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.

The cost of long-horned moths long antennae?

As I walked past the university woodland area, in the usual clearing, a swarm of 7-8 Yellow-barred Long-horn moths, Nemophora degeerella in their bobbing flight. A few other males sat on the leaves facing the swarm. I searched for females to no avail, but something caught my eye, a male that had been caught in a spider web by his antennae (top shot), still alive, but kicking hopelessly. I have covered these moths in previous posts, the extraordinary antennae of their names only applies to males: the females have a much shorter antennae. This sexual dimorphism suggests that the male's antennae have evolved in response to sexual selection, possibly in relation to pheromone detection by males.

Two males rest on leaves (1/06/2017).

The evolution of exaggerated sexually-selected traits often is accompanied by costs and in the case of these moths, increased predation risk is a likely prize the males are paying for their oversized antennae.

A large swarm of long horned moths on 1/06/17.

Hawthorn shieldbug and garden spiders

 At this time of year it is hard not to notice Araneus diadematus, the garden spider. You walk through their orb webs when walking on paths with many hanging by each other by the dozens in front gardens. Most of the individuals you see on their webs now are females. Males have reached maturity and forgot about feeding: mating is the only thing in their mind, so they move across stealthily, in search of just mature fertile females. Many of the females are now just growing their eggs, fattening up, feeding on the many insects still flying in the mild september. The one above got a Hawthorn Shieldbug and rapidly rolled it up with silk, biting it repeatedly. The stink of the bug seems not to bother the spider. It was a dry afternoon, so the tiny dropplets visible on the silk threads on the bottom-left corner of the photo are probably the glue what makes the web sticky.
 I have been photographing garden spiders in the last few days. They are an easy subject. You can find the same individuals day after day in the same spot and you can get very close without disturbing them.

I tried a white background with this one, placing a white card behind the spider outside.

This is the largest spider around, in a very leafy front garden.

Hunting wasps

There are few things reminding me more of the end of summer than hunting wasps. Today, a buzzing ball of fury fell on the pavement in front of me. A common wasp, Vespula vulgaris, holding on a male Eristalis dronefly, desperately trying to escape. The wasp held onto the dronefly's legs, chewing three of them and a wing off, and rendering the dronefly defenceless.

A loose leg and a wing are visible

I was amazed by the determination of the wasp, which was thrown about by the hoverfly while it was only holding by the hoverfly's abdomen.A very short clip shows moments after they landed.

Crab spider stalking fly

I spotted this crab spider in my local wildlife garden, it had this strange clock-work movement and grabbed my attention. Then I spotted the fly. The crab spider, a female Xysticus cristatus, legs outstretched, on the left of the photo. The large fly is on the right, having fed or drank from the base of a teasel leaf. If you want to know what happened next see this video.

Elder aphid networks

The photo above shows a dense colony of Elder aphids, Aphis sambuci, many individuals of different ages feeding close together. They are likely to be all a clone, female descendants of a single founding female that emerged from an egg early in spring, and identical genetic copies of her. Elder aphids forms this characteristic ash grey patches on tender elder stems. The aphids suck the elder sap using their piercing mouthparts. Having a close look at elder aphids gives you an opportunity to learn to learn about ecological networks in a few minutes of observation. All the photos in this post were taken in the space of seven minutes this morning on my way to work on the same young elder bush.

 Despite the fact that elder, Sambucus nigra, has relatively few insect predators, most likely due to it having cyanogenic chemicals in its leaves, elder aphids are an important link in networks making use of elder sap. 

Ants have a mutualistic relationship with the aphids. They benefit from the aphids honeydew by soliciting them to excrete it, taping them with their antennae. The sugary rich liquid is consumed by the ants and their larvae. The ants treat the aphids as their domestic animals. The aphids benefit too, as potential predators or parasites are pursued or attacked by the ants.

But the ants can't totally defend the aphids from their numerous predators. Here a female hoverfly, Epistrophe eligans, lays eggs on a patch of elder aphids.

A hoverfly egg is visible on the centre of this photo, on the edge of the aphid colony.

See the patches cleared of aphids in this patch? They are due to predation by the green hoverfly larvae just visible amongst them. Surrounded by food, the larvae will gorge on the aphids and grow rapidly.

This hoverfly larvae (possibly Epistrophe eligans) is likely to be ready to pupate.

Not only hoverflies, ladybirds are attracted by this aphid bonanza and adults land on the elder, possibly attracted by the smell of aphids. A Harlequin sunnies itself on a leaf...

...while an active 2 spot searches about.

Ladybirds have laid their bright yellow egg clutches on or under the leaves, near the aphid colonies.

...here visible on the background. I couldn't find any ladybird larvae today on this elder. 

This fly enjoyed licking the honeydew on a leaf. Some species of butterflies, like the Speckled Wood, also takes advantage of honeydew.

Five species (2 ladybirds, a fly, an ant and a hoverfly) thriving on elder aphids. If I had waited a bit longer, or being a bit luckier, I could have witnessed tiny parasitoid wasps that lay their eggs inside the aphids and eat them from the inside!

Dapper spider

Unfailingly, house spiders, Tegenaria sp. males go on a walkabout this time of year looking for females. This male sat on our outside wall for a couple of days, all exposed. Love is a dangerous affair for spiders. After their last moult, when they reach maturity, they move often in the open, away from its silky shelter, where predation is more likely. This same week, flocks of Long Tailed Tits, and Coal Tits have roamed the garden, the latter paying special attention to walls, poking into holes while deftly holding onto the wall.

Queens and kings on the wing!

We've enjoyed a whole week of warm weather and no rain. Today, garden ant queen, Lasius niger,  that had already lost its wings, was running on the pavement, and on my local wildlife garden, nervous workers on the path made me look closer. When new winged queens and male ants are ready to emerge, workers follow them run frantically about. And emerging they were, for at least the third time this year, many queens and smaller numbers of male ants. Some queens were trying, unsuccessfully to fly straight from the ground, others, like the one above, reached for a higher point, to get a better chance to take to the wing.

Winged ant queen, Lasius niger, revving its wings on the ground

The couple of queens above started climbing a fence post while the workers followed them. Although many winged ants will eventually take to the sky, where they find their mates, a Zygiella x-notata web hung with entangled winged ants on top of this fence post. That spider is going to have a super dinner tonight.

 I have never seen flying ants this late in the year, have you seen any winged ants recently? The Society of Biology is carrying out a Flying ant Survey, where you can submit your records.

Night pollinators

Although daytime pollinators get a lot of press, night time pollinators are important too. Many moths feed on flowers at night, and some species of flowers appear to have evolved to be pollinated mainly by moths. If you go out to the garden on balmy summer nights, such as the ones we are enjoying this early September, you are likely to see Silver Y, Autographa gamma, feeding. This lively moth looks like a blur as it flutters continuously while it feeds - the flash creates a false 'frozen' effect. Like another summer visitor the Hummingbird Hawkmoth, the Silver Y has a very long tongue which allows it to feed on Honeysuckle, Lavender, buddleia, peas and wallflowers (above). All photos taken yesterday and today in the garden.

on honeysuckle

on lavender

...and on wallflower Erysimum Bowles Mauve

 And they must be careful on their comings and goings, while flying above them, Pipistrelle bats are hunting...

Drama under the barbeque

This morning, while watching the hoverflies feeding on the fennel I realised I wasn't the only one interested in them. A female digger wasp Ectemnius, was poised on a cherry leaf, attentively following the action, and at one point the spotted a suitable hoverfly victim and attempted a capture.
 In the afternoon I came across Ectemnius again. Another female inspecting potential nest holes in a bee hotel, going in and out of them.

 I decided to sit and watch the action, faintly hoping the wasp would start digging a nest. I noticed the characteristic carded silk threads of Amaurobius spiders (top shot), and thought that spiders and digger wasps must come across each other with some frequency as female wasps inspect nesting sites. Then the wasp moved to the log pile under the BBQ and walked in and out amongst the logs. She appeared to have walked onto a silk thread and a false widow spider, Steatoda bipunctata, promptly came out of her refuge. A fight ensued, the wasp trying to bite or sting the spider, the spider spreading silk on the wasp and retreating, and repeating the procedure as the wasp became more and more entangled and buzzed intermitently in her futile attempts to get herself free.

 
The commotion got an Amaurobius out of her retreat, and at some point both spiders were attacking the wasp, although the Steatoda managed to secure it and, when the wasp stopped fighting, the spider cut free the threads that attached the prey to the log, and pull her to the safety of the retreat.

Early stages of the fight

The Amaurobius' legs are visible behind the abdomen of the wasp in the shot above, while the Steatoda secures the jaws of the wasp with more threads of silk

The wasp front end is now tightly wrapped on silk, now the spider focuses on the rear end

The spider drags the wasp to her retreat

 I watched all this with amazement and struggled to get decent photos as the action happened almost behind the log. The whole sequence of events happened within 15 minutes!

Candy-stripe spider

 I found four Candy-stripe spider, Enoplognatha ovata, females guarding their lovely blue egg sacs under the lid of my garden waste bin. The spiders have probably been transferred to the bin with branches cut from some bushes, and had moved with their egg sacs to the drier lid. This one floated down from a thread of silk, and I brought it home to take her portrait on the white bowl. Another thread of silk attached the female to its egg sac, as can be seen on the following side shot:

Although these are small spiders, about half a cm long excluding the legs, they are powerful hunters, and they are able to subdue wasps, honeybees and even the aggressive Wool Carder bees, which they capture on their loose, disorganised web under flowers or leaves, where the females guard their egg sac:

Enoplognatha with its male Wool Carder Bee prey

this one with wasp

with Episyrphus balteatus hoverfly

This one hiding underneath a Feverfew flower got a honeybee

This spider shows a striking color polymorphism, which is genetically determined in a complex way. I have found the three colour forms in my garden. The abdomen can be plain pale yellow (variety lineata, top shot), yellow with two dorsolateral pink stripes (var. redimita):

or yellow with the dorsal surface of the abdomen entirely pink (var. ovata), the rarest in my garden:

In addition to the colour polymorphism the presence and number of black spots is also variable, as it can bee seen in the above photos. This species also occur on both coasts of the USA, presumably introduced from Europe. In the UK, there is a very similar species, also colour polymorphic, E. latimana, which has been recorded mostly in the south of England and it appears to be less common than E. ovata.

Dinner of the green bug muncher

After the very rainy April we are having a teasel growing in the garden is looking very luscious. It has grown a large rosette of leaves, and developed two large leaf-cups which are filled with water to the rim. If you want an account on this fascinating carnivorous plant, check here. I had a peek a couple of days ago to check if any drowned invertebrates were visible. And there were indeed! On the bottom cup (above) a 7 spot floated on a very cloudy liquid, while on the top one, a drowned slug was visible at the bottom of the clearer water, and a few small unidentified insects. What a catch!

Do spiders find ladybirds distasteful?

 I witnessed a curious interaction today. A 7 spot ladybird was walking up a wall, when a sudden movement caught my eye. It was a large spider, a female Amaurobius similis that had dashed out of her burrow in a hole in the wall, probably alerted by the pull of one of the silk threads that radiate from her burrow. She had caught the ladybird by one leg. The ladybird struggled to free itself, but she need not fight much. After a few moments, the spider released her grip, turned round and retreated into her burrow. The spider obviously had assessed the ladybird and regarded it not suitable for a meal. I doubt it was due to the ladybird size or strength, as Amaurobius are powerful spiders, able to subdue large flying insects such as droneflies and honeybees. The other possibility is that the spider has tasted the alkaloid rich liquid that constitutes ladybirds chemical defence mechanism and that is released from their leg joints when alarmed (the 'blood reflex'). I have previously seen dead ladybirds wrapped on silk caught on the webs of two spider species (garden spiders Araneus diadematus and the false widow Steatoda bipunctata). Indeed, field surveys and experiments carried out by John Sloggett showed that A. diadematus does trap and consume ladybirds, and is apparently immune to the toxic effects of ladybird's chemical defences. In contrast, other spider species do seem to find ladybirds distasteful, so this is a strong possibility for Amaurobius.

Another view of the interaction, not as sharp, but it shows clearly how the spider's chelicerae are pulling and lifting the ladybird's front right leg.

For other spiders, however, ladybirds are not even considered a food item. Take this little wolf spider, enjoying the company of the 7 spot ladybird a few days ago. Both individuals were sunbathing next to each other most of the morning. The spider popped in and out, paying no attention whatsoever to the ladybird.

More information

Sloggett, J. (2010). Predation of ladybird beetles by the orb-web spider Araneus diadematus BioControl, 55 (5), 631-638 DOI: 10.1007/s10526-010-9291-0