Wednesday, 27 July 2011

Bright brimstone

The sun came out in the afternoon after a grey start, so I went again to my local wildlife garden for a Big Butterfly Count. Although I was disappointed not to see Ringlets or Gatekeepers, the fact that I found the Brown Argus again - this time two individuals - and this fresh male Brimstone made up for it big time. Brimstones, Gonepteryx rhamni, are beautiful, but frustrating butterflies. In the last three years I've seen 13 individuals, and until today, I had only managed to get very distant shots of two of them, the rest flew and flew non stop. The Brimstone hibernates as an adult and is a long lived butterfly. The adults emerge at the end of July or early August, and they can live up to 10 months. Compared this with the few weeks (4 days on average) that Brown Argus can live.
 This male Brimstone fed on Hemp Agrimony for quite a while, and then moved on to buddleias. It was so content feeding that I could get very close for shots. Brimstones have long tongues and they can feed even on Teasels, which have very deep corolas. While in flight, the Brimstone is very visible, but once it lands, its yellow-green colour and the asymmetric dots on its wings give it has a fantastic camouflage, appearing to be a droopy, yellowing leaf.
The Big Butterfly Count. There is time until the 7th of August if you haven't done one. You only need 15 minutes in a sunny spell.

The little Brown Argus complex tale of range expansion

Climate change is making a measurable impact on the distribution of many organisms. The populations of some species are disapearing or becoming more fragmented, increasing extinction risk, others are actually expanding their range north with the increasing temperatures. Insects - and particularly butterflies - are very sensitive to changes in climate, and amongst the winners of climate change is a lovely, tiny butterfly, the Brown Argus, Aricia agestis. In the last few days, I have spotted this butterfly in two new locations in East Yorkshire, including my local wildlife garden, where it is unlikely I would have overlooked it, indicating recent colonisation.
Distribution of Brown Argus (Aricia agestis) in Britain. Black circles show that the species was present in 1970–1982; open circles show newly colonised areas (1995–1999 records, not present in 1970–1982). Circles represent 10 km grid cells (from Menéndez et al 2008)

This species has increased markedly in range in the U.K in the last 30 years, expanding around 10 km per year since the early 1990s, reverting a previously declining trend. This could be seen as a direct response to climate change. But the story is not that simple, the positive response to temperature has been facilitated by changes in the interactions of this butterfly with other organisms. Before the expansion, the predominant caterpillar foodplant of the Brown Argus was the Common Rock Rose, Helianthemum nummularium, a plant that grows on sheltered, south facing, sunny hillsides in chalk and limestone grasslands. Some southern populations used several species from the geranium family, especially Geranium and Erodium. These plants grow on lowland, in cooler habitats than the Rock Rose, so only after temperature increased were these populations able to colonise and exploit these areas. Chris Thomas and collaborators established that expanding populations had a preference to lay their eggs on the more available geraniums, even when they came from populations in hills using Rock Roses. This diet/habitat shift allowed the butterfly to recolonise distant Rock Rose areas, using lowland geranium habitat as stepping stones, which single dispersing butterflies would have been unlikely to reach. A niche model - based on preferred temperature and established food plant - of the predicted range expansion would have grossly underestimated the recent expansion of this butterfly.
 A further complexity stems from an "enemy release" effect. Invasive populations - often translocated by man from distant areas - are hypothesized to expand unchecked as they have left behind their natural enemies: specialist predators, parasites or parasitoids might be absent, and generalist ones might not have the right "search image" for them. Rosa Menéndez and her collaborators tested if this applied to an expanding native population, where the distance travelled from the nearest population is smaller, and there are related species whose parasites might also infect them. They used the Brown Argus and its parasitoids as models. The Brown Argus shares its range with a very common and related species, the Common Blue, Polyommatus icarus, and four parasitoids use both species as host, therefore there is potential for the parasitoids to use the expanding butterfly. They compared the rates of parasitism of old established populations and newly colonised populations. Although both were parasitised by a similar number of parasitoid species (old, six parasite species, new, five), the new Brown Argus populations had an overall lower parasitism rate than the established ones.


Observed parasitism (%) of Aricia agestis caterpillars (i.e. sum of parasitism by 
all parasitoid species) during the first generation in 2004 populations that differ in the 
position within the butterfly range (established vs. new parts of the range). Values are mean + SE and numbers within bars show sample sizes (numbers of caterpillars collected) (from Menéndez et al 2008)

The northward expansion of the Brown Argus is therefore not a direct response to temperature, but the result of a complex interaction including both a diet shift and a partial release of their parasites. This complexity of the biological interactions of each species makes it even more challenging to predict the responses of species to climate change.

MENÉNDEZ, R., GONZÁLEZ-MEGÍAS, A., LEWIS, O., SHAW, M., & THOMAS, C. (2008). Escape from natural enemies during climate-driven range expansion: a case study Ecological Entomology, 33 (3), 413-421 DOI: 10.1111/j.1365-2311.2008.00985.x
Thomas CD, Bodsworth EJ, Wilson RJ, Simmons AD, Davies ZG, Musche M, & Conradt L (2001). Ecological and evolutionary processes at expanding range margins. Nature, 411 (6837), 577-81 PMID: 11385570

Tuesday, 26 July 2011

Bug babies leave their siblings

After at least ten days clustering together on top of their egg cases, the 28 Green Shield Bugs, Palomena prasina, nymphs finally left their siblings after moulting into a greener instar. This is the sequence of events:
20/07/11 All have now moulted into the greener 2nd instar
22/07/11. The nymphs start to disperse in the morning.
22/07/11. After an hour, only three reluctant nymphs remain on the egg cases. In the evening they had all dispersed. 
Some of the adventurous nymphs. I found one a meter away from the egg cases.

Saturday, 23 July 2011

Parasitic wasps turn ladybirds into their bodyguards

ResearchBlogging.orgI have covered the ladybird parasitoid Dinocampus coccinellae before. Some recent research, however, has uncovered some fascinating aspects of this little wasp's manipulation of its host behaviour. The parasitoid wasp, below, injects a single egg on a ladybird using its ovipositor (visible in the top photo of a just emerged D. coccinellae).
After hatching, the larva feeds on its host internal organs, and after about 20 days, she emerges from the ventral plates of the ladybird to pupate. She spins a cocoon that tethers the ladybird to the substrate (top photo) and pupates inside. Unlike many parasitoids, Dinocampus does not kill its host. But the ladybird cannot escape, not only she is tethered, in addition, before emerging from the ladybird's body, the larva is thought to produced some chemicals that affect the ladybird's brain and compels it to sit still, and to twitch when disturbed. The parasitized ladybird colours and twitching were through to afford the parasitoid some protection from predators while in the cocoon. Fanny Maure and her collaborators provided the much needed evidence for this hypothesis in some laboratory experiments. They infected ladybirds - Coleomegilla maculata, a Canadian species - with Dinocampus coccinellae, and once the cocoons were spun under the ladybirds, they split the coccoons into three groups. In the first group of cocoons, they removed the ladybird, in the second, they killed the ladybird and in the third they left the ladybird untouched in the usual position on top of the cocoon. Then they exposed their cocoons to a predator, third instar green lacewing larvae Chrysoperla carnea and counted how many cocoons were predated in each group.
Percentage of Dinocampus coccinellae cocoons eaten by larval green lacewing, Chrysoperla carnea, when parasitoid cocoons were exposed alone, covered by a dead ladybird (Coleomegilla maculata), or attended by a living ladybird. Probabilities were obtained using the Fisher exact test, ***p , 0.0001. Numbers refer to sample sizes (from Maure et al 2011).

Parasitoid cocoons alone or sheltered with a dead ladybird suffered significantly more predation by lacewing larvae that did those protected by living ladybirds, supporting the hypothesis that the parasitoids manipulate the ladybird's behaviour to their own advantage, effectively converting them into their own bodyguards. The ladybird protective colours made little difference, although these are thought to protect against bird, not insect, predators.
  Presumably, there must be a cost to the larvae to manipulate the ladybird. She must left the ladybird alive and produce chemicals to make it into her bodyguard. Maure and coworkers also tested this, by measuring the relationship between the ladybird lifespan once the parasite emerged and the survival and fecundity of the parasite. Their results show a significant negative correlation between the ladybird lifespan - 25% survived the parasitoid emergence - and the number of mature eggs the parasitoids had in their bodies after emergence as adults. This suggest that indeed there is a cost to making your host into a bodyguard. Overall, though, it must compensate the parasite to shield itself with the live ladybird in terms of predator avoidance.

Maure F, Brodeur J, Ponlet N, Doyon J, Firlej A, Elguero E, & Thomas F (2011). The cost of a bodyguard. Biology letters PMID: 21697162

Friday, 22 July 2011

Shelter and food for a cold leafcutter

I pity the leaf-cutter bees on cold or wet days. They really are sun-loving bees and when the weather is not to their liking they hide in the bee hotel, peeking out of the holes, hoping for the sun to appear. I found this cold male Megachile willughbiella clinging to a hardy geranium flower after a shower a few days ago. Geraniums are one of their favourite flowers, and they also makes a handy umbrella.

Thursday, 21 July 2011

Sexing Lesser Stag Beetles

There appears to be a healthy Lesser Stag beetle population in the neighbourhood. Only in my street, I have come across at least six individuals (unfortunately, two of them had been squished on the pavement) in four years. So far, however, I had only seen females, and I was pleased to find a fierce-looking male this morning. This species is often mistaken with Stag Beetles. But Lesser stag beetles are smaller and uniformly black-grey with fine puntuated bodies. They have strong legs with teeth which they use for digging, especially the females, and, when disturbed, they crouch and retract their legs and antennae under their bodies. Although they are not as easy to sex as the Stag Beetle, males and female Lesser Stat Beetles can be told apart based on several features. First, males have larger mandibles, with a rounded knob on them. Females have two characteristic small bumps on their forehead, between their eyes. The third one is that male heads are wider, almost as wide as their thorax, and therefore their mandibles are also set wider apart. Based on the photos and info I've seen, it appears to be a lot of variation on body size (from 20 to 32 mm) and in knob size in males.

For lots of information about the life cycle of the Lesser Stag Beetle and relatives visit Maria Fremlin's website.

Ants tending aphids

Ants have a sweet tooth. They gather nectar from flowers, buds and nectaries but also farm animals to obtain their sweet honeydew. These farmed animals are scale insects and aphids. Ants tend the aphids (above), protect them from their predators and parasites and keep them together for easy "milking". To obtain the honeydew produced by aphids, ants stimulate them with their antennae, after which the aphid will secrete a droplet of sugar rich liquid. These ants are tending groups of aphids on an Iris leaf. To soften the built-in flash light I put a piece of kitchen paper in front of it, holding it with my left finger.

Tuesday, 19 July 2011

Small white or small ultraviolet butterfly?

ResearchBlogging.orgGraced with a few black spots and a shade of yellow in their underwings, the plain wings of white butterflies contrast with the colourful and rich patterns of other butterflies. Unfortunately, this is a reflection of the limitations of our visual system. Male and female Small White butterflies, Pieris rapae, have different upper wing colours, especially in the ultraviolet (UV) spectrum: males absorb UV strongly but reflect most visible light, so they look a brighter white than females to us, but have a dark tone in the UV spectrum, which we cannot see.
A Small White bilateral gynandromorph, with visible female coloration on the left and male coloration on the right (top). Below, a false-colored representation of how these wing colors might be perceived by small whites, which are able to see UV light (photo courtesy of Nathan Morehouse)
Wing colour patterns in pierid butterflies, the family of the Small White, depend on beads made up of pigments called pterins, which are deposited on wing scales, and in the Small White are UV-absorbing. Males vary widely in their brightness and UV reflectance. Males able to produce more beads have darker UV patterns and appear brighter to our eyes. The amount of pterins a male can produce depend of the diet they had as caterpillars. Pterins need a lot of nitrogen to produce - they are the most nitrogen-rich pigment in animals - and the caterpillars can be nitrogen limited, so a brighter male is an indication of a good caterpillar diet. A brighter male also is also expected to be more desirable to a female, as during mating, male white butterflies transfer nutrients to the females in the form of infertile sperm, a nuptial gift which will increase the females life expectancy and therefore will be able to lay more eggs. A male with a higher quality diet can afford to be brighter and to produce bigger and more nutritious nuptial gifts.
 These butterflies are also able to see UV patterns, they have a rich repertoire of visual receptors in the short wavelength, including three types of photoreceptors that peak at UV, violet and blue. Crucially, being aware of their ability both to emit and detect UV allows us to understand their mating behaviour. Nathan Morehouse  and Ronald Rutowski carried out some elegant experiments to test the hypothesis that females choose males with more contrasting UV patterns. They carried out two experiments, in both of them they used lab-reared virgin females, which they presented with some males in a large cage. In the first experiment they used males that were from wild origin, and therefore had a natural range of colour patterns, in the second experiment they used laboratory reared males, but dipped the males' wings in a chemical that partially removes the beads, this way they created a range of variation that mimicked the natural one, but removing other possible confounding effects such as age, nutritional state, effects of encounters with predators or mating history. They removed the mated males to carry out measurements and they allow each female to mate three times. Then they also measured males that hadn't been mated. Females are able to exercise mate choice as they can adopt the "mate refusal posture" by which they lower their wings and raise their abdomen as shown in the photo below when they don't want to mate. Males showcase their wings during their ritualised courtship flight
Courting Small White butterflies. The female, underneath the male is rejecting him by lifting her abdomen and lowering her wings.
Their experimental results (below) together with further modeling of the female's visual system indicated that females, as expected, prefer to mate with brighter males. Sexual selection therefore favours brigher males.

Spectral reflectance of male and female Pieris rapae in study 1 (A) and study 2 (B). Average female phenotype (dashed lines), average mated male phenotype (solid lines), average unmated male phenotype (dashed and dotted lines), and minimum and maximum male values (dotted lines) are displayed. Histograms to the right are for all males, with the proportion of mated males (solid region) and unmated males (open region) indicated in each bin (from Morehouse & Rutowski 2010).
 However, not everything is rosy (or ultraviolet if you wish) for these males, as the same colour patterns that make males more attractive to females, make them more visible to their main predators, birds, which are also able to see in the UV range. This study shows how sexual selection and natural selection through predators can work in an opposite direction, and reminds us that beauty is in the eye of the beholder.

Morehouse NI, & Rutowski RL (2010). In the eyes of the beholders: Female choice and avian predation risk associated with an exaggerated male butterfly color. The American naturalist, 176 (6), 768-84 PMID: 20942644

Mating buff-tailed bumblebees

Next to a busy road, by the base of a tree, surrounded by concrete and oblivious to the noisy traffic, this pair of White-tailed bumblebees were mating this morning. The queen lying motionless, a bit sideways, the male tickling her rhythmically with his legs. I have been taking some videos with my camera lately to record some unusual, or more common bug behaviour. I hope this works as it is the first time I upload a video to BugBlog.
* * *
I wrote the piece above almost 5 months ago, on the 19th of July, when I saw the bumblebees mating. I tried, and miserably failed to upload a video to YouTube. Here it is, finally posted. Thank you Crystal Ernst! More to come.

Saturday, 16 July 2011

Birds and ant swarms

In July and August, typically in sunny days after rains, swarms of reproductive Black Garden Ants (Lasius niger) - winged queens and males - emerge from their nest to mate and start new colonies. Workers also come out en masse and run around the entrance of the nest, looking agitated. I had often noticed this and wondered why do workers did this, until yesterday, watching a Blackbird feeding on the winged ants coming out of their nests, realised why. The Blackbird run close to the entrance, fetched a winged ant and run away. The bird repeated this several times and was obviously being stung or sprayed by the ants around the nest, but still wanted to feed and its back-and-fro behaviour was evidence of the - at least partial - success of the frantic workers keeping predators at bay. Winged ant have many predators. Some casually feeding on the winged ones, others opportunistically making use of a plentiful, although ephemeral, bonanza. A range of birds fall in the latter category, starlings and sparrows feed on the winged ants - sometimes using fly-catcher techniques - and seagulls have been seen feeding on them up in the sky. While reading a paper on this, I remembered that last year, on the day the ants emerged, I looked up in the sky and saw many small flying things and thought they might be the flying ants. When I looked more closely I saw they were seagulls, and was surprised at how many there were, well over a hundred, soaring very high up. I took a shot (below) and forgot about it. They were most likely feeding on the winged ants that had been carried high by thermals in their swarming mating flight.
Seagull flock feeding on swarming ants (26/07/10)
This is the nest in the bottom right hand corner of the top photo
Workers around a nest with winged ants emerging (26/07/10)

James Baird and Andrew J. Meyerriecks (1965). Birds Feeding on an Ant Mating Swarm. The Wilson Bulletin, 77 (1), 89-91.
Gilbert S. Grant (1992) Opportunistic Foraging on Swarming Ants by Gulls, Shorebirds, and Grackles. The Chat, 56, 80-82.

Friday, 15 July 2011

A celebration of butterflies

I have gone through my files and made a selection of common butterflies to celebrate these beautiful insects in anticipation of the Big Butterfly Count, that starts tomorrow (16th to 31st of July) . This year it will last two weeks so there is more chances you can be out during good butterfly weather. You need to count what butterflies - and moths - you see in 15 minutes during a sunny spell. You can complete as many surveys as you want - from different days or different places - and you have time until the end of August to submit your records online. Click in the photo to start the slideshow.

Thursday, 14 July 2011

Poisonous bug babies cluster together

ResearchBlogging.orgThese newborn green shieldbugs, Palomena prasina, look most unlike adults. They have a bright black-red warning colouration in their first instar, for a few days they cluster tightly together on top of their egg shells. After moulting into their second instar they change colour to green and black and they disperse away from their siblings. All shieldbugs, including nymphs have stink glands between the first and second pair of legs. If handled roughly they can release repellent chemicals and they are often brightly marked. But why do these bugs cluster together?
 The contrasting black and yellow or black and red patterns of Cinnabar mothsladybirds, Burnet moths, bumblebees and wasps are visual signals to potential predators indicating that the animal is distasteful, poisonous or dangerous in some way. The predator, having had a nasty encounter with the aposematic organism learns to avoid it. But how does does aposematism evolve in the first place? You would think that the first aposematic individual either dies or is injured in the process, so it cannot be though natural selection, right? One possibility, first suggested by Sir Ronald Fisher in 1958 is aggregation of related aposematic organisms:
For, although with the adult insect the effect of increased distastefulness upon the actions of the predator will be merely to make that individual predator avoid all members of the persecuted species, and so, unless the individual attacked possibly survives, to confer no advantage upon its genotype, with gregarious larvae the effect will certainly be to give the increased protection especially to one particular group of larvae, probably brothers and sisters of the individual attacked. The selective potency of the avoidance of brothers will of course be only half as great as if the individual itself were protected; against this is to be set the fact that it applies to the whole of a possibly numerous brood
Fisher's hypothesis of kin selected aposematism has been questioned recently. Although aposematic organisms tend to be gregarious, phylogenetic analysis suggest that aposematism evolved before gregariousness, so aposematism makes gregariousness easier to evolve, and not the other way round.
 Birgitta Sillen-Tullberg carried out some elegant experiments showing that aposematism can give direct benefits to the individual, and that kin selection is unnecessary. She presented hand reared Great Tits (Parus major) with two colour forms of the same bug species (Lygaeus equestris), one grey and black (cryptic), and the other - the common form-  red and black (aposematic). A group of tits was presented with cryptic prey and another group with aposematic prey in 11 trials per bird. Great Tits learned to avoid both cryptic and aposematic prey - remember both are equally distasteful - but attacked cryptic prey more readily from the first trial.

In addition, when attacked, aposematic prey survived more, indicating that the tits were more wary when attacking it.
Being grouped, though, can confer further advantages. Gabriella Gamberale and Birgitta Tullberg carried out experiments testing the effect of grouped versus solitary prey - bugs, Spilostethus pandurus - on learning avoidance by predators - chicks in their experiments. Chicks learn to avoid aposematic shieldbugs in fewer predation attempts, and were less likely to attack twice they are aggregated than if the prey is solitary. They concluded that gregarious aposematic prey are a more effective signal for the chicks to learn, the reasons why this could be are still unclear.

Fisher, Ronald A. (1958). The Genetical Theory of Natural Selection Dover Publications, Inc. Other: 0-486-60466-7
Sillen-Tullberg, B. (1985). Higher survival of an aposematic than of a cryptic form of a distasteful bug. Oecologia, 67 (3), 411-415 DOI: 10.1007/BF00384948
Gamberale, Gabriella, & Tullberg, Birgitta S. (1996). Evidence for a more effective signal in aggregated aposematic prey. Animal Behaviour, 52 (3), 597-601 DOI: 10.1006/anbe.1996.0200

Tuesday, 12 July 2011

Face off

ResearchBlogging.orgEctemnius wasps are skilled fly hunters. Not only they hunt flies, but some species specialise in hoverflies, those masters of controlled flight. Like their prey, Ectemnius wasps are able to hover. As their large eyes suggest, they hunt visually and inspect flower patches that hoverflies frequent, hovering a bit, changing body direction, inspecting their terrain thoroughly. Once they detect a hoverfly, they try to approach from behind, and when at about 10 cm they aim and attack. Ectemnius provisions its nest - dug in dead wood - with hoverflies, which will serve as food for its larvae. The adults themselves feed on nectar. I was trying to photograph this digger wasp stalking hover flies, when it came across a male Syritta pipiens. The tiny hoverfly male, which often confronts other hoverfly males on this patch of wild rocket, instead of fleeing, it confronted the wasp, mirroring the predator movements and keeping his distance, both insects hovering perfectly still in front of each other for a few moments. Surprisingly, the wasp did not attack the fly and just moved on. Some insects have been shown to display a stealth strategy called "motion camouflage" by which an individual (the shadower) can conceal its movements to another individual (the shadowee) by maintaning its position in the retina of the shadowee. The shadower then appears as an stationary object from the point of vision of the shadowee. Some male hoverflies (and Syritta pipiens in particular) use this flying strategy to track females undetected and dragonflies use it to avoid being detected when intruding in other territories and it is also suspected to be used by visual insects when approaching prey. A range of models have been developed to simulate this strategy. Unsurprisingly, engineers are developing motion camouflage strategies to be applied to robots, satellites or with military purposes.
 According to Justh & Krishnaprasad:
Motion camouflage can be used by a predator to stealthily pursue the prey, but a motion-camouflage strategy can also be used by the prey to evade a predator. The only difference between the strategy of the predator and the strategy of the evader is that the predator seeks to approach the prey while maintaining motion camouflage, whereas the evader seeks to move away from the predator while maintaining motion camouflage.
I wonder if this was the case in the above photo. A temporary stale mate, but the prey got away.

Justh, E., & Krishnaprasad, P. (2006). Steering laws for motion camouflage Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 462 (2076), 3629-3643 DOI: 10.1098/rspa.2006.1742
Mizutani, A., Chahl, J., & Srinivasan, M. (2003). Insect behaviour: Motion camouflage in dragonflies. Nature, 423 (6940), 604-604 DOI: 10.1038/423604a

Monday, 11 July 2011

Fresh Holly blue shows its tongue

July is peak time for butterflies. What up to mid June seemed like a poor butterfly year is gearing up to a great one. Just today I watched 8 species locally. The most striking of them was this freshly emerged Holly Blue male. It is the first individual of the second generation I see this year. It basked in the morning sun in a front garden, and - unusually for this species - it sat with wings fully open for a while. Once warm, the butterfly closed its wings and fluttered onto another perch and stretched its tongue.
A more usual sitting posture for a Holly Blue, with closed wings
The butterfly with its short tongue stretched
Tongue length in butterflies is correlated with body length, so it is not surprising Lycaenids, the family to which the Holly Blue belongs, being small butterflies, have short tongues, around 8 mm. Whites and Brimstone and the Nymphalids have longer tongues, around 15 mm. For their length, some moths (such as the Hummingbird Hawkmoth) have very long tongues, 28 mm. The following table from Pollination and Floral Ecology by Pat Willmer illustrates the length differences between some butterflies and moths.
Tongue length determines the maximum depth of a flower corolla that a butterfly can take nectar from. Short tongued species prefer shallow flowers, often composite ones like brambles, tansy, hemp agrimony or dandelions.

Saturday, 9 July 2011

Emerging harlequin ladybird

I collected 50 ladybird pupae (above) a couple of weeks ago. The idea was to wait and see what emerged from them to send records to the Ladybird Parasite Survey. After 6 days, 46 Harlequins had emerged, and from 2 of the remaining some tiny maggots of the parasitic phorid fly Phalacrotophora. Having so many ladybirds emerging at home meant I had a good chance to catch one of them emerging, something I had never seen before. I saw two, one of them almost right from the beginning, and this series of photos documents it. The whole process took about 10 minutes. In the next shot, the ladybird has broken the pupal skin and the pupal buds containing both pairs of wings are erect.
...she finally walks out. 
The ladybird then waits next to its pupal skin until she has hardened a bit and extends her wings, which are still yellow. You can see how the ladybird gets her spots in this post.

Friday, 8 July 2011

Darting Small skippers

A grassy area in the little wildlife garden near where I live is managed like a meadow, cut once a year. The grass is long and lush now, peppered with a range of wildfowers. One of the insects that benefits from this arrangement is the Small Skipper, Thymelicus sylvestris. The males of this golden brown, little butterfly dart around the meadow, stopping to feed or sunny themselves occassionally. The larval food plant of this species is Yorkshire Fog, a common rough grass. The adults emerge in mid June and fly in a single generation until August. They like to feed on clovers, bird's foot trefoil, restarrows, knapweeds, thistles, brambles and hawkbits. This is another butterfly species thought to have benefited from recent climate warming in the U.K. It now inhabits most of England and Wales, with its range having moved north about 100 km in the last 25 years.
A male, the same individual as above, resting on Bird's Foot trefoil. Male skippers can be distinguished from females by their "sex-brand", a dark like in the middle of their forewings.

Thursday, 7 July 2011

Brown-Lipped Snails

ResearchBlogging.orgThe Brown-lipped or Grove snail, Cepaea nemoralis has received a lot of attention by evolutionary biologists for more than a century, due to their strikingly variable shell colour - what is called colour polymorphism. In the decades of the middle of the last century it was a very popular research organism. The shiny shell can be yellow, pink or brown. Over each of these background colours there can be no bands, one band or five bands, and the bands can also be fused and be of variable width. The snail above, which we found yesterday feeding on the fallen leaves on the garden path, is a yellow/one banded one. This polymorphism happens within the same population, but what puzzled biologists was the occurrence of sharp changes in the frequency of colour forms from one population to the next, and these differences seem to persist with time. This phenomenon was called "area effects". Many explanations have been proposed through the years to explain how the polymorphism is maintained and how area effects come to be, from differential predation (especially by song thrushes), adaptation to microhabitat, or other forms of selection to chance effects due to colonization after the glaciations, genetic linkage, dispersal between populations, etc. Many of these factors are not mutually exclusive and seem to have different importance depending on the population.
 We found the shells below in the beach in Spurn Head a few years ago, all in a small area. They are a bit bleached by the sun, but you can see yellow and pink snails and three types of banding patterns.
The Brown Lipped snail can be found from dunes to roadsides, gardens and closed woodland. It can live up to 8 years old. They prefer to feed on dead vegetation than fresh, and on average, only 9% of its diet is fresh vegetation, although this percentage can increase during dry spells.

Cain AJ, & Sheppard PM (1954). Natural Selection in Cepaea. Genetics, 39 (1), 89-116 PMID: 17247470
Davison, A., & Clarke, B. (2000). History or current selection? A molecular analysis of 'area effects' in the land snail Cepaea nemoralis Proceedings of the Royal Society B: Biological Sciences, 267 (1451), 1399-1405 DOI: 10.1098/rspb.2000.1156
Paul J. Mensink & Hugh A. L. Henry (2011). Rain event influence short-term feeding preferences in the snail Cepaea nemoralis Journal of Molluscan Studies. DOI: 10.1093/mollus/eyr011

Tuesday, 5 July 2011

Amber Snail Puzzle

ResearchBlogging.orgWhile removing an old pot containing a lot of grass and a dead Agapanthus, next to a rainwater filled pot, I stumbled upon this little snail. I was quite surprised as initially, I thought it was a pond snail, but closer inspection revealed the tell-tale eyes-on-top-of-tentacles characteristic of land snails and slugs, while aquatic snails have their eyes at the base of their tentacles. After sifting through a Molluscs guide I found out it was a Common Amber Snail, Succinea putris. Although not aquatic, it usually lives near water or in waterlogged habitats, and it is often found on the stems of aquatic plants. It cannot retract its body completely inside the shell, and the lower pair of tentacles is vestigial. I have no idea how this snail got into our garden, but snails, despite being slow and strongly dependent on humidity, are known to disperse widely. In the Origin of the Species, Charles Darwin believed birds were the most common long range dispersal agents of snails and other aquatic animals and plants. In 1893, Harry Wallis Kew reviewed the dispersal of land and water molluscs, and discusses the evidence for external transport on the feathers of birds:
Sir C. Lyell, remarking on the wide range of Succinea putris, a land-shell which inhabits moist places on the borders of pools and streams suggested that water-fowl might have distributed its ova entangled among their feathers and it seems quite likely that ova of certain terrestrial kinds may be occasionally thus carried, either in the feathers or on the feet of birds; indeed, we have a near approach to proof of such transportal, the Rev. Canon Tristram, as we have seen, having once found ova, believed to be those of a Succinea, upon one of the feet of a mallard shot by him, on the wing, in the desert of Sahara. It is doubtful, however, whether Succinea, from the nature of the localities they often or usually inhabit, ought not, for the present purpose, to be classed with fresh-water, rather than with land-shells. Mr. Darwin suggested that the just-hatched young, possibly, might sometimes crawl upon the feet of ground-roosting birds, and thus get transported; and it certainly seems in the highest degree probable that such is the case, but, as far as I know, no observations in support of such a supposition have yet been made.
A tantalizing possibility, also first put by Darwin, is that of internal transport of organisms in the digestive tract of birds. Many bird species feed on snails, and given that no gastric juices occur in bird's crop, they can potentially survive for a while and maybe be discharged later elsewhere by the bird, or regurgitated by raptor if the bird falls prey to it. Kew stated:
 Twenty specimens of a Succinea, peculiarly packed together, and four of Pupa viuscornvi were once found by Mr. W. H. Dikes in the crop of a bearded titmouse (Parus biarmicus); all the shells, it is said, were uninjured, but it is not stated that any were observed lo be alive.
In 1968, Biggs reported on the recovery of a living Succinea putris from a pigeon's crop at least 8 h after the bird had died. Indeed, although it seems even more unlikely, some snails can survive passage through the whole digestive tract of birds provided the shell is more or less unbroken. This has recently been shown to happen to a small estuarine snail, Hydrobia ulvae, which can survive passage through the digestive tract of Shelducks, and also in some small Japanese terrestrial snails, Tornatellides boeningi a proportion of which were recovered alive in the feces of two species of terrestrial bird they had been fed to.
I don't think any of these forms of dispersal apply to the particular little snail in the above photo. Maybe it travelled on a pot plant we bought some time back in a garden centre, or, stuck to our clothes or shoes during an outing into some wetlands. Maybe, but just that any of the forms of transport Darwin and Kew discussed actually happen to snails shows you don't need wings to fly high.

Biggs, H. E. J. (1968). Succinea putris (L.) in a pigeon's crop Conchologist Newsletter, 24: 36.
Gerhard Cadée (2011). Hydrobia as "Jonah in the whale": shell repair after passing through the digestive tract of shelducks alive. Palaios, 26 (4), 245-249 DOI: 10.2110/palo.2010.p10-095r
Darwin, C.R. (1959) On the Origin of Species. Read the book here.
Kew, H.W. (1893) The dispersal of shells: an inquiry into the means of dispersal possessed by fresh-water and land Mollusca. K. Paul, Trench, Trübner & Co., Ltd. Read the book here.
Shinichiro Wada, Kazuto Kawakami and Satoshi Chiba (2011). Snails can survive passage through a bird's digestive system. Journal of Biogeography : doi:10.1111/j.1365-2699.2011.02559.x