Pollen gathering spiders

If you go out into the garden and search for orb webs amongst the bushes, you are likely to surprise a garden spider holding onto a fly, an aphid or other small insect tightly wrapped on silk. In the autumn, when they are at their largest, they will be able to subdue large prey including butterflies and droneflies. Indeed, spiders are generally known as predators and the purpose of the almost invisible orb web is to trap flying insects with the sticky droplets that cover the silk threads, right? Orb spiders, including the common garden spiders, Araneus diadematus, have challenged this assumption. When garden spiders hatch in spring, and after spending a few days in a tight ball with their siblings, the tiny, millimetre long spiderlings will disperse and make their first orb web (top shot). Until then, they have been living of the yolk from their egg stage, but now they have to find food. At that time of the year there are not many flying insects, and spiderling mortality due to starvation is high.

Young orb weaver, Zygiella sp, with an aphid prey.

  Now, when you look at a spider web under the microscope you can see not only insects and other small invertebrates trapped on it, but also pollen grains and fungal spores. In spring there is an abundance of pollen of wind pollinated flowers and trees. Given that orb spiders rebuild their web at regular intervals, pulling down and eating the web before spinning a new one, the young spiders could potentially be feeding on the pollen collected, benefiting of this plentiful resource. Risa Smith and Thomas Mommsen, from the University of British Columbia and Dalhousie University carried laboratory experiments to test exactly this. They compared the survival and web building frequency of individually housed spiderling, which were fed exclusivelly on birch pollen or fungal spores with unfed controls and spiderlings fed on aphids. Their results show that spiderlings not only feed on the pollen, but pollen feeding increases their survival compared to starved spiderlings or spiderlings given fungal spores. however, only the spiderlings fed on aphids moulted into the next instar. Smith and Mommsen reckoned that given that pollen from wind pollinated trees is highly deficient in the aminoacid tyrosine, essential for cuticle formation, spiderlings could be unable to thrive only on pollen, but would need to capture the occasional insect to moult into the next stage. The researchers noted that pollen grains are too large to be consumed whole by the spider, therefore, they couldn't have been accidentally swallowed. The spider indeed treated pollen grains like insect prey: grabbing the pollen grain, dissolving a hole in its coating and sucking the contents! More recent experiments estimate, using isotopes, that about 25% of the diet of young orb weaving spiders can be made of pollen. Spiders might be best considered omnivores rather than carnivores!

More information
Smith, R. B. & Mommsen, T. P. Pollen feeding in an orb-weaving spider. Science 226, 1330–1332 (1984).

Eggs, B. & Sanders, D. Herbivory in spiders: the importance of pollen for orb-weavers. PLoS One 8, e82637 (2013).

Thanks to Robert Jaques for sharing the paper that started this blog.

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.

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.

Three bright characters for the end of August

Some invertebrates appear as heralds of autumn, and today three striking ones were present in the garden. Migrant Hawkers have been around for a while, forming loose swarms that hunt between 2 and 8 m high, often well away from water. In the cooler, shorter days of late summer it becomes easier to come across sunbathing ones, perched on a branch, often more than one near each other. I flushed this male a few times as I went about in the garden, until I finally spotted him hanging from its perch. I got so close taking the macro above that I could have kissed him.

A single Red Admiral was also about, alternating between feeding in the buddleia and basking on a brick wall. During sunny spells she closed its wings, while during passing clouds she revealed its fresh, amazingly marked wings to their full splendor. This was a beautifully marked individual, the small, delicate blue markings on the edge of its wings very apparent.

I used the flash to counteract the sunshine and reveal the intricate patterning of the underwings, which can make the butterfly well camouflaged.

This garden spider, Araneus diadematus, is one of the largest in the garden, she hangs her web on the side of the rubbish bin, and has her retreat under the rim. Given the size of this species, detailed inspection of the epigyne is possible without even disturbing the spider (click on the photo to see it).

Male garden spider

We found this male garden spider, Araneus diadematus, on our garden gate, actively walking about. Male garden spiders are on the lookout for females in August and September, when they become adult and receptive. This was a large and handsomely marked male, so I gave it a session on the white bowl and then released him near the largest female in the garden.

Drinking spider

The sky was clear of clouds and the temperatures have come down in the night. A dew covers everything in the garden, including a female garden spider, Araneus diadematus, with a large, distended abdomen, nearly ready to lay eggs. She is hiding under her dry leaf retreat on the honeysuckle, and using her rear legs to collect the dropplets of dew on her abdomen. She repeatedly makes a brushing motion and then licks the tip of her leg.

Male garden spiders out on a mission

Even my four year old has noticed that there are lots of spiders about. She found many fresh webs by Araneus diadematus today, and she asked why are there so many now. I tried to explain that they have grown large recently, and that's why we are seeing them more easily, but she discarded this and came up with her own explanation: is her watering the plants yesterday what must have made them grow. Female Araneus diadematus are reaching quite large sizes now, although there is a lot of size variation. The record holder in our garden sits by two rubbish bins, and has probably been gorging on the flies the rubbish attracts. Males have also reached adulthood and, in contrast to the sit-and-wait females, are moving between bushes in search of receptive females. I have come across three in the last few days. They have slimmer abdomens and robust legs and their palps are quite noticeable. The male must be careful, though, as females will quickly make a meal of him if he does not reach their high standards. I found this male getting closer to a small female's web. As he was on a broom, focusing him was very tricky and I resorted to trying the white bowl.

A wrapped up genetic legacy

There are still fresh garden spider webs around if you look, with large Araneus diadematus females making the best of the mild weather. Many, though, have now died, exhausted and shriveled up, after laying eggs. This genetic legacy to next year generation is now inside wrapped up in a yellow silken cocoon attached a corner sheltered from the rain. After finishing their cocoon, they sit on it until they died, not bothering to make a web any more. The eggs will overwinter inside the sac and the spiderlings will emerge the next spring.

30 October 2011, female spider on her egg sac.

Spiderling Balls

From the end of April to June you may come across a strange ball-shaped object on a bush or a fence. If there is the smallest disturbance, the object disintegrates coming apart in all directions. It is then you realise that the object was a congregation of Garden Spider or Cross Spider (Araneus diadematus) spiderlings. Garden spiders lay several hundred eggs and wrap them together in a silky cocoon in the autumn. Hatchlings moult once when still inside their silky cocoon and, after a week they follow each other out of it. Spiderlings have a strong aggregation instinct, they still have large abdominal yolk reserves and do not eat for a few days. Instead, they make a communal web by weaving threads upwards of the cocoon and hug each other in a tight ball in the middle of the web until all their yolk is reabsorbed. With time they become more aggressive to each other and they start their independent, solitary lives.
Why do they get together like this? does this behaviour give them some advantage early in their lives?
Experiments revealed that spiderlings can survive and make normal webs when reared in isolation. Although communality does not seem necessary for survival, communally reared spiderlings survival rates were higher than spiderlings reared in isolation. High air humidities made spiderlings came closer together in their communal webs: this could be an adaptation to avoid becaming trapped in water dropplets in the rain when isolated which can easily result in drowning for such small animals. The communal behaviour could also offer protection against predators: all spiderlings sitting in the middle of a radial web is a very good sensory device that could provide them an early warning system for approaching predators, especially when coupled with their surprising explosive dispersal reaction to minimum disturbance.
When the air was dry and the yolk has been absorbed, spiderlings came apart from each other, and it is in such dry conditions that spiderlings make a long silk thread that allows them to balloon in the air and disperse from their natal place.

This is the cocoon spiderlings emerged from

Spiderling ball. The communal web is just visible

The spiderlings felt a little gust of air -from my breathing near them when taking the photo above - and rapidly came apart. 

More information

Burch, T . L . 1979. The importance of communal experience to survival for spiderlings of Araneus diadematus (Araneae : Araneidae). J . Arachnol . 7 :1-18 . here.

Giant garden spider

Some individual garden spiders, familiarly installed in strategic spots in the garden have disappeared in the last weeks, probably after laying their eggs and spinning a cocoon around them in a safe, dry corner. I came across this magnificent female, going on a walkabout. The largests I've seen (a 1 p coin for comparison).

Life and Death

A butterfly day: Small Tortoiseshells, Red Admirals and Painted Ladies sunbathing in the morning and gorging on the buddleia blooms; Speckled Wood in their never ending spiral flights. Same old same old. I witnessed more dramatic things though. A Small Tortoiseshell left the spot on the ground where it was sunbathing and flew straight onto the middle of a large garden spider web. The spider quickly grabbed it from below, while the butterfly frantically fluttered trying to get away. The fight continued for a minute or so, then the butterfly started to flutter more and more slowly until it gave up. I didn't have my camera with me (I though I did but it was only the case, doh!) so I returned later and tried to find it. Here it is, the full spider holding onto its neat small tortoiseshell meal or the remains of it.

 

As I was leaving the spider, two common blues, a female with a male closely following her, fluttered by my head. I watched. They looked like they wanted to settle, flying low amongst the bushes, and after a bit they did, on some marjoram. They rapidly took positions facing away from each other, closed their wings and mated.

The end of summer

Autumn is quickly approaching. The leaves on some lime branches are already yellow and a few brown leaves rustle on the ground. The squirrels have dropped some early conkers they have nibbled. But today is a bright, warm day, with lots of butterflies. A Speckled Wood was sunning itself in the park and a Comma, a Small White and a Large White visited the garden in the morning.

We walked past one of the last buddleias in good bloom. It is now the end of the buddleia flowering season and this particular bush teems with butterflies today. I count six Red Admirals (probably already migrating south) , three Small Tortoiseshells (ready to hibernate) and a Large White.

One Small Tortoishell fed on the dandelions amongst the grass.

Other insects included a queen Bombus lapidarius, velvety black and red feeding on Agapanthus, and B. pascuorum, the most common bumblebee these days, on Sedum spectabile (below).

Lots of Araneus diadematus. One five-legged male creeps close to a female's web.

Another female nearby spins its web.

The large ivy is not flowering yet, although it's got lots of buds.