Araneidae: typical orb weavers

It's #arachtober, a whole month dedicated to the celebration of spider awesomeness and diversity! For this reason, I will be writing a daily post on the natural history of a British spider family.

For the first post, I have chosen Araneidae, the typical orb weavers. This is one of the largest spider families and include many familiar species, such as the garden spider (Araneus diadematus), the window frame spider, Zygiella X-notata, the wasp spider Argiope bruennichi, and the small cucumber spider Araniella sp. There are 33 species in the UK.  The drawing on the left shows the eye arrangement in the family (based on a photograph by Kiron Basu)

In foggy weather, orb webs become very visible, heavy with dew. The spider is sitting in the central hub.

A. diadematus spinning its web.

The spider's web
The most characteristic feature of araneids is that they spin flat, rounded webs with radial threads connected by a spiral net-like pattern of threads, which they attach to vegetation or other structures  The threads are sticky, and able to trap flying insects. The spider either sits in the middle of the web (often at night) or hides in a retreat on a corner of the web, with one of their legs touching a signal thread connected to the hub of the web, which allows them to detect the vibrations produced by any struggling insects. Orb spiders often eat their web at the end of the day, and build a new one in the morning. As they adopt a sit and wait strategy to catch prey it is easy to find particular individuals in the same spot every day.

Dangerously close. The male (on the left) was dispatched before he had the chance to mate, after a lengthy and careful approach.

Mating and cannibalism
Adult females are readily distinguished by their larger size and swollen abdomen. Females often cannibalise males (often right during mating), and males might die after mating a couple of times so at the end of the season, only mature females might remain.

Female Araneus diadematus with its fresh egg sac.  Once their egg sac is finished, the female sits on it and will die in a few days.

Egg sacs and spiderlings
Females lay their eggs, often over a thousand of them, and spin an egg sac around them. Females might die shortly after egg laying. The spiderlings hatch, moult inside the egg sac and then they emerge. In some species, like the garden spider, they spin a communal web and cluster together in it until they are ready to disperse.

A spiderling ball, newly born A. diadematus

At the end of the summer, full size Araneus diadematus can subdue quite large insects such as droneflies, butterflies and wasps.

A. diadematus are very variable in background colour with a range from sandy to chocolate brown, although the white markings on the abdomen tend to be more uniform.

A spider safari

Today for 30 days wild we did a spider safari. Any day is as good as the next for spiders if you ask me, but I am aware there are many people either fearful or wary of spiders. If you are in either of those categories, thank you for reading on, I hope that at the end of the post you look at them for the wonderful and diverse group they are and by understanding them better you might keep a certain level of respect for them, but enjoy them more. All the photos were taken today.
 My daughter found a large cluster of Garden Orb Spider Araneus diadematus spiderlings in between two pots (above). These spiderlings balls are now everywhere (even on my car!). Once they hatch from their silky cocoon, they will stay in a tight ball for a few days in a communal web. After they moult they will disperse to make their individual webs and start catching tiny insects, mostly aphids.
 There are two age groups of Araneus in the garden now. The tiny newborn spiderlings and the year old spiders which have survived the winter and are not mature. This large male has built its web in a flowering sage with is always busy with insects.

Male Araneus diadematus on his web.

A male Philodromus aureolus

 We also found this lovely spider crawling on a hedge, on our way back from school. Males of some crab spiders have iridescent scales on their bodies. I think this is Philodromus aureolus. After failing to take a photos where it was as it was quite mobile, I potted it to photograph at home. Shortly after I released him in the garden I found another individual on ivy, and what could possibly be the female of the same species (below). Crab spiders don't build webs, instead sitting on leaves or flowers to ambush flying insects that stop to bask or feed on the flowers.There are several common Philodromus species, and without microscopic examination of their genitals (or palps in the case of males) identification to species is not possible, which is sadly true for many species of spider.

A female Philodromus sp.

 I searched on some bare ground in the garden and didn't take long to find a wolf spider, a Pardosa, (probably amentata). Wolf spiders don't build webs either, but they move about searching for insects, although they also do quite a lot of basking on sunny spots on the ground. As they don't have a 'home' females carry their egg sacs with them attached to their abdomen, which you can see in the photo below. This photo also illustrates the maternal behaviour of spiders: many species build a cocoon for their eggs, which they attach to a dry corner, or carry the egg sacs with them, or the spiderlings (wolf spiders do this!) or even feed the spiderligs with eggs, regurgitated prey or especial eggs. The most extreme form of maternal behaviour is matriphagy, in which the mother allows the spiderlings to eat her, and eventually kill her.

Female wolf spider, Pardosa sp., with her egg sac.

 Another favourite place for spiders is the log pile. I removed a few logs and found a Blue Lace Spider, Amaurobius similis. A spider that forms a very characteristic form of carded silk and can be found on crevices on walls or trunks or on thick ivy. Amaurobius is one of the bunch of species in which females sacrifice themselves to their first batch of spiderlings, a matriphagous species.

Amaurobius similis. 

 And a few logs later a large female House Spider, Tegenaria sp. House spiders built sheet webs funnelling into corners, where they have a retreat. When potential prey lands on the sheet they come out and trap them. You can entice them to come out by spraying some water on the sheet web. If you see a large spider with long legs in the autumn running around on your living room carpet, or you find one in the bath in the morning they are likely to be a male Tegenaria. They have abandoned their retreats and go about searching for mature females to mate.

Female Tegenaria sp.

 Then it was time to go inside. I have a thriving Pholcus phalangiodes (known as Daddy Long Leg spiders) population in the house. They hang from corners in the ceiling, not moving much. This mature female, which lives under a shelf in the toilet, with her distended abdomen, looks ready to lay her eggs. She will wrap them loosely with silk and carry them in her mouth until they hatch. Then she will sit by her spiderlings for two weeks (presumably not eating anything during this time). Despite their spindly appearance, Pholcus are fearsome predators, capable of subduing much larger and stronger spiders by wrapping them in silk with their long legs.

Pholcus phalangioides, mature female.

Motherly candy-striped spiders

I find maternal behaviour of spiders fascinating, and I keep an eye for it whenever the opportunity arises. When repotting my gingko bonsai on the 2nd of September, I noticed a couple of rolled leaves. They contained web shelters of Candy Striped Spiders Enoplognatha ovata/latimana. One of them had a female with her egg sac, the other already contained spiderlings (above). I checked today again, both females were guarding their spiderlings. The first one approached the entrance of her leaf to check what was causing the disturbance, the spiderlings clustering together like Araneus spiderling balls. The spiderlings have been in one of the nests for almost two weeks. Will the presence of their mother increase their chances of survival? will the mother feed during this time? In the related genus Theridion (Enoplognatha ovata was previoulsy called Theridion ovatum) the presence of the mother guarding the egg sac appears necessary for egg survival (although there were some loses due to parasitism from a tiny wasp). The mother not only sits near the egg sac, attached to her by a silk thread, but she is on the alert, and will move the egg sac to the centre of the web when predators are nearby. Unguarded egg sacs are rapidly predated by insects (ants, earwigs) and other spiders. And what about the spiderlings? what do they have to gain from their mother's care? In the Happy Face Spider, Theridion grallator, the female loosens the egg sac allowing the emergence of the spiderlings, and then captures prey for her brood. The spiderlings are under the female care up to three months, until they disperse and feed on their own. The female might produce another egg sac if the first one is lost, but she will die by the end of September early October. The spiderlings will disperse and overwinter near the ground.

One of the females, in close contact with her egg sac (2/9/14)

More information

British Arachnological Society.

Newborn Pholcus spider

A female Pholcus phalangiodes carrying eggs has been in the outside toilet for over two weeks. Today, I noticed her shuffling a bit, and when I looked, the first spiderling had been born and was sitting on the eggs. The spiderlings' folded legs and rows of eyes are clearly visible through the egg shells. When I returned five hours later, the female was holding a fuzzy ball of baby spiderlings.

For more on Pholcus on BugBlog click here.

Spider scrum

I bet it is hard to find a higher leg density than in a freshly born ball of spiderlings. These 30 or so Pholcus phalangioides spiderlings hatched last night on the ceiling of my outside toilet, about 240 legs in just a few cubic millimeters. In the morning they were still clutching each other and their empty egg sac. By today's afternoon, they had arranged themselves under the vigilant eye of mum as in my previous post.

Dispersing Pholcus babies and the spider man

A few months back, I bought a tattered copy of the classic The World of Spiders, by W.S. Bristowe, the 38th book of the New Naturalist series. This book is a wonderful read and I recommend it to any spider enthusiast. Bristowe was in awe of spiders from an early age. He describes being greatly puzzled -  when he was able to read -  and after devouring any spider book he could get hold off, that

the great experts seemed to leave off where I wanted to begin. They had described with precision the appearence of the corpses, in words often unfamiliar to me, and had left to other people the task of writing about their habits

His book does not disappoint as he went on to describe the behaviour of many familiar and unfamiliar spiders with their own observations, displaying the author's never ending curiosity for the world of spiders. The book has photos (black and white and colour) and astonishingly beautiful line drawings by Arthur Smith, often portraying his subjects going about their business and demonstrating an incredible attention to detail. Bristowe describes his first meeting with Smith in the preface of the book:

he ended the afternoon perched on a table with a torch under one armpit whilst he busied himself with pencil and paper sketching a Pholcus on the ceiling.

Bristowe seemed to have a particular fascination with Pholcus phalangioides, the daddy long legs spider.

Pholcus did not live in my childhood home at Stoke d'Abernon, Surrey, although she thrived elsewhere only about ten miles further, so the quest of an explanation inspired me to trace her distribution. This had to await the acquisition of a motor-bycicle and then, with the impudence of youth, I zigg-zagged across England ostensibly seeking rooms in hotels or lodgings whose ceilings I viewed with nonchalant interest. My apologies are no doubt due to a host of hoteliers for gaining entry under false pretences...

 On the 23rd of August I noticed that the eggs from an egg sac a Pholcus phalangiodes female in the toilet had been holding had hatched. She was still holding the empty egg sac (above), and twenty-two  spiderlings hung still, upside down around her. In Bristowe's words:

The eggs may hatch in two or three weeks' time and the young then hang motionless like washing on clothes-lines for the next week or fortnight during which time they take no notice of any disturbance such as those caused by their mother catching an insect. Unlike nearly all other spiders, they do not molt until after they have emerged from the egg-sac.
  Directly they have recovered from this first molt they gradually begin to migrate, taking positions further and further along the wall and spacing themselves as though they had staked their claims to particular territories. Now they are interested in food and for several of them their first meal is of a brother or sister who is backward in his timetable of who dies or is injured as a result of the delicate operation of moulting.

A couple of days ago the spiderlings moulted and today, at the tender age of 12 days, some more adventurous spiderlings have started to explore and disperse away from their mother, their old skins hanging like ghostly gloves from the invisible web.

More information
Bristowe, W.S. 1958. The World of Spiders. The New Naturalist. Collins, 304 pp.

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

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.