The nest robber

I was puzzled when I checked the bee hotel a couple of days ago. The painstaklingly, lovingly filled nesting cells of the Osmia leaiana nest that illustrated a post a few days ago were gone. There was pollen everwhere and the nest walls made of chewed leaves weren't there. A Megachile willughbiella female, a leafcutter bee, was inside, rubbing its scopa against the walls. Was she the reason for the disappearance of the smaller mason bee's nest or just taking advantage of a previous nest predator?
 Although I'll never know for sure, I think that the leafcutter is probably to blame. There are plenty of empty cavities in the bee hotel, but she apparently decided that this was a better hole than the rest and probably fought the mason bee out of her nest (Leafcutters have formidable scissor-like jaws, and this leafcutter species is a large bee), and then proceeded to empty the contents, eggs, pollen, nectar and walls to make space for her cells. Today, the leafcutter had completed her first cell (above). Note that the walls are still covered in yellow pollen.
 The bee nestbox is providing plenty of surprises and allowing observations very difficult to make in natural holes. The events illustrated here remind me that competition is fierce out there, although in the case of hole nesting bees, it will pass unnoticed in the darkness. Many bumblebee queens are ousted from their nests by other bumblebee queens, not necessarily from cleptoparasitic species, which take over after a fight. In solitary bees and wasps, suitable nest holes might be limiting and intra and intraspeficic competition might be rife, although fights may often take place inside holes. Watch this fascinating video of three bees fighting for a nest hole by George Pilkington, and this series of photos by Simon Saxton documenting two Ectemnius wasps fighting for a nest hole. Nest lining thicker end walls provides physical defence, and might not only protect against cleptoparasitism, but also against other bees taking over, stealing the nest hole and destroying the nest contents.

7th of July. A female Osmia leaiana working on her nest. Note the remains of last year's leafcutters nest in the cavity under it.

16th July, a female leafcutter emptying nest contents by scooping pollen.

Mouse spider nest

As I checked the bee hotel, the Mouse Spider, Scotophaeus blackwalli, was looking considerably thinner than last time I checked. And lo and behold! She was guarding a fresh, pure white silky cocoon holding her eggs in a neat bundle. I will update this posts with further developments.

UPDATE 9th July. The female is still sitting right on top of the egg sac.

Spider eggs and egg sacs

Spiders make remarkable mothers. One of the most widespread maternal behaviours is the more or less elaborate construction of an egg sac, and many species are making them at this time of the year. The mother wraps a batch of eggs - which might be the only one she will produce during her lifetime - into a neat parcel kept together with silk. The egg sac can protect the eggs from parasitic wasps, or from predation - sometimes from other spiders. In addition, egg sacs are often guarded by the mother, like the Neriene montana above (28/05/2014) or Garden spiders (below), Araneus diadematus, which guard their large egg sacs until they die at the end of autumn (30/10/2011).

Holding the egg sac is another maternal behaviour. An example is Pholcus phalangioides, the splindly daddy long-leg spider. She makes a simple egg sac, with the eggs clearly visible through the lax packaging. She keeps the eggs on her mouthparts until the spiderlings hatch (22/07/2009).

Being mobile spiders, wolf spiders and nursery web spiders actually carry their egg sac with them wherever they go. This allows the eggs to develop faster, as they warm up when spiders bask in the sun.

Wolf spider, Pardosa sp. carrying her egg sac (31/05/2011), attached to her abdomen.

Nursery web spider carrying its large egg sac (19/06/2011).

In the family Gnaphosidae, the female not only guards the eggs, but she makes her egg sac inside a folded up leaf, locking herself inside with the eggs (19/07/2010):

But egg sacs are often found alone. Some of them have a stalk, like those of the genus Ero, also distinctive by their covering of coarse red silk (7/04/2013):

Others are truly unique, and is the best way to identify the species, like the sputnik-like egg sac of Paidiscura pallens, a tiny spider (28/05/2014).

Eggs vary in colour, I love the soft pink eggs of Steatoda bipunctata (28/05/2014)...

 ...and also the baby blue silk of Enoplognatha sp., revealed here while picking apples (30/08/2011):

These are just a few examples, from common spiders you can find in your own garden, which illustrate some of the diversity of spiders.

New guest in the bee hotel

As I removed one of the sides of the bee hotel to examine the progress of the Red Mason Bee nests I found that one of the cells had been occupied by a mature Mouse Spider female, Scotophaeus blackwalli, in her silk cell, looking like she will be ready to nest soon. Although she retreated to the bottom of the groove, she was still there the following day.
These spiders wrap their eggs in round white silk sacs under bark or in crevices in and around houses, and the female sits by the nest, guarding it. These spider nests are not easy to observe without disturbance, as they may fall apart as they are uncovered, or the female might flee. I am therefore quite pleased with this new guest, as, if she decides to stay, I should be able to watch her nest with little disturbance.

More information on the family Gnaphosidae here.

Red Ant nest

We found this Red Ant, Myrmica sp., nest under a stone. The chamber in the middle of the photo had many workers tending larvae, and what appeared to be a queen, a bit larger with darker head on the top left corner. With the ants, there were a few Cyphoderus albinus, a species of white springtail which is often found inside ants nests. There were also many millipedes, thread-like, blind, with red spots, Blaniulus guttulatus.

Blaniulus guttulatus millipede

White springtails, millipedes, red ands and a slug

Chewing me timbers!

From June to October, I find Ectemnius digger wasps in the garden. They are formidable hoverfly hunters and, close up, they look so fierce: all enormous, forward facing eyes and long, sharp jaws. Females bore nests in soft, dead wood using their jaws: a central burrow with lateral cells which they stock with flies. They will lay eggs on the flies and leave their nests for their larvae to feed on the flies when they hatch. They use dead branches on trees, laying wood and even visit bee hotels. Males are often found inspecting holes in dead wood, in search of emerging females.

Year after year, these wasps come back to my log pile under the barbecue. A few days back, I watched a female searching for suitable nest sites amongst the logs. She settled at the end of a lime log and started chewing the wood, producing abundant sawdust in the process (top photo). She carried on for a while, although at the end I think she settled for a different log, as today a large pile of sawdust had accumulated underneath (below).

For more posts on Ectemnius digger wasps click here.

Tawny mining bee nesting aggregations

I have been posting on the Tawny Mining Bees, Andrena fulva, recently. I have been watching suitable nesting sites for signs of activity and today I came across many nests located in groups in several grassy areas. It was a bit windy and the female bees often missed their nests when landing. Instead of walking the short distance, they would fly again, carry out what looked like a positioning flight, and landed on top of their nest mound and got inside.

 Some females seemed to be looking for good places to nest, and tentatively would start digging in the soil amongst other nests.

Males were patrolling around, jumping on passing females. Tawny Mining Bees, like many other bees and wasps, tend to nest in clusters, many nests will be located near each other, when apparently suitable habitat is plentiful around them. They like areas of short grass and the fresh pellets of soil soon stick out like mini mole hills on lawns, verges and park greens.
 Why do bees nest in this way? They are solitary, so each bee will make her own cells and storage pollen and nectar toward her eggs. Apparently bees are able to detect the smell of conspecific active nests and preferable fly towards them; they also tend to return to their natal sites, and, obviously, successful nesting areas would tend to increase their nest density with time. These are proximate explanations, they tell us how bees actually find the nesting sites. But do bees actually benefit from nesting in an aggregation as opposed to doing it on their own? Aggregated nests must have a strong benefit to counteract the costs associated to the behaviour, such as increased competition or higher diseased transmission. Five hypothesis as to the adaptive value of nesting aggregations have been put forward:
1) Bees might be selecting very specific environmental conditions to locate their nests, for example, soil of a particular consistency or nectar sources nearby. This hypothesis has been investigated and appears to hold for some species, but not for others.
2) Nest sites might act as "information centres", where bees would find from others where the best foraging resources where. This, although possible, has no empirical support.
3) Newly nesting individuals might nest in aggregations because they act as markers of successful nesting sites.
4) Bees might benefit from reusing old nests, so that some of the costs of digging would be offset.
5) Nesting communally might offer some antipredator or antiparasite benefits, maybe by confusing predators, or communal defence. Data in support of this hypothesis is conflicting: parasites can either favour aggregations, by being more effective the less aggregated bees are, or dispersed nesting, when they locate clumped nests more effectively. Some bees gain protection from parasites by nesting communally, for example, as I covered in the recent post on Melecta, individuals of the host species Anthophora attack parasites near their nest, therefore conferring some protection to neighbouring nests.
Whatever the reasons, Andrena fulva nesting aggregations must be one of the easiest to observe in British solitary bees. Just look for their little molehills on the grass. A little red head might be peeking from inside.

References
Michener, Charles D. (1974). The social behavior of the bees: a comparative study. Harvard University Press. Other: ISBN-13: 978-0674811751

Rosenheim, Jay A. (1990). Density dependent parasitism and evolution of aggregated nesting in the solitary Hymenoptera Annals of the Entomological Society of America, 83 (3), 277-286

More on maternal spiders

I posted recently on maternal behaviour in spiders, but I when I came across this I knew another post was in order. The photo above shows what is is most likely a Gnaphosidae spider with her eggs in her nest on the 19th of July. The spider has wrapped herself inside a silken nest she has made for her eggs, and she will remain there until they hatch and the spiderlings disperse. This behaviour, called 'egg guarding' is present in many spiders. Why would a spider do this? Do the eggs benefit in a any way from their mothers behaviour? There is anecdotal evidence in related species that unattended eggs are predated, but little information was available on who the predators are until Simon Pollard carried out some experiments on Clubiona cambridgei, an endemic species from New Zealand displaying this egg guarding behaviour, and the results were surprising.
 Simon had noticed that sometimes Clubiona spiders were found inside or just outside nests with eaten eggs and suspected that individuals from the same species were actually the egg predators. Egg predation seems an unusual behaviour for spiders, who are considered hunters of active organisms. He wanted to test the hypotheses that (1) spiders eat eggs from their own species - a form of cannibalism - and (2) egg guarding represents a defensive mechanism that decreases the chances of conspecific predation. He carried out simple experiments with egg nests - easily collected in this species as it is abundant and nests in folded out flax leaves. His results were conclusive. Nests where mothers had been carefully removed (therefore, unattended) and then were exposed to non-breeding females were all predated, with all eggs eaten within 16 h. Males or breeding females did not eat unatended eggs. When nests were attended, males and non-breeding females quickly retreated when noticing the activity of the guarding mother and no egg predation took place.
 Therefore egg guarding in Clubiona is indeed a strategy to protect the eggs from other spiders predation. More recently, cannibalistic egg predation has been documented in 12 spider families - including Gnaphosidae -, and therefore, egg guarding behaviour is likely to have the same defensive function in these spiders against cannibalistic predation.
My spider successfully defended her eggs, and yesterday, I could see the pale, tiny spiderlings through the nest walls.

More information
Pollard, S.D. (1984). Egg guarding by Clubiona cambridgei (Araneae, Clubionidae) against conspecific predators Journal of Arachnology, 11, 323-326
Nyffeler, M., Breene, R., Dean, D., & Sterling, W. (1990). Spiders as predators of arthropod eggs Journal of Applied Entomology, 109 (1-5), 490-501 DOI: 10.1111/j.1439-0418.1990.tb00080.x

Queen Common Wasp

Queen common wasps (Vespula vulgaris) have been around for a few weeks now. I never see them feeding, just sunbathing, flying about the apple or cherry, but not appearing interested in the flowers, or searching for a suitable nest site. Today this one found our hedgehog house (hedgehogs, still snubbing this lovely house, better hurry up before wasps finish it off). The wasp started chewing at the old wood. Wasps make their nests out of saliva mixed with chewed pulp, which becomes pretty much paper mache and this queen is now building up hers.

Wasp nest

Wasps nests have been described as 'human head' shape and size and it's not far from the truth. I photographed this old abandoned nest in November, under the eaves of an Edwardian house. I bet that the owners couldn't open the windows in the summer without getting a stream of wasps in! All the wasps from this nest, except the new queens, are now dead. The queens will hibernate and come out in March, where there are often seen sunbathing, to start new nests. Most of the wasps we see in the summer are worker wasps.

Bumblebee home ranges

Have you ever wondered where do the bumblebees visiting your garden come from? How far do they travel from their nests? How can scientists find this out? It would appear that an obvious strategy would be to mark bumblebee workers from single nests, survey the surroundings of the nest and map where they go. In practice, this proves difficult as it is difficult to find enough marked workers in a reasonable amount of observation time. Another option is to mark bumblebees, release them at increasing distances from their nests and see how well they return home. When this last experiment was performed bumblebees -Bombus terrestris in particular - could return home from the astonishing distance of 9.8 km! However, this does not show how far from their nest they normally forage. In this paper, Mairi Knight and co-workers used an elegant, sophisticated, but cost-effective approach which yielded a lot of data. The premise of their work is that the workers from a nest are expected to be full or half sisters - offspring of the same queen. What they did is to follow a linear transect capturing workers of four common bumblebee species at regular intervals.

The sampling design: across agricultural land, with some woods, hedgerows, and a nearby town in Hertfordshire. The sampling points (in red) are approximately 250 m apart.

They screened the workers using 8 to 9 very variable genetic markers (microsatellites, which are also used in human paternity testing) and identified sisters by assessing the number of markers sisters should be expected to share. Their results were then used to calculate the maximum foraging distances of nestmates of the four species. It was 449 m for B. pascuorum, 758 m for B. terrestris, 450 m for B. lapidarius and 674 m for B. pratorum. Quite a long way, I would say. B. terrestris is the species flying longer to forage, and also the species with the larger workers and more workers per nest. A much more striking result of this study, though, is the number of nests from which workers come to feed in a specific sampling point. Knight and coworkers estimated that, on average, B. lapidarius workers came from 75 different nests to a specific sampling point, these figures were 43 nests for B. pascuorum, 52 for B. terrestris and 37 for B. pratorum. Of course this study applies to farmland, but for B. terrestris, nest densities might be even higher in urban areas. It makes me feel good to know that even when, frustratingly, there are no bumblebee nests in my garden, it still supports a very high number of nests from a range of species.

The hoverfly hunting machine: watch digger wasps from your garden bench

In 2003, quite a warm summer, an interesting wasp kept watch of the cloud of hoverflies (mainly Episyrphus balteatus) on the nearby flowering Hebe bush from my garden bench. It was there every day and I called it 'Benchy'. A browse in the Chinery guide - the 'Bible' for insects in the UK - showed it was a wasp of the family Sphecidae - a digger wasp. Digger wasps are hunters specialising on various insects, which they paralise and stock on nests to feed their larvae. They excavate their nests, often on the ground, and thats why they are called digger wasps. Wild About Britain provided the ID for the genus, Ectemnius, and even a few guesses for the species ID: E. cavifrons, E. cephalotes and E. sexcinctus, with the first two being the most common. The wasp has returned year after year and I have managed to assemble a collection of photos illustrating a few aspects of the natural history of this fascinating animal.The wasp is yellow and black, with a big head and very large eyes, which make a large area of the head - a very different feel from a common wasp. It is indeed a highly visual animal and it nervously scans around in search for its favourite prey. Oher species of the genus like to hunt other types of flies but Ectemnius cavifrons favours hoverflies.

 When a potential prey is detected, the wasp hovers like its prey, staying stationary at around 10-20 cm from the fly. You need to be quick to manage to focus it, as the wasp is wary of anything large approaching it. The prey is then attacked swiftly, and if the capture is successful, the fly is taken to the nest.

I managed to shoot a hovering Ectemnius wasp, unfortunately a blue plastic car ended up being the background, doh!
For a few years 'the nest' seemed to be located far away from my garden as the wasp disappeared into the distance carrying its booty. But last summer I got lucky and I managed to locate a nest in a dry log in the pile of wood under the BBQ.

Ectemnius wasp about to leave its nest hole.