? Kim and Roland, in experiments in which they compared spiderlings with access to trophic eggs with deprived spiderlings, estimated that the mother produced an average of 104 viable spiderlings of the first clutch at day 6 when fed with trophic eggs, compared with a total number of 102 when they removed females from the first clutch and allowed to lay again. This similar number of total spiderlings is, however, misleading as six out of the 10 females removed from their offspring either had abortive clutches or ate them themselves, suggesting that the viability of the second clutch as a replacement clutch is decreasing and the eggs of the second clutch could be specialising in their function as trophic eggs. Trophic egg feeding might have evolved as a way of reducing intra-clutch cannibalism at a time in the spiderling's life when they cannot produce the sticky silk required to catch their own prey. Next time you see Amaurobius holes in your wall, spare a thought for these hair-raising behaviours happening so near you at night.

More information

Kim KW, & Roland C (2000). Trophic egg laying in the spider, Amaurobius ferox: mother-offspring interactions and functional value. Behavioural processes, 50 (1), 31-42 PMID: 10925034