High flyers: Silver Y moths

Yesterday I came across some piece of fascinating research on the silver Y (Autographa gamma), a brownish-grey moth so called for its Y shaped mark on each forewing. This moth is relatively large and is often active by day, with a liking for lavender and other flowers, moving its wings non-stop while feeding.

This is another great summer migrant into the UK and other parts of northern europe, where their caterpillars are often an agricultural pest. Jason Chapman and collaborators used an entomological Vertical Looking Radar (VLR) to detect individual flying insects. This radar is very sensitive and able to assess the high at which each insect is flying, its body orientation and flight speed. They analyzed radar data for nights in August 2000 and 2003, peak season for silver Y returning to their Mediterranean wintering grounds. Using trap data they established that the dominant flying moth species during those nights were silver Ys. Their data shows that this moth selects those nights with favorable wind directions for their migration (SSW) and that they adjust the hight they are flying to where the wind is fastest, usually over 100 m high.

Figure 1 from Chapman et at. 2008. Circular Distributions of Directional Data Obtained during Return Migrations of Autographa gamma Mean directions from each event are plotted (small circles at periphery). The bearing of the solid black arrow indicates the mean direction of the dataset, and the length of the arrow is proportional to the clustering of the dataset about the mean. (A)The mean tracks of high-flying migrant A. gamma during the 42 mass-migration events detected by vertical-looking radar (mean direction = 202). (B) The wind direction at 300 m at both radar sites during the migration periods. (C) The mean flight headings of migrant A.gamma during the 37 events with significant common orientation (mean heading = 205).

More astonishingly, their data shows that these moths compensate for their flight direction when the wind doesn't blow exactly in their preferred heading. This last discovery indicates that silver Ys use a compass. Given that the moths fly during nights when the moon is not visible and in overcast conditions, and their visual acuity, they could exclude a moon compass and a star compass. They conclude that the moths must have a magnetic compass, maybe adjusted by the sun at sunset. This fantastic technology illustrates how complex and plastic insect behaviour is, and how relatively slow flyers can get to their winter grounds in a few nights of flight.

More informationCHAPMAN, J., REYNOLDS, D., MOURITSEN, H., HILL, J., RILEY, J., SIVELL, D., SMITH, A., & WOIWOD, I. (2008). Wind Selection and Drift Compensation Optimize Migratory Pathways in a High-Flying Moth Current Biology, 18 (7), 514-518 DOI: 10.1016/j.cub.2008.02.080

Warming up painted lady

Cloudy, with intermittent showers today. A cold Painted Lady sat 'shivering' on a bush in the garden and allowed me a close approach. The shivering appearance was due to the butterfly revving its flight muscles, what I had never seen before. I have to apologize - to the butterfly - that I had to use flash, as it was dark and I wanted to emphasize the effect of its wings movement. A few moments later, the butterfly flew away.

A view of the Painted Lady's wing underside.

On this frontal shot the first modified pair of legs are visible just under the butterfly's eyes. 

Emergence of Winged ants

For a couple of weeks now, sunny spells after showers bring out a nervous anticipation in ant colonies. The workers come out en masse and run frantically around the colony entrance holes, often in cracks on street pavements. I have stopped a couple of times to watch this but so far no sign of winged queens and males. Yesterday though, we got the first glimpse of emergence of winged ants (Black Garden Ant, Lasius niger). Emergence happens during July and August and sometimes is very synchronic around the country. Workers seem to keep them in, while they stand high on their front legs, as if sniffing the air with their antennae, appearing to check that everything will be fine for their reproductive brothers and sisters. They have to sort out predators - sparrows and many other insect eating birds love them - during their mating flight. Queens will mate and then find a suitable hole where to dig their first colony. They might live for over a decade, sheltered in their nest taken care of by their daughters. Males will die shortly after mating.

Home-grown Painted Ladies

All of a sudden, Buddleia blooms across the city today were decorated with fresh-looking bright coloured Painted Ladies (Vanessa cardui). The contrast with the faded, worn first individual I photographed this year (see this previous post and also an extreme example here) was stark. Most of today's butterflies were likely to have been born in the U.K., the offspring of the migrating individuals. It is unclear how many generations of Painted Lady happen every year, as there is a lot of overlapping. According research carried out by the Spanish researcher Constanti Stefanescu, the whole cycle outdoors takes 6 to 8 weeks depending of the temperature, and he estimated 3 to 4 generations for NW Spain. The number of generations must be more limited here, with the cooler climate, and is likely that these fresh-looking butterflies will become the returning generation and they are not interested in breeding anymore, but in fattening up for their lengthly return to North Africa

Feeding against the sky

A fresh Painted Lady sunbathing on a wall

More information
Stefanescu, C. (1997) Migration patterns and feeding resources of the Painted Lady butterfly, Cynthia cardui (L.) (Lepidoptera, Nymphalidae) in the northeast of the Iberian peninsula. Miscel.lania Zoologica, 20: 31-48.

What are slugs up to on your kitchen floor?

Late last night I went to the kitchen and found a couple of large yellow slugs entwined on the kitchen floor. I dashed back to the front of the house to grab the camera but in the few seconds that took me do do it - it is a well rehearsed sprint of mine - they had started going their separate ways. The sudden flash of light when switching on the kitchen light must have shocked them and they went shy. The only indication they had been together was a circle of slime on the tiles. Should I carry my camera with me as I walk around the house? I sometimes think so. I knew nothing about the yellow slug mating habits. The yellow slug Limax flavus is not as good-looking as its relative the Leopard Slug, Limax maximus of fame due to its acrobatic sex featured in David Attenborough's Life in the Undergrowth TV series (see also the fantastic photos in Snail's Tails). I found very little, well, yes, as snails they are hermaphroditic and exhange sperm, although self-fertilisation is not unheard of. I also found a clip of the start of courtship, which happens on the ground. So I am afraid I will have to wait and see if I can catch them again. I cannot believe I am going to look forward to see slugs at home.

The sunspot owners: Speckled Wood butterflies

Male Speckled Wood perched on his sunny spot

The Speckled Wood (Pararge aegeria) butterfly is largely a new millennium butterfly in East Yorkshire. Probably due to the warming climate in the British Isles, the range of this butterfly is gradually increasing north. I saw the first Speckled Wood in Hull in a disused cemetery with large trees and lush undergrowth in 2005. This is a woodland and hedgerow species, not often found feeding on flowers. Adults feed mainly on tree canopies on honeydew, a lovely name for the sugar-laden aphid and scale insect sticky secretions. The most obvious individuals are males, which defend sunlight spots on the woodland floor. They rest on exposed, sunny leaves and inspect any butterfly or insect that passes by. Other butterfly species are briefly checked before the males come back to their resting place, females are courted, and intruding Speckled Wood males that come down from the tree canopy are chased in a brief spiral flight. This territorial behaviour was investigated in a classic paper by Nick Davies in woodland near Oxford. He visited the woodland daily and carried out lots of simple experiments with Speckled Wood individuals marked with colour spots. This way he was able to describe in detail the movements of each individual butterfly. Individual males spent all day in a sunny spot in the woodland floor, fluttering around and perching in it, and following faithfully the sunny spot as it moved though the day on the woodland floor. One of the most interesting findings of this study is that every time an intruder entered a sunny spot, and was involved in a 'spiral flight' with the owner, the intruded ended up retreating to the tree canopy and the resident took its position in the sunny spot. In all the spiral flights observed, over 200, the resident always won regardless of his condition. Davies concluded that the spiral flight is not a 'fight' but a courteous exchange of pleasantries: "to put it anthropomorphically, the owner says 'I was first here and the intruder says 'Sorry, I didn't know there was anybody occupying the sunspot, I'll retreat back to the canopy'. The reason the intruder comes down into the canopy is that it doesn't know the spot is taken. Davies carried out some experiments in which he introduced a male into an already occupied sunspot without the resident male noticing (he remarks he failed frequently, as the resident male seems to be always on the lookout for intruders). In the five occasions he succeeded, the spiral flight escalated and was more lengthy than usual, as both males regarded themselves as the territory owners. Only a few seconds of residency were enough for them to consider themselves the spot owners. Males were competing for the sunny spots and the tree canopy males readily occupied empty spots. The reason for this competition is that females often visit these sunny spots and therefore, males defending a sunspot are more likely to mate. The males on the canopy do not defend a territory but patrol the trees up and down in search of the rarer females. 

Female Speckled Wood

Male perched on his sunny spot

Mating bumblebees

This morning, just before 9:00 we saw a pair of mating Bombus terrestris on the pavement. At first I thought they had been squished, or rather, that the female had been, as she was lying a bit sideways and was motionless, while the male seemed actively thrusting. I got a stick to move them out of the way (I saw a pair of Bombus lapidarius squished on the pavement last week!) and the female then revived and started jumping trying to fly, possibly warming up. She did a few jumps with the male on tow. I thought they were going to end up on the road. Just then, she took off and flew high, straight over the trees at the other side of the street. A truly impressive sight! I felt very lucky to have witnessed the event, and even luckier to have been able to take a few shots.

Hovering high

Today I read a very interesting paper by David Lack (of fame as an ecologist and evolutionary biologist for his bird studies and his books, of which 'The Life of the Robin' is my favourite). He described his observations on a day of October on top of a high Pyrenean pass. In addition to various flock of migrating birds, he accounts in detail how large numbers of butterflies (mainly Red Admirals and Clouded Yellows) and Common Darter dragonflies (Sympetrum striolatum) steadily crossed the pass towards the Spanish side. That birds migrated had already been well established, but insect migration was then a much more recent, still controversial phenomenon.Lack felt provileged to have witnessed such extraordinary phenomenon, and the feeling was probably enhanced by the beauty of the surrounding mountains, at 2227 m altitude. He wrote "Once in a lifetime perhaps, the ecologist is translated back into a naturalist, through chancing on a spectacle which combines grandeur with novelty. Such was our fortune at the Port de Gavarnie on 13 October 1950."

Cirque du Gavarnie (Photo by Marando-fr, Wikipedia Commons)

Lack's was the first account of hoverflies migrating. In his own words:

Not until we had been at the pass for over an hour did we realize that another insect was migrating, so we do not know whether it was passing from the start. This was a hoverfly, the two collected specimens being males of Episyrphus balteatus. All the other individuals looked the same, and we have no reason to think that any other species was present. The syrphid flies, like the dragonflies, flew steadily forward WSW. against the wind, keeping extremely close to the ground, where the wind was, of course, weaker. Very occasionally one settled for a moment, but otherwise they travelled steadily onward. An estimate of numbers was impossible, but at a guess they were at least twenty times, and perhaps a hundred times, as numerous as the dragonflies. They were the most remarkable migrant of all.

Today there were many E. balteatus in the garden. To think that such tiny, flimsy looking hoverfly, is able of such powerflul climbs and long voyages! It is just plainly amazing.

Episyrphus balteatus on Cat's ear (summer 2006)

A close up. Today, on an ice plant.

Reference
Lack and Lack (1951) Migration of insects and birds through a Pyrenean pass. Journal of Animal Ecology 20:63-67.

An unexpected humming visitor

Yesterday, while taking photos of the resting Wool-Carder bees, I was nicely surprised by the low humming noise coming from a Hummingbird Hawkmoth, Macroglossum stellatarum. It was feeding high up in the blossoming buddleia. Fortunately I had the camera with me (I don't let it out of my sight these days!) and managed a few shots. The one on top is the best. Like the Painted ladies and silver Y moths, they are migrating insects from southern latitudes, which tend to come in warm weather and tend to appear on the same summers.

Graph showing my local records for three migrant species as year totals. The scale is logarithmic and I have replaced 0 by 0.1 to allow for this.

Hummingbird Hawkmoths take their name from their hovering flight. As other hawkmoths, they have long proboscides and do not land on flowers to feed, but just hover in front of them, darting sideways to the next bloom. They are active during the day and at dusk, which makes them easy to observe, unlike many nocturnal moths, including some of the same Hawk-moth family (Sphingidae). Hummingbird hawk-moths have fast flight and small wings, so, due to their high energy demands they prefer nectar rich flowers. My records are in Buddleia, Caryopteris, lavender, Centrarthus ruber and Ceanothus.

Hummingbird hawk-moth feeding on buddleia at sunset (Sep 2003)

 Hummingbird hawkmoths have been the subject of learning experiments carried out by Almut Kelber regarding flower colour and design. They are as good learners as bumblebees, much better than the butterflies tested, which had strong innate preferences. Although the hawk-moths have a innate preference for blue flowers, they are eager to try new colors and easily learn to associate different colours with food rewards. Given that they are relatively long-lived (up to 4 months in the laboratory) and strong migrants, this flexible learning behaviour might give then the ability to sustain their high energy requirements from different, seasonally or locally changing flower resources.
 If you have any records, Butterfly Conservation is carrying out a survey: Migrant Watch - Hummingbird Hawk-Moth.

Who is the king of the castle?

I am quite keen to recognise individually the wool-carder bees in my garden, especially the males. I think I will be able to understand better what is going on if I can tell who is who. Individuals appear to show quite a lot of variability in the yellow and black markings in the face and abdomen, so that looked promising. In their normal behaviour, the bees are quite fast and unlikely to pose for a frontal shot! However, in colder weather, or at the end of the day the bees are more restive, and often cling to flowers with their jaws. Today I had a chance to take a few portraits of the Wool-Carder bees. It was overcast most of the day and the temperature was around 16-16.5 oC. There was some storms yesterday and the male in charge was looking quite miserable with his hair soaking wet, clinging to the top of a Stachys spike.  Bombus terrestris and B. pascuorum bumblebees were happily feeding around him in the Stachys as if he wasn't there.

Bombus terrestris feeding close to cold male Wool Carder bee

B. pascuorum about to land on the same spike of flowers where the male is resting 

He shook his wings every now and then but was very still. I took quite a few close ups, of his face and abdominal markings. Later on I noticed there were also two females resting - or waiting for warmer weather - nearby. In the middle of the day they all seemed to arouse themselves a ilttle and they started to walk up and down the Stachys spikes feeding, but seemingly unable to fly.
 From the shots (comparing today's with individuals from previous years) it appears that the females have browner faces, and that it is possible that I will be able to see if the top male is overtaken by another later in the summer, most likely through the more visible and variable abdominal markings.

Male abdominal patterns. On the right is this year's male.

Female facial patterns

Male facial patterns. On the left our cold and wet friend

A lesser stag beetle

Other than ladybirds, the occasional carabid or a few weevils, beetles do not figure very high on the list of common garden visitors. I was so pleasantly surprised when on Sunday, while tidying up the garden we came across a Lesser Stag Beetle (Dorcus parellelipipedus). These large, grey-black beetles, related to the Stag Beetle, are not uncommon in the UK, but sightings are rare north of the Humber according to the National Biodiversity Network Gateway. The adults and larvae feed on decaying wood - particularly ash, apple and beech. This is the second one I see in Hull. We live in a street lined with large trees and I collect dead fallen branches - including those from a large ash - from the verges and bring them to our garden for our log pile (we also used those for our bee posts). The log pile (see this for an interesting page on log piles) tends to be full of common critters like snails, woodlice and earthworms, nothing very exciting. Occasionally Digger Wasps nest in the decaying wood and I would like to think this beetle was actually born in the garden.

Painted Lady mass migrations

I have just reported the first Painted Lady (Vanessa cardui) of the year to the Butterfly Conservation Painted Lady Survey. It settled today on my large buddleia, now covered in full bloom, and fed for a log time, fluttering from one bloom to the next (photo above). It has been a long wait considering the species has been on the news for a few months now. Painted ladies are strong flyers and migrate every year into nortern latitudes in search of foodplants and nectar, but migrations vary in their strength several orders of magnitude (see graph).

(From Stefanescu et al 2007)

Mass migration of butterflies occur every 6-10 years, as the last large migrations on this years scale in 1996 and 2003. The last couple of years have been quite poor. This year, in contrast, from a handful of sightings before May, thousands of migrating Painted Ladies were reported in the UK starting from southern England. This butterfly species overwinters in the semidesertic areas of North Africa but also of Mexico and Asia, as it is a cosmopolitan species. Depending of climate fluctuations such as El Nino, higher rainfall than usual in these regions make their larval foodplants - many, but mainly mallow and thistles - flourish, together with the butterflies. The newly emerged adults then start a northwards migration following their foodplants and nectar. Most records of migrating Painted Ladies are of individuals migrating in a given direction near the ground. However radar data of other migrant butterflies - the Monarch and the Red Admiral - documenting them migrating from 1000-3000 m high, sometimes rising with thermals and then gliding down with the aid of tail-winds towards their destinations, an energy-efficient and faster migration strategy than flying close to the ground. A recent study by Stefanescu and collaborators used an indirect approach to study how Painted Ladies migrate. They tested the idea that Painted Ladies migration from North Africa to southern Europe happens high up in the atmosphere aided by tailwinds. They tested whether butterfly peak records were associated to winds blowing from Africa - winds laden with Saharan dust are common in Spain in Spring. The data showed a clear effect of Northerly winds from North Africa in the sudden appearance of visibly migrating Painted Ladies in many localities of NE Spain. These results indicate that the butterflies use the wind to migrate more economically and doing so often flies high up over the ground. The flights close to the ground might reflect periods during the migration in which wind conditions are not favourable high up. The butterflies fly both by day and night and often over vast distances over the sea (there are records from fishing boats and oil rigs tens to hundreds of miles off the coast. Mysteriously, and contrasting with the spectacular spring migration, there is little evidence of the autumn return migration of the Painted lady -although the suden appearance of high numbers of butterflies in their winter grounds suggests that it does happen, as one could predict based on evolutionary grounds. There is hope that future analysis using radar might reveal if these butterflies return to Africa mostly flying high up, where their movements are difficult to observe and where they take advantage of fast winds. This is what Rebecca Nesbit, who is carrying research into the Painted Lady migration thinks could be the explanation.

White on white

In the last four days I have come across two white butterfly individuals resting on leaves of very similar colour to themselves. If is it just chance or if they are trying to camouflage themselves against their chosen resting place I cannot say, but they made for a nice photographic opportunity.

    

Large white on Stachys lanata, Lamb's ears

Green-Veined white on Phlomis fruticosa, Jerusalem Sage

Predator and prey

The sure destiny of many aphids these days is to end up as an ladybird meal

In the last couple of weeks, the number of ladybird larvae in the garden has increased noticeably. All sizes from tiny newborn larvae to full sized, ready to pupate ones are found on a large variety of threes and shrubs in which, so far, aphids were happily eating and reproducing. Most of these larvae are Harlequins, the new invasive ladybird with generalist feeding habits. I have mixed feelings for this species. On the one hand, as I already wrote in another post it is quite invasive and could compete and affect adversely native ladybirds. On the other, given that we do not use pesticides in our garden the Harlequin aphid-munching could mean I have some nice cherries to eat in a couple of weeks time. I am not for demonising invasive species or believing gloomy, apocalyptic scenarios relating to them. It is us humans who put them here in the first place. The Harlequin was used to control greenhouse aphids and scale insects (biological control gone wrong, again!) and I get the feeling it is here to stay. Lets hope for the best regarding our native ladybirds and enjoy the Harlequin as the beautiful insect it is.

Tiny larvae

Fully grown larvae

Ladybird pupae

A shiny recently emerged Harlequin considering its meal

New males on the block

I have spent a good couple of hours crouching next to my Stachys plant, camera in hand, fascinated by the drama rapidly unfolding around it. And the news is, that the first Wool Carder bee males appeared today. Early in the morning the females (at least three of them) were feeding and gathering wool in their usual way, when one individual started chasing around others. I checked and, yes, it was a male. A beautifully fresh one (pictured above). It gave the impression to rest occasionally on a leaf or stick, but on close inspection he was moving his head incessantly, visually scanning around looking for potential 'illegal' users of his newly declared kingdom. Since the Stachys started flowering on the 11th of June at least three bee species have been more or less regularly feeding on the Stachys. Bombus pascuorum the most common one, then Apis mellifera, the Honey Bee and occasionally Bombus terrestris. Now they are under attack. Attacks today were not very often and the I didn't see any matings, but maybe it's because is the first day. A honey bee was quite persistent and came back several times after being pounced upon by the male. The male moved between the Stachys and the Phlomis, and I managed to see both a male and a female feeding on the Phlomis, the male after a few tentative tries, managed to push the flower open and feed. The female in search of pollen, lifting the upper lip of the flower to expose the anthers. Wool-Carder bees have a special attraction for Lamiate plants (the mint family) and these are the only two flowering in my garden at the moment. The sage and the lavender are not in bloom as yet. After a while I noticed there was a second male. It looked like it was covered in dust, but when I checked the photos they were actually mites! I saw females with mites too, especially around their 'waist'. The male seemed to be a bit bothered by it and keep trying to clean his head. This actually makes both males - if there are not more - easy to tell apart. You can see from the photos.

Honey bee

A sorry-looking male covered in mites

On this shot the density of the mites is very apparent on the same male. The male

 was pushing his way into a Phlomis flower.

And before leaving Wool Carder Bees - for now! - I recently came across a fascinating site, the Biodiversity Heritage Library, a formidable project by which 10 world-leading institutions, including the Natural History Museum and Kew Gardens, are to digitize their library collections. The site now includes over 13,000 books and journals scanned and freely available to download to everyone. It is also fully searchable. It has now become my favourite site to find out old literature about a species - the type that is not usually available in your typical university library. In this site I came across this beautiful drawing of Wool Carder bees, illustrating the size differences between males and females. The illustration is taken from "The Cambridge Natural History", ed. by S.F. Harmer and A.E. Shipley, v 6.

Anthidium manicatum, the Wool-Carder Bee. A, male, B, female.