Thursday, 29 April 2010

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.

Wednesday, 28 April 2010

Ant vs. ladybird

I illustrated in yesterday's post than ants tend scale insects for their honeydew. My orange trees have many scale insects and numerous ants tirelessly tending them. Ladybirds like scale insects too, but for entirely different reasons. Yesterday, I took some photos of a 7-spot ladybird munching on scale insects. Ants, of course, do not like this, and today I managed to witness an ant (or ants) attacking a 7 spot ladybird. The ant was very persistent. It was quite windy, and in several occasions, the ant was blown away only to return to the ladybird a little later. To my eyes, the ladybird defence was passive, she tucked her legs under her body and didn't move much, relying on its shiny and slippery elythra for protection. The ant had her jaws wide open and her abdomen often curved underneath its body, as if it was spraying the ladybird with formic acid. She went for the gap between the thorax and abdomen in several occasions, trying to get a place to bite. After the struggle, the ladybird remained in the tree. There was a Harlequin ladybird on the same tree near some scale insects and I will keep a watchful eye for ant attacks on her too. It was quite challenging to get shots with the wind and the ladybird being in between the foliage, but a series follows.
If you click on this photo you might see the wide open jaws of the ant
Looking for a weak spot
From the back
Curled up abdomen
Looking for the ladybird legs
Harlequin and scale insects

Monday, 26 April 2010

Ants in my plants

The Black garden ant (Lasius niger) is a very successful ant species. Part of their success lays in their adaptability. They are opportunistic in their choice of food: they feed on dead animals, nectar and pollen, seeds and honeydew. They are farmers, tending for aphids and scale insects and collecting the honeydew they secrete in exchange for protecting them from parasites. At the moment, ants are very active, feeding on plum and cherry nectar. They can actually enter the flower where the nectar is hidden. Although ants are known to pollinate a few plants species, they are mostly 'nectar thieves'. The reason the ants do not usually pollinate flowers are twofold. First, they are so small in relation to the size of the flower that they do not seem to touch the anthers or stigmas when entering the flower, and pollen does not adhere well to the ants surface. Second, individual ants  do not travel between different flowers in a single bout of feeding, but just get enough to travel back to the nest from a single flower - notice the distended abdomen of the ants leaving the plum flower on the photo above. They seem to feed on nectar on any cup shaped flowers lacking specific mechanical obstructions to them entering the flower (such as labiatae, the pea family). In fact, aspects of flower shape might be adaptations by plants to exclude these generalistic nectar thieves.
 Black garden ants find Paeony buds secretions irresistible, and it is hard to spot a paeony bud without its handful of feeding ants.
 The ants are now also "milking" scale insects. They encourage the scale insects to excrete the honeydew by 'tickling' them with their antenna.

More information:

C.M. HERRERA, J. HERRERA and X. ESPADALER (1984) Nectar thievery by ants from Southern Spanish insect-pollinated flowers. Insectes Sociaux, 31: 142-154. Here.

Sunday, 25 April 2010

A pair of Hairy-Footed flower bees

On the sides of a little cul-de-sac near University there is a patch of Comfrey. Last year it attracted several species of bumblebees (B. pascuorum, B. pratorum and B. hypnorum) and bees (Anthophora plumipes), which love their dangling flowers. Since the plants started to flower mid April I cannot resist to stop for a few minutes on my way to work. The strategy paid a few days ago, when two A. plumipes were in the patch. The female fed on the flowers while the male went about in his patrolling flight around the clump. Then, the male caught sight of the female and hovered behind her.
A female Anthophora plumipes feeding while a male hovers just behind her.

Now, I must apologize that last year I wrote a post entitled 'Anthophora plumipes: a final post (I promise)'. If you follow this blog you'll realise I have broken the promise several times: I am just unable to stop posting on this little bee.

Saturday, 24 April 2010

Red Mason bee male tactics

I posted about the Red Mason Bees (Osmia rufa) nesting in our bee post last year. The males  have now been active for a few weeks, and they are quite interesting to watch, as they are very inquisitive and interactive with other insects. The different behaviours of male bees depend to some extent on how the resources used by females - such as nesting sites and food plants - are distributed. These resources indicate where females are to be found, and to maximise their reproduction males are to encounter and mate with as many recently emerged females as possible. In Osmia rufa, females are thought to mate only once shortly after emerging from their nest, as males guard females after mating and impregnate them with chemicals that make the females unattractive to other males, effectively ensuring their paternity. As many other bee species, Red Mason Bees are polylectic - they are quite generalistic as to what flower species they feed on - and their nests are quite scattered (at least in natural habitats!), and therefore it does not pay to be territorial. In a 1988 paper I read today, Karsten Seidelmann graphically described Red Mason Bee behaviour based on 364 individually marked males:

In order to find mates, each male roamed about his home range. These home ranges were located around flowering groups of foods plants, but also by nesting places. Occasionally sunny places (exposed leaves, stones, etc.) or bushes of dwarf pine in the surrounding of large nest aggregations were inspected and patrolled as well. Home ranges sometimes also consisted of several small patchy encounter sites. Males then searched within the patches and flew in a straight line between them. Every home range contained an exposed sunny place where the resident male basked between patrol flights at irregular intervals. When home ranges become shadowed, males turned to other areas, returning when the area was in the sun again. Areas abandoned because of shadows were not occupied by other males.

The photo heading this post shows a male next to a potential nesting hole in our bee post. The males often enter and inspect the holes and look out.
These little bees often chase and make contact with other bees - not only of their own species but also other insects such as butterflies in their home range - and I had misinterpreted this behaviour as agressive, an indication of territorial behaviour. Seidelman's detailed observations, on the contrary, shows that the Red Mason Bee is not territorial. It does have a 'home range' but these are not exclusive to one individual and home ranges of different males partially or totally overlap. Males also occasionally went on 'excursions' away of their home range. Their chasing and making contact with other visually detected insects is an 'inspection' behaviour: they check if they are conspecific females or not, but they do not attempt to drive them away:

Home ranges ranged from 3 to 30 m2 in size. Males continuously altered their home ranges in response to changes in possible encounter sites. Plants that started to flower were integrated in adjacent home ranges, or new home ranges were established and old ones were abandoned. If females emerged from a large aggregation of nests, the searching activities of several males were concentrated entirely on these nesting places, with males inspecting nest entrances frequently.
Males inspected all resting and flying insects with an O. rufa-like shape during their patrol flights. They approached other solitary bees (e.g., Osmia, Megachile, Anthophora, Andrena), as well as honeybees (Apis), bumblebees (Bombus), or even flies (e.g., Calliphora). However, only receptive females of their own species were mounted, whereas males of O. rufa and other insects were abandoned immediately after a short contact.

Seidelman also analysed the reproductive success of males, that is, how many times they mated throughout their lives and concluded that this is independent of the male body size.

More information at:
Karsten Seidelmann (1999) The Race for Females: The Mating System of the Red Mason Bee, Osmia rufa (L.) (Hymenoptera: Megachilidae). Journal of Insect Behavior, Vol. 12:13-25. here.

Robert John Paxton (2005) Male mating behaviour and mating systems of bees: an overview. Apidologie 36:145–156.

Tuesday, 20 April 2010

Snail season starts

After a few dry sunny days, rain fell non-stop yesterday. A few Garden snails (Cornu aspersum = Helix aspersa) had woken up from their winter rest and were slithering around the garden. The start of snail season.

Monday, 19 April 2010

Night prowl

I had to go out late at night in the garden a few days ago. I took the torch as I dislike squishing slugs or snails walking on the path. Indeed, there were a few yellow slugs (Limax flavus), garden slugs (Arion hortensis) and Common rough woodlice, but, surprisingly, prowling in the middle of the path, I found a shockingly bright-coloured female woodlouse hunting spider (Dysdera crocata) - of which I wrote a post recently.
The spider seemed uninterested in woodlice, by the way, as it walked around one of them. A pleasure to observe this nocturnal spider in its environment.

Saturday, 17 April 2010

Making cherries

We've got a small cherry tree in our garden. In addition to making a spectacular show when it blooms, it produces the sweetest cherries and, although the crop can be a bit hit and miss depending on the spring weather, it is a bug magnet for a few months. The tree only started flowering a week ago but today was buzzing with bees. I spent some time this morning watching the blossom and trying to ID the bees that are feeding on it or visiting. Anthophora plumipes and Osmia rufa males have incorporated the tree into their patrolling routine, circling around the blooms, chasing other bees and keeping track of the females. Beautiful, velvety shiny red female Andrena fulva were also feeding on it as were female A. plumipes. I stopped counting the honeybees as there were quite a few. To the high pitched buzz of the Anthophora bees, the deep buzz of queen Bombus lapidarius and Bombus terrestris was added. These busy lot of creatures were involved, without realising it, in fertilising the blossom and contribute to making the cherries that hopefully we'll eat this summer.
Peacock butterfly
Bombus lapidarius
A full Andrena fulva sunbathing near the tree.
Outside the blooming season, which lasts a few weeks from April to May, the tree growing buds are covered on black aphids that in june produce a sweet sap, loved by bumblebees, especially Bombus terrestris and Bombus hypnorum. I have also seen Bombus pratorum feeding on the nectaries at the end of the leave stalks. Aphids also attract scores of ladybirds. The cherries themselves are prized by wasps - and birds.

Sunday, 11 April 2010

The soil dwelling 'eightypedes'

When collecting some compost that had formed on the concrete under a large vine, I came across half a dozen subterranean centipedes. Despite having no eyes, they appear annoyed when exposed and try and hide under the soil as fast as they can, with their antenna moving very fast feeling the way. They are slower than the Lithobius, but their long snake-like bodies makes it quite tricky to get good shots, so I was quite pleased with the one above. This is Stigmatogaster subterranea (previously known as Haplophilus subterraneus), which usually has between 77 and 83 pairs of legs. I counted about 80 on a photo, a bit short of a hundred to deserve the name 'centipede' - which anyway, no centipede has, as they always have an odd number of pairs of legs - but still a respectable number. This species is blamed for nibbling roots of crops, and it feeds on vegetal and animal matter, but last year I witnessed a titanic struggle of a grub of some sort with an specimen of this centipede just at ground level. You would wonder how on earth did I happen to notice this, and the reason is that I had just seen a queen bumblebee digging into the soil and I wondered if she was going to make a nest and waited patiently watching until the two struggling pair of bugs nearby on the ground catched my attention. The fight carried on for some time but, unfortunately, I do not know how it ended. It just seemed too large a prey for the centipede. The grub moved its body around and the centipede curled around it, and, as you can see in the photos, tried to bite with its fangs. From the photo it appears that either the skin of the grub was too tough or the bite too wide for the fangs to pierce it - and therefore to inject the venom. In any case, it is quite unusual to come across some subterranean bug actually behaving, as opposed to simply disturbing it.
The centipede curling around its catch.
In this photo you can see the darker fangs opened under the centipede head, trying to pierce the grub.
Another shot with fangs.

The common woodlouse

With this photo of a Common Woodlouse (also known as shiny or smooth woodlouse) Oniscus asellus, let me round up the topic of woodlice. Woodlice are crustaceans, a mostly marine group. They have 7 pairs of legs when adults. They are quite gregarious, and usually many individuals are found together. The common woodlouse is not as drought resistant as the rough woodlouse, as their bodies are more permeable to water, and therefore is present in more humid microhabitats. It has a very shiny cuticle with dark and light patches, although colour varies, their antenna are longer than in the rough woodlouse. We found these large individuals (this is the largest UK species and can reach 16 mm in length) today under large logs kept covered with some tiles.
A side view of a different individual.
A front view of the first individual.

Saturday, 10 April 2010

Grape Hyacinth visitors

Many nectar-feeding insects prefer to use abundant floral resources. That is, a plant is much more frequently visited when there is a large clump of the species together or it flowers profusely, just because the insect has to travel less to obtain the same amount of energy. I have experienced this first hand in my garden with Grape Hyacinth (Muscari armeniacum) an early flowering bulb with clusters of deep blue flowers at the top of a spike. This year I have several large drifts of this species, which has been flowering for the last month or so and this has been rewarded by an unusually high diversity in the species visiting the flowers. Here is a selection of photos taken in the last few days on this plant.
Anthophora plumipes female loaded with yellow pollen and feeding on the flowers
Anthophora plumipes male, leaving the flowers with his tongue still extended
A male Red Mason Bee (Osmia rufa) sunbathing on a stone next to a Muscari clump. The first males of the year appeared today and I have watched them feeding and patrolling the plants, making sure they weren't missing any of the females. The males kept checking the Anthophoras.
A Peacock visiting the flowers. Grape hyacinths are also visited by Commas and Small Tortoiseshells (see here for photos)
This scruffy-looking dark bee with white tufts of hair is Melecta albifrons, the cleptoparasite bee (cuckoo bee) of Anthophora plumipes.
I have got no photos but a couple of days ago I saw an Andrena fulva and a queen Bombus pascuorum (both first of the year) visiting Muscari in my garden.
UPDATE 11/04/10
Today a queen Bombus terrestris visited the Muscari patch and I managed to get a shot of the first Osmia rufa of the year feeding on it as well.

UPDATE 17/04/10
A Green-Veined butterfly fed on the Muscari patch.

Friday, 9 April 2010

The common rough woodlouse

Although woodlice have been mentioned in BugBlog a few times, they haven't been the main character in any post yet, and this has to be addressed. This little group I found yesterday under a pot gives me the perfect excuse. There are over 3,000 described species of terrestrial isopods (woodlice) in the world, with only 35 native to the UK. The Common Rough Woodlouse (Porcellio scaber) - above- is one of the most common. Unlike the Pill Woodlouse (Armadilium), it is unable to roll into a ball, and instead, its defence mechanism consists in grasping the substrate and pressing its dorsal armour against it, so that its more vulnerable underside is protected. Its nocturnal habits and love of humid places reflect the fact that it loses water very easily from its body due to transpiration as their surfaces are not waterproof. Woodlice absorb water from their surroundings when they rest under stones, in compost heaps or similar places and they lose it when they forage away from their refuge. They are detritivores and feed on dead vegetable matter and therefore are involved in the decomposition of dead leaves and the production of compost.
 Woodlice usually have separate sexes, that is, there are males and females. Females brood the eggs and their young in their first instar, suplying them with nutrients and water, in a pouch under their body. In the common rough woodlouse, females can produce three broods (of around 20 young) a year in good conditions. Breeding is very seasonal, and starts when days become longer (16 h light). Woodlice can live several years.

More on little pole vaulters

After researching and writing my first post on springtails, I suddenly have become much more aware of these tiny bugs. Yesterday in the garden, I came across quite a few. Something I didn't mention is that springtails can be very colourful. Once I cropped some of my pictures - I am working on the edge of the resolution on my Powershot G10 camera - the patterns on the abdomen of this tiny, oddly shaped, and appropriately named Dicyrtomina ornata appeared as quite striking. Found when lifting the plastic lid of a sandpit.
I also came across a relative of the maned species I found in the conservatory; although hairy, this one has clear bands in the abdomen, and also banded antennae. I think it is Orchesella cincta.
The sand grains gives an idea of scale. 
Some springtails had fallen on a little puddle and died. This one shows the little 'pole' they use for jumping extended behind its abdomen. Normally, the mechanism is tucked under their body. I made one springtail jump just to see the level of control they have on where they land and the direction. They seem to jump 'forward' most of the time, but the length of the jumps varied quite a lot.
Finally, this is the tiniest springtail I've seen. Less than 2 mm in length, maybe just 1 mm. I do not know what species it is. I found it under a bonsai pot.

More information
This page has identification and distribution information on UK springtails.

Wednesday, 7 April 2010

The log pile revisited

We made a couple of log piles in the garden last year. Today I dismantled one of them to check what was in it. This was a very 'untidy', and relatively dry log pile, with the logs having been covered on branches from pruning bushes around the garden and the location being under a large Philadelphus bush. The first finding was that a lovely crumbly pile of compost had accumulated around the logs. There was a lot of bug activity in the pile. The most abundant form of -visible- life were woodlice, especially the common rough woodlouse, Porcellio scaber, which made the compost move as they were so many, also some smooth woodlouse, Oniscus asellus and common striped woodlice Philoscia muscorum. I found three species of snails: many common garden snails, Helix aspersa (=Cornu aspersum) most of them hibernating; a yellow banded snail Cepaea (one of 5 specimens we released in the garden a couple of years ago), and several Glass Snails Oxychilus draparnaldi (photo above). Several yellow slugs Limax flavus crawled around. There were quite a few spiders, amongst then a very large Tegenaria and possibly an Amaurobius, which rapidly disappeared amongst the logs. I also found some Blunt-tailed Snake Millipede (Cylindroiulus punctatus), which coiled into a spiral when disturbed. I saw some new springtails, but I couldn't get a decent photo. As for insects, a Harlequin seemed to be hibernating on a log. By far the most shocking thing was a couple of enormous earthworms, Lumbricus terrestris, which I found while they abandoned the log pile - possibly feeling the disturbance - by creeping on the ground. One of them was so large that at first I thought it was a snake! Big fun examining this log pile, I am sure I forgot to mention some bugs. I didn't even go through the whole of it but it yielded quite a number of interesting finds.
A banded snail, some woodlice and an earthworm
Garden Snails
Three species of woodlouse can be seen in the image
A specimen of the millipede Cilindroiulus punctatus
The largest earthworm I've seen in my garden, creeping on the ground
The same earthworm being held, just for scale
A yellow slug, Limax flavus