Tuesday, 31 May 2016

Sharp-tail bees

It has been a while since I've seen a new bee in the garden. A couple of days ago it was sunny and warm and I watched the first male leaf-cutter bee Megachile willughbiella on a geranium. A while later a bee was basking on top of the fence post and I managed some distant shots. Its jaws looked very leaf-cutter like, but the end of the abdomen had some tell-tale spines, indicating it was a sharp-tailed bee Coelioxys sp. a bee I've only seen rarely in the local wildlife garden.
Although males and females sharp-tailed bees can be found nectaring at flower sources, they are cuckoo bees. The females do not collect pollen, instead, they are cleptoparasites, looking for ready made cells already provisioned with a pollen load. Their usual hosts are leaf-cutter bees, and their common name derives from their tapered abdomen of females, ending in a fine point, which is able to slice through the leaf wrappers of leaf-cutter bees, laying one egg either under the pollen load, or in between layers of the leaf wrapping of the cell before the cell is sealed. The cuckoo bee will also match the sex of her eggs to the host eggs sex, with the male eggs positioned in the outer cells of a nest. Once the larva hatches, they use their large mandibles to kill the host larvae or any other competitors. The cuckoos larvae complete their development and emerge at the same time as their hosts.
  I find the male abdominal spines very intriguing. What is their function? Coelioxys belong to the same family - Megachilidae - than Anthidium manicatum, the wool-carder bee, whose males are armed with formidable abdominal spines with a similar disposition. Male wool carder bees use these spines as weapons to defend their flower territory from other males and also other bees. They can fearlessly attack honeybees and large bumblebees, and are capable of killing them. It is unlikely that sharp-tailed bees use their spines in a similar way, as females do not collect pollen and there is no flower resources to defend. In the monograph Bees of the World, by Charles Michener, he hints at the spines being involved in dealing with the modified female's abdominal tip during copulation.
 There are eight species of sharp tailed bees in the UK, but in general they are very hard to identify without a specimen, so I will have to content myself with not having a definite identification for now.
 I have gone through my records of this genus in the wildlife garden, just five of them in June and July and here I show some record shots.
A male Coelioxys feeding on sage (12/6/10)
Female Coelioxys on birds-foot trefoil (4/6/2011).
Male Coelioxys resting. Many bees hold on with their mandibles in their sleep (10/7/2009).
Female Coelioxys on marjoram (2/7/2011).
Male Coelioxys on meadow cranesbill (11/7/2011).

Cuckoo bees tend to be rare bees, and sharp-tailed bees are no exception. The presence of cleptoparasites indicates a healthy host population. Often cleptoparasites decline and get locally extinct when a host population declines. In a study on sharp-tailed bees, about 3% of over 14,000 host cells (Megachile inermis) contained Coelioxys funeraria and less than 10% of Megachile relativa were parasitised. So, what about the hosts in my garden? The bee posts and bee hotels are commonly used by leaf-cutter bees of at least two species in my garden: Megachile willughbiella and Megachile centuncularis, used as hosts by several British Coelioxys species. Some species of Coelioxys are thought to parasitise Anthophora furcata, which is also a regular bee foraging and possibly nesting in the garden log piles. The synchrony of the hosts is remarkable as both male leaf-cutters and A. furcata, appeared in in garden in the last couple of days too.
This was the first of the year A. furcata in the garden, a male yesterday.
Male M. willughbiella, 29th May.
Male Megachile, possibly centuncularis, yesterday.

More information
Scott, V. L., Kelley, S. T., & Strickler, K. (2000). Reproductive biology of two Coelioxys cleptoparasites in relation to their Megachile hosts (Hymenoptera: Megachilidae). Annals of the Entomological Society of America, 93(4), 941-948.

Michener, Charles Duncan. The bees of the world. Vol. 1. JHU Press, 2000.

Falk, Steven and Richard Lewington 2015. Field guide to the Bees of Great Britain and Ireland. Bloomsbury, London. 432 pp.

Saturday, 16 April 2016

Massive rainbow worm emergence

I woke up early this morning and went for a walk around the park. It was cold and it had rained a lot in the night. I had to watch my step as there were hundreds of blue-grey worms, Octolasion cyaneum, on the pavements and ground. This is a very colourful and common earthworm species, easily recognised by its yellow tail end and its orange clitellum (the central raised band) when adult. They are sluggish, live in topsoil and commonly emerge in large numbers after rain. Some individuals were the largest I've ever seen, over 26 cm! (bottom shot), although around 15 cm was much more common. I was surprised there weren't more blackbirds and thrushes feeding on this worm bonanza! Why do they come up in the rain? Reproduction can be ruled out as this species is parthenogenetic, that is, they can reproduce on their own, producing genetically identical offspring. Populations have little diversity and are made or clonal lines. Adult worms lay cocoons in the soil that contain singletons or twins.
More information
Lowe, Christopher N., and Kevin R. Butt. Life cycle traits of the parthenogenetic earthworm Octolasion cyaneum (Savigny, 1826). European Journal of Soil Biology 44.5 (2008): 541-544.

Monday, 14 March 2016

My conservatory spiders

The sun has been shining for a couple of days and it was warm enough that I started taking plants out of the conservatory into the garden and having a little tidying up. While doing this, I found a few spiders. Many were very tiny, very young individuals that I was unable to photograph properly and identify. Others were quite impressive. They have survived the winter in the dry, not too cold environment of the conservatory.
 First up, a Steatoda bipunctata, a false widow spider, which was on the side of a pot, a fully grown female. It has a very tick-like appearance, especially when it drops and tucks its legs in.
In between the bags of compost, I noticed the sheet webs of a Tegenaria. Here she is a bit camera shy, but shows her pretty abdominal patterns.
A few cob-webs came out of a corner, and then a Pholcus phalangioides ambled around trying to settle again.
This slim, fast and jumpy male Clubiona which I call black-face (possibly C. terrestris, but pedipalp examination is needed to confirm species) also featured on the top shot, fell from the foliage of a pot plant.
Finally, a Pardosa wolf spider on the window frame. There are dozens of young pardosa that have overwintered outside and sunbathe in loose groups on tiles and stones just outside the conservatory. This one got in through the crack of the window.

Wednesday, 27 January 2016

Winter active spiders in the house

We are having an exceptionally mild winter and, although much of the time it is wet and dull, winter invertebrates respond to the prevailing conditions. While some spiders overwinter in the safely of an egg sac, or as tiny spiderlings on leaf litter and tree trunks, others winter as grown young or adults. In warm conditions, some of these species overwintering as grown spiders continue to be active through the winter months, hunting or looking for mates. This post was prompted by a silky, silvery mouse spider Scotophaeus, that I found on the kitchen ceiling in the morning (above). So, I decided to investigate which other spiders were about inside and outside of the house. All the photos taken this morning.
Pholcus phalangioides.
The Pholcus spiders in my outside toilet, which is not heated, have been much more active than it is usual in winter. Pholcus adopts a curious flat position in cold conditions, but a large individual has been changing corners and looks gravid, or indeed very well fed.
Amaurobius similis with centipede prey
 In a crack at the bottom of the toilet door lives an Amaurobius similis. A couple of weeks ago I watched as a large springtail, Orchesella villosa, tripped one of her woolly silk lines. The spider sprung out like lightning out of her retreat, but the springtail, making use of its wonderful jumping abilities, escaped unharmed. Today the spider was luckier. I noticed she was out, which is unusual, and looking closer I saw she was busy with prey: a centipede, likely Cryptops hortensis.
What other spiders are out and about?
Inside the kitchen window, a mid-size garden orb-weaver Araneus diadematus, hung from her web. They occasionally wander inside and live on small plant midges or drosophila from the fruit bowl. Females have occasionally reached full size inside the house and attracted males.
A poor shot of an Araneus diadematus inside the house.
Zygiella x-notata legs visible touching its web.
On the sheltered top corners of windowsills you might find Zygiella x-notata, the missing sector spider, in a silky retreat, often next of her egg sacs and the empty wrapping, one of her front legs touching the guide thread to the center of her web. At night she comes out and sits in the middle of her web. They are active regardless the weather, building their new webs early in the morning even in hard frost.

Sunday, 15 November 2015

Wandering male lace weavers

In the last week I have found two different males Amaurobius similis wandering, one in the porch and the other in the house. Note the different abdominal pattern in the photos below, especially the dark blotches surrounding the cardiac mark (the midline elongated area over the abdomen). In this species, mature males are most likely to be found between September and November, and they abandon their webs in search of the female retreats. I released them both after taking their photo paying especial attention to the palp (above), which is diagnostic and separates this species from the similar one A. fenestralis. Males A. similis have an inward pointing, curved sharp projection on its palp, which in A. fenestralis is thicker and blunt.
Male 10/11/15.
Male 15/11/15.