Sunday, 26 September 2010

Peeking under stones

Every now and then I lift some stones in the garden and check what's living under them. It is not a great strategy to observe bug behaviour, as the stone-lovers tend to be light-haters and rush frantically trying to hide again. However, this month it has turned out to be a good strategy to spot species I haven't blogged about yet. A large male earwig, Forficula auricularia, with its formidable pincers. Then, I disturbed the underground nest of some garden ants, Lasius niger. Although eggs and larvae couldn't be seen - probably too superficial for that - a tiny inhabitant of ant nests could be seen, some albino springtails, Cyphoderus albinus. If you click on the photo you will probably be able to make it out towards the left of the centre of the photo, next to an ant's head. Although easy to spot due to their white colour and highly mobility, their small size - probably no more than a mm in length -  made them quite tricky to photograph.
Finally, a couple of rove beetles (or Devil's Coach Man) Ocypus nero, one of them pictured below.
In addition, I found stones literally carpeted on rough woodlice, some earthworms and plenty of slugs.

Friday, 24 September 2010

Communal daddy long legs

These three daddy long legs (Opiliones), Paroligolophus agrestis, had found a cosy spot at the top of this apple. I am not aware that this species is particularly gregarious, although many daddy long legs do not dislike each others company and some actually form dense aggregations. The function of the social behaviour of daddy long legs is poorly understood and the explanations range from thermoregulation to defence. Although most individuals aggregating are adults, mating does not seem to explain this behaviour. The following video shows an instance of mass aggregation in Daddy long legs:

Tegenaria male

I have posted before on male Tegenaria spiders starting searching for females at this time of the year. I came across one this afternoon under the cat's bed. It has taken me a while but I am forcing myself more and more to use the flash, especially now that the days are shorter and strong natural light is a commodity we don't came across that often. With a built-in flash a straight macro shot gives a large shadow where the objective blocks the flash light, but I avoid this shadow falling on the target by first focusing on the target and tilting the camera to one side to shoot, and alternatively, by using the zoom. A bit of cropping and voila! shadow gone.

Tuesday, 21 September 2010

The late bumblebee

A sign that the bee season is coming to an end when the only bumblebees visiting the lavender are carder bees Bombus pascuorum. There might be still a few queens of the other species around, but this handsome ginger carder bee is still in peak season, making use of the late summer flowers around. This bumblebee has a relatively large tongue (average of 8.5 mm) which allows it to use deep flowers, even foxgloves (above, a worker in mid June leaving a foxgloves against the dark background of my rubbish bin) and Iris, as food sources.
Other than in Lavender, at this time of year, they can be seen foraging on Verbena bonairensisSedum spectabile, Agapanthus, Sunflowers, Caryopteris, Cytisus, Buddleia, Nasturtium, hardy Geranium, Salvia, Honeysuckle and Purple toadflax.
Males (above) and queens appear at the end of the summer and the species can be seen actively flying until the first frosts. They nest on the ground and actively comb moss to insulate their nests. For a little video of a B. pascuorum nest click here.

Monday, 20 September 2010

Celebrity flies

Continuing with the topical apple subject, I have been leaving damaged and rotten apples on the soil of a large pot. The place now is heaving with tiny fruit flies of the genus Drosophila - possibly the most famous and best known fly in biology, D. melanogaster. It is difficult to give an idea of how much research has been carried out using this fly but a quick search on the Google Scholar academic search engine yielded today under 3,000 hits on the common earwig, while D. melanogaster had 324,000 entries. Since the beginning of last century, experiments on fruit flies have generated much of the basic knowledge of genetics and evolution, and their genome sequence was published in 2000, before the human genome. Among the many reasons they have become such a popular model organism is that they are ubiquitous, easy to keep (who doesn't have fruit flies around the compost heap or fruit bowl?) and reproduce rapidly producing many eggs.
Much research has been carried out on fruit flies mating behaviour and the influence of genes on it. Despite their tiny size fruit flies can be easily watched performing their mating rituals on top of the rotting apples. Males are smaller and with a larger dark patch at the end of their abdomen. Females have a more stripy, and often distended abdomen.
According to Marla Sokolowski:

It might come as a surprise to some that D. melanogaster shows many exquisitely performed and complex patterns of behaviour. For example, the male fly shows courtship behaviour that is full of sensory stimuli and that requires the female to hear his song, feel his taps and licks, smell his odours and visually evaluate his stature...

As a primer, this figure (also from Sokolowski, 2001) illustrates the main steps of the fruit fly mating behaviour. Male 'song' is produced by wing vibration while keeping the wing tipped forward.

Check out the Drosophila melanogaster Wikipedia page for more info.

The lion springtail

Every day I go out in the garden and fetch the few apples that have fallen overnight. This springtail, Orchesella villosa, was resting on top of one today. It sat nicely for me and then jumped to pastures new.

Friday, 17 September 2010

Shiny red ladybirds and apples

We have been picking some apples today. Our tree is of the variety Red Devil and crops beautifully large sharp, tangy and red-fleshed apples. After picking one of them, we uncovered four 7-spot ladybirds nestled together, thinking themselves all ready for winter. They will have to look for a better spot as the apples won't be in the tree much longer. Ladybirds often overwinter in groups, but this is the largest group of 7 spots I've seen.

Sunday, 12 September 2010

September bugs

There is a definite autumnal feel these days. Shorter days, ripening berries and leaves already changing colour. September, however, is a month plentiful on all sorts of bugs. During a walk in our local Millennium Wood, Oppy Wood today, we spotted five butterfly species, Comma, Speckled Wood, Small Tortoiseshell, Red Admiral and Large White. We watched Commas and Speckled Woods sucking the sweet juice of ripe Blackberries.

There were plenty of Daddy Long Legs (tipulidae). Some of them mating.
A couple of Migrant Hawkers patrolled above our heads. A male (top) eventually stopped to rest, hanging from some low branches. He let me get really close to him for some shots.
There also were grasshoppers about - possibly Lesser Marsh Grasshopper, Chorthipphus albomarginatus - 7 spot ladybirds, froghoppers and wolf spiders.
A male Lesser Marsh Grasshopper

Friday, 10 September 2010

A forest bug

I realised a few days ago that I have not posted much about bugs (Hemiptera) in BugBlog. To start making amends, here comes a short one on a common bug these days, the forest bug Pentatoma rufipes, a quite large, showy shield bug easily to recognise for its spiky lateral thorax projections and orange legs. There are quite a few bug species about, many still nymphs, but an adult forest bug landed on my shoulder yesterday. Forest bugs lay their eggs on bark of oaks and other trees around this time of year and the nymphs hibernate on the trees. The adults are partly predatory. For lots of information and beautiful photos of British bugs here.

Hunter hunted

I feel like apologising for posting on Pholcus spiders again, but the reason is they are everywhere in my house. I read somewhere that hoovers are their most feared predators, but today I came across a chunky-looking spider, a mouse spider, Scotophaeus blackwalli (than you to No. 9 Spider from Wild About Britain for identifying it for me) holding a Pholcus on her fangs on the kitchen ceiling. I climbed on a stepladder to get some close shots, although I couldn't get as close as I wanted. The Pholcus' spindly legs stood aside while the mouse spider finished its meal. After a few minutes, the mouse spider left the Pholcus empty carcass behind. It made a change from the Pholcus being the usual spider predator in the house.
A side view from the mouse spider

For a beautifully filmed video of a house spider vs a Pholcus spider see

Saturday, 4 September 2010

Mummy long legs

My outside toilet is a Pholcus phalangioides haven. These long legged spiders hang upside down from every existing corner of it. One of them yesterday sat proudly over her 30 or so offspring. I had seen her in the same spot on previous days with her egg sac in her mouth, but this is the first time I see this spider's newborns. They are quite ghostly looking, with transparent legs and thorax, their dark eyes and brownish abdomens the only colour in them. This is a cropped image with a close up of some of the baby spiders.

Friday, 3 September 2010

Spider chat up lines

ResearchBlogging.orgIn summer and autumn, spiders become more noticeable. The tiny spiderlings born in the spring have now become adults and males are wandering in search of females. One of the most common spider species in the UK is the elegantly marked Linyphia triangularis (female above). This spider makes a sheet web with criss-crossing silk lines over it in low bushes and trees. The spider hangs belly up from the underneath the sheet. Flying insects colliding with the transversal lines  fall onto the sheet, where the spider traps them. Yesterday, while photographing 7-spot ladybirds I came across a pair of L. triangularis. The male made jerky movements with its chelicerae and palps and the female replied.

Male (on the left) and female Linyphia triangularis. Note the male's large fangs on the bottom photo.
Unfortunately, I seemed to have disturbed them and the male retreated, so I didn't see the end of the interaction. Field experiments carried out by Nielsen and Toft showed that male L. triangularis use what are known as 'alternative mating tactics'. Males guard subadult females just prior to their final molt in order to access them while they are still virgin, possibly due to a strong sperm preference which results in males mating with a virgin female fathering most of the female's subsequent offspring. These researchers took advantage of this behaviour and took 56 males and paired them with females in the field. Once this relationship was established they introduced an 'intruder' and recorded what happened up to the point when the female was mated. In 64% of the cases, the males resolved the dispute about the female by fighting using their large chelicerae. Larger males are better at winning these direct conflicts. But in 36% of cases, males used a different strategy called 'interference'. After losing a fight, they hang around and 'distract' the courting pair trying to chase the winning male away from the web. They actually succeeded and mated the female first in 7 occasions (12% of all conflicts) showing that this strategy - which is adopted by small males - can pay off. Additional observations suggest that smaller males hang around and try and mate with the female (not virgin at this stage) probably winning some residual paternity in the process.
 In a different study, Funke and Huber carried out detailed measurements of males and females genitalia and cheliceae (see figure above) and found out that male chelicerae (including the oversized fangs) grow faster with body size than genitalia, indicating strong directional natural selection on this trait due to the large effect on male-male conflict in their fights for females.

More information
S. Funke and B. A. Huber (2005). Allometry of Genitalia and Fighting Structures in Linyphia triangularis (Araneae, Linyphiidae) Journal of Arachnology, 870-872 DOI: 10.1636/S04-16.1

Nielsen, N and Toft, S (1990). Alternative male mating strategies in Linyphia triangularis (Araneae, Linyphiidae). Acta Zoologica Fennica