Forked tailed flower bee on common toadflax

I planted a new bed with native flowers earlier in the year: foxgloves, hedge woundwort, common toadflax, oregano and bird's foot trefoil. It has been very popular with bees and other insects, but there was the one plant that I hadn't seen being visited: the common toadflax, Linaria vulgaris. This relative of the snapdragon has spikes of closed flowers that require some effort for insect to access the nectar and pollen. On top of that, the flower has a very long spur which contains the nectar, so only long-tongued bees can reach the nectar - barring nectar robbers which will make a hole in the spur. The wait was worth its while, as last week, later than I have seen this species before, a female Anthophora furcata turned up and fed on all available flowers, collecting the pollen. She was also pollinating the flower, you might see the flower's anther pushing against the bee's head. The bee came back again the same day for another visit. She had large bare patches on the abdomen and thorax, but still showed the characteristic fringe of red hairs at the end of the abdomen. The flowers are beautiful, it is a native plant and it attracts one of my favourite bees, what else can one ask for?

UPDATE 20/09/12
Since writing this post, I have watched the long tongued bumblebee Bombus pascuorum visiting these flowers too.

On insect migration and fairy tales

When it comes to invertebrates, very odd ideas can circulate even in scientific circles. One of such is called 'The Pied Piper' effect, and states that many insects migrating to northern latitudes in the spring do it hopelessly, as their offspring will be incapable of making the return trip to the region of origin, where they would be able to successfully overwinter: a one way migration trip. Of course this makes no evolutionary sense. If in a population some individuals were genetically predisposed to migrate north each spring - while the rest stayed put - and the offspring of such migrants had no chance to make the return trip successfully, natural selection would select against migratory behaviour: migrants will quickly be purged out of the population, while the offspring of sedentary individuals would be more successful and propagate their sedentary tendencies resulting in a non-migratory species.
  No matter how ridiculous this idea might seem to us, it has persisted for decades, in a similar way that Aristotle believed that swallows and other birds hibernated in the mud at the bottom of ponds or that Redstarts turned into Robins in the winter. An enormous body of research has confirmed that birds are capable of migrating back and forth to distant regions and have a magnetic compass that allows them to navigate even in adverse meteorological conditions. Bird migration is now widely accepted. Could it be that our prejudices with invertebrates made us find impossible to believe that some of them also could be able of regular back-and-forth seasonal migration? It appears so. But an online early paper by Jason Chapman and co-workers, from Rothamsted Research Station demonstrates that migration in an insect is an adaptive behaviour. Migrating insects use resources that are geographically and seasonally partitioned: in the summer they are available in more northern latitudes than in the winter and a two way migration is the most profitable way to use these resources. They collected data on the Silver Y, a common noctuid moth which is known to migrate from the Mediterranean to temperate latitudes in northern Europe. This species breeds continually in up to five generations a year and cannot survive the winters of northern Europe. The very active adults (above, adults often vibrate their wings when resting and when feeding) feed on nectar-rich plants and their caterpillars grow on a range of plants, including crops, where they can become a pest.
Building on a large body of previous work of the group on insect migration, some of it I already covered in BugBlog, these researchers analysed long term moth trap monitoring data at a national scale and entomological radar data. Both sets of data agree beautifully, complementing each other. The authors estimate that between 10 and 240 million Silver Y moths migrate annually to the UK, There strong inter annual variation in numbers and three years between 2000 and 2009 with exceptionally large immigration events in 2000, 2003 and 2006, likely due to benign ecological conditions in their wintering grounds. Their results provide solid evidence of the astounding population increases - and therefore potential reproductive benefits - experienced by migrating Silver Y moths in their northern breeding grounds. As the summer progresses, adult populations increase on average four-fold and for each moth that arrives in the spring, three will start the autumn return flight. There is a clear two-way movement: northern in the spring and southern in the autumn, with the autumn migration being of larger magnitude. But are they able to migrate all the way back? Simulations of expected moth return flights using flight and wind speeds and orientation of flying moths detected using the radar support the hypothesis that most of these moths could reach to their wintering grounds in the Mediterranean successfully. The Silver Y now joins the Painted Lady and the Monarch butterfly as models of insect migration, banning the 'Pied Piper effect' to the realm of fairy tales.

More information 
Chapman JW, Bell JR, Burgin LE, Reynolds DR, Pettersson LB, Hill JK, Bonsall MB, & Thomas JA (2012). Seasonal migration to high latitudes results in major reproductive benefits in an insect. Proceedings of the National Academy of Sciences of the United States of America PMID: 22927392

The Hornet mimic Large Alder Sawfly

One of my first posts at BugBlog dealt with a strange caterpillar I was unable to ID. The caterpillar turned out to be the larvae of a rare sawfly, Cimbex connatus. The following summer I came across an adult, but it was dead and squished, so I never blogged on it. Today, just coming out of work I spotted what I thought it was a hornet on the ground. I got very excited, as I have never seen one, but my excitement turned quickly into disappointment and then into more excitement when I realised that it was in fact an adult, alive - although on its last legs - Cimbex. This is an awesome European hornet mimic, down to the abdominal pattern, size and general colouration, including the wings, and general body shape. @RichardComont at Twitter identified it as Cimbex connatus, the large alder sawfly.

Sawflies are a large and heterogeneous group in the hymenoptera, the order that includes stinging insects such as bees ants and wasps, although sawflies are harmless. The family to which Cimbex belongs has characteristic clubbed antenna. Males have enlarged hind legs and mandibles - which apparently use to fight with other males for access to females. Females have a saw-like ovipositor. They lay their eggs on specific trees or bushes and their caterpillar-like larvae feed on the leaves and come to the soil to pupate. 

I believe my specimen to be a female, as she has got an enlarged abdomen with the ovipositor sheath being visible underneath it. It measures 21 mm. I mounted it on a piece of white tack to photograph it in a more life-like position.

A side view of Cimbex connatus

A front view reveals a fierce-looking face, with large, sharp jaws and clubbed antenna.

This species is one of three large Cymbex species found in the U.K. it was regarded as extremely rare if not extinct. According to Mark Boddington:

Following a half-century hiatus to 1997, we have recent records of Cimbex connatus (Schrank) from more than ten counties in southern through eastern England, reaching as far north as the Humber. Over much of this area, C. connatus is now comfortably the most frequently encountered member of the genus, followed by C. femoratus (L.) and C. luteus (L.), the latter species in particular being infrequently seen. 

The expansion of Cimbex connatus in the UK might be linked to the increasing use of Italian alder trees, Alnus cordata, and similar species to line avenues in towns and cities.

Cimbex connatus larva found under Italian alder (23/09/2008)

The very surreal caterpillar

Something was eating the young wisteria, but we couldn't spot the culprit, until today. A large, freshly moulted Vapourer Moth caterpillar, also known as Rusty Tussock moth, Orgyia antiqua. Their odd arrangement of hairs and tufts, with neat 'shaving brushes' on their back and tail, and four feathery tufts on a grey-black and red background make it look strange indeed. And if the caterpillar is strange, the adults no less so. Adult male Vapourers are pretty day flying moths, russet coloured with a white spot on each forewing and large feathery antennae. In contrast, females are large, slow moving and flightless as they only have vestigial wings. They don't move far from their cocoon during their short lives, commonly laying their eggs on the cocoon itself. The adults do not feed, but the caterpillars are generalist feeders and use a wide range of bushes, and compensate for their mothers immobility by dispersing widely. I have seen the caterpillars from June to August. After her white bowl treatment, this one was moved to the large cotoneaster, where I have seen them before.

More information
UK Moths page.

Migrant Common Darters

At this time of the year, my garden - which hasn't got a pond - hosts occasional dragonflies as they migrate to warmer climates. The most regular one is the Migrant Hawker, which often hunts in small parties 2-3 m high, occasionally stopping to rest hanging from branches. Rarer species are the Darters. In the last few days, I have watched female Common Darters, Sympetrum striolatum, resting and hunting. The first day it banked atop my parasol and I couldn't get good shots. Today I was luckier and the darter sat on the fence. With the help of my new Canon Powershot G12 flip out LCD display, and perched on a chair, I could hold the camera high enough to get its portrait.

This species, as other darters, is known to migrate regularly. David and Elizabeth Lack reported their pass south in the Pyrenees together with migratory birds, butterflies and hoverflies in October 1950 and reviewed the information available on dragonfly migration until then. Today, although the morning was warm with sunny spells, a large front with thunderstorms passed through all the afternoon, so it could be that the dragonflies were moving away from the coming rain. 

Common Darters are known to form occasional irruptive, massive migratory swarms, although the reason for these are not well known. A large irruptive swarm of this species was reported in Ireland in August and September 1947 by Cynthia Longfield from the British Museum. She compiled the letters of many observers amazed by the sudden, unprecedented invasion, including interviews with schoolchildren, which helped document the spatial extent of the invasion. As, she was visiting Ireland at the time, she identified the dragonflies and further documented the invasion with her observations. She concluded that this mass invasion event probably came from Spain and Portugal, as no invasion was reported in France or England at the time. She calculated that the dragonflies must have flown over the sea overnight. It is hard to imagine what being there at such massive influx event would have been:

'They were flying low in compact formation. . . . The flight was orderly, in a northern direction, as if they were intent on reaching some known destination.'
'They seemed more to be drifting with the breeze than flying, but were keeping to a straight course, without zigzagging or undulating, coming in from-the sea to the south and going north. What was so remarkable was the witnessing of the actual arrival and passing of the swarm.'

'They seemed to be coming in from the sea and flying about two feet above the ground, though some were higher, to about eight feet up. All were flying in the same direction, northwards. It seemed a never-ending stream, but we had to move on, and passed out of their track, so I could not tell the duration of the flight. They flew considerably faster than we were walking. The density was about one foot, or rather less, apart.'

For the next day, 3rd September, Mr. Allen writes: 'Tuesday's invasion was nothing to Wednesday. Wind south-west. Before noon they commenced and continued until evening. They not only came singly, drifting as on Tuesday, but in great, thick black masses, like dark clouds. They really frightened the people.'

Here he found 'the people looking out to sea, and I saw a sight which gave me a fright at first. I heard a hum like bees and yet not quite like bees. The next thing the whole sky filled with large flies that resembled aeroplanes, millions of them'

 Cynthia hypothesizes that the reason these dragonflies were emigrating was the drying up of the marshes where they regularly bred. That these dragonflies somehow were prevented from completing their reproductive cycle in the region of origin is illustrated by the fact that many of them paired on arrival, and some were even observed laying eggs on the sea. Although these spectacular irruptions appear to be extremely rare occurrences, they illustrate that the more regular, seasonal migratory behaviour of some dragonflies, can possibly be exacerbated by unusual weather conditions in their region of origin - in a similar way that occurs with Painted Lady irruption years.

More information

Cynthia Longfield (1948). A vast immigration of dragonflies into the South coast of Co. Cork The Irish Naturalists' Journal, 9 (6).
David and Elizabeth Lack (1951). Migration of Insects and Birds Through a Pyrenean Pass. Journal of Animal Ecology, 20, 63-67 DOI: 10.2307/1644