Sunday, 3 July 2016

Sputnik spider and egg sacs

Yesterday evening, while pruning the plum tree, I found the distinctive egg sacs of the theridid Paidiscura pallens: they are white with pointy projections that make them look like the Sputnik satellite. The tiny mother, less than 2 mm in length, sat atop hers oversized egg sac, which was attached to the underside of the leaf and to the spiders loose, tangled mess of silk threads. She nervously moved back and forth from the sac and around it, like sensing that something was amiss. Despite finding the egg sacs regularly, this is the first time I see the female spider guarding it. I found another pair of egg sacs today under a plum leaf, also guarded by the mother.
Two Paidiscura pallens egg sacs also from today. 
The female and her two egg sacs from today.

Wednesday, 29 June 2016

Bees toiling for nectar

Many flowers, closely protect their nectar in deep nectaries (e.g. the Mint family) or behind barriers made by modified petals, like pea flowers. This way, unspecialised nectar feeders, which may not be good pollinators such as ants might not be able to access the nectar, but bees, which will visit many flowers in succession and are effective pollinators will be able to. These modified flowers have their pollen-bearing anthers on the roof of the modified petal blocking the entrance. The bee, while coming in to feed on the nectar, rubs its back on the pollen, ensuring she will pollinate the next flower she visits. Bees, however, often have to work really hard to get at the nectar.
 A few days ago I watched a common carder bee, Bombus pascuorum, feeding on Iris flowers (top photo). It tried to get in through the side unsuccessfully, but eventually found the way in pushing through the middle of the landing petal (which are called 'falls').
Later, a female Osmia caerulescens, landed on a Phlomis flower, she seemed to sense there was nectar behind the hooded petal closing the flower and pushed with her head until it managed to get under it. It spend quite a long time inside, I guess this is a nectar-rich plant and it will take a while to empty the nectaries for a small bee like this.
Osmia caerulescens getting in.
The bee just before leaving the flower after feeding.

Saturday, 25 June 2016

Stretch spider portrait

I found this female stretch spider, Tetragnatha, in the garden this evening. I remembered that they have lovely faces and I gave it a try on the white bowl aiming for a frontal shot. They have their eyes in two rows, the bottom central pair facing forward. The face shot also allows to see its enormous fangs. After a short session in the bowl, I returned the spider to her leaf and she rapidly climbed to her retreat.
The resting position of Tetragnatha on a leaf.

Friday, 24 June 2016

Lekking long-horn moths

 In a walk by a wooded area on my way to work yesterday, I came across a few small swarms of dancing long-horn moths. I watched and waited until one of them sat to rest on the foliage: a Yellow-barred Long-horn moth, Nemophora degeerella. Long-horn moths are truly spectacular micromoths. Males are not only beautifully marked with metallic golden, chestnut and blue metallic stripes and a broad diagnostic yellow band across the wings, but their antennae are extremely long, several times their body length. It is astounding they can actually fly! Not only they can fly, but they perform a dancing flight, males bobbing up and down in a small area in shady wooded glades where they gather forming mating swarms or leks. These swarms, and possibly pheromones the males emit presumably serve to attract females and mate. Do females prefer males with longer antennae? These are day flying moths and I've watched the swarms in the morning or afternoon in warm sunny days in May and June. The antennae are white and so stand out as the moths fly. Although I've never seen a female, they are similar to males, but with short antennae. The caterpillars feed on leaf litter.
 This is a short video of one of the moths appearing to sip honeydew from a leaf.


UPDATE 28/06/2017
A large swarm (over 20 moths) in the University Woodland area


via GIPHY

Monday, 6 June 2016

Why do male Wool-carder bees defend a flower patch?

I found the first male Wool Carder Bee, Anthidium manicatum of the year in the garden today, patrolling and basking on the large sage patch that is a favourite if many species of bee. If you have a flower-rich garden with a sunny aspect, chances are that in warm, sunny summer days you will see this chunky bee attacking other flower visitors, including large bumblebees. Male bees from most bee species often just hang around nests where they can mate as females emerge, or patrol flowers favoured by females. Occasionally they 'jump' onto or chase other bees or insects, possibly checking if they are females. For example, Male Hairy-footed flower bees, Anthophora plumipes, who emerge a week or so before females, will jump onto bluebottles, the only insect that roughly resemble the black females of his species. No other male bee is as aggressive actively defending a patch of flowers as Wool carder bees. They even have sharp spines at the end of their abdomen with they can use to harm, or even kill, other bees, so they rapidly become the only bees using the flowers
The abdominal spines of male Wool carder bees

 Most female bees mate once shortly after emergence, so males only had a chance of mating successfully early in the season. Females store the sperm of this early mating and use it to fertilise their eggs throughout the nesting season. Females will repel or avoid courting males vigorously once they've been mated. In contrast, Wool-carder bees are unusual in that females both mate multiple times and accept matings throughout their flight season. Witnessing solitary bees mating is quite rare, but with Wool carder bees, matings are quite frequent. Many females visiting a defended flower patch will mate with the resident male. The male defending a good flower patch will likely gain many matings with several visiting females, but, given what we know about sperm usage in solitary bees, will he benefit from fathering the female's offspring?
Mating Wool carder bees

 In a recent study, Kathrin Lampert and colleagues from Ruhr-University Bochum carried out some experiments to investigate why Wool Carder bee mating behaviour is so different from other bees. They in particular were interested in testing the hypothesis that Wool-carder bees might show what is known as 'late male sperm preference' in which the last male mating with a female has a disproportionally higher chance of fathering the females offspring.
 To find out 'who is the daddy' they used genetic testing in a similar way to how paternity is tested in humans, using genetic markers that have many variants, and therefore are likely to be different between individuals. In order to be able to capture the likely mothers and fathers of particular nests they constructed large flight cages containing Betony plants (for pollen and nectar) and Stachys byzantina (for plant wool, which the females collect to line their nest cells). Wool carder bees nest readily in sections of bamboo sticks, and they fixed artificial nesting sites inside the flight cages. Offspring of a female are found in a linear nest in consecutive order, the deeper cells in the bamboo stick contain the earlier laid eggs, while the cells closer to the entrance contain the later brood, which is likely to be male offspring. They carried out three experiments, in the first one, to test the feasibility of these experiments wild males and females (likely to have mated before) were captured, individually labelled with a dot of paint in the thorax, and released in the flight cage. In the second experiment, males in the cage were swapped to test if males with later access to females would father offspring. In the third experiment males were removed after a few days and females left to nest with no males, to investigate if females are able to store sperm. After the females had completed their nests in all the experiments, DNA samples were taken from the males and females, and them and the offspring found in the artificial nests screened for genetic paternity analyses.
A problem with their experiment were cleptoparasitic wasps, which destroyed the bee larvae and prevented genotyping. Another problem, which stems from bee's sex determination system, is that only female offspring have a dad: males develop from unfertilised eggs, so they only have a mum. They could only find out if offspring were male or female after genetic screening. Despite this, they obtained a number of female offspring from many females.
 The results revealed that the males flying with females at the time the females were provisioning a cell, where they are close to laying the egg, were the most likely fathers of the offspring (84% of the time), whereas most of the remaining fathers were males present in the cage in previous days, supporting the hypothesis of late male sperm preference. Males that were dominant, that is, chased away other males from flowers, tended to father more offspring, as most matings happened on flowers.
 The male removal experiment showed that females were able to store sperm for at least 11 days, and possibly much longer.
 This research suggests that a predisposition for late male sperm precedence in the ancestors of wool carder bees might have been what favoured the aggressive territorial behaviour seen in males, as they can benefit from monopolising floral resources visited by females.

More information
Lampert, K. P., Pasternak, V., Brand, P., Tollrian, R., Leese, F., & Eltz, T. (2014). ‘Late’male sperm precedence in polyandrous wool-carder bees and the evolution of male resource defence in Hymenoptera. Animal Behaviour, 90, 211-217.