The sun appeared shyly behind the clouds after a shower. It is milder than in the last few days today and I wandered out in the garden to try and get some shots of the Winter Gnats (Trichoceridae). These are dipterans which are active on the winter months. Males gather in swarms from a few to dozens of individuals in assembly points over prominent bushes or trees and fly bobbing up and down. If you can get close to the swarm they might take you as their 'assembly point' and dance over your head. Occasionally each individual alights on the bushes. That's how I got the still shot of one.
Females enter the swarm to chose a male and mate.
Other than the Winter Gnats there was little active buglife in the garden. Three 7 Spot Ladybirds are hibernating in between the leaves of the Monkey Puzzle.
Some individual garden spiders, familiarly installed in strategic spots in the garden have disappeared in the last weeks, probably after laying their eggs and spinning a cocoon around them in a safe, dry corner. I came across this magnificent female, going on a walkabout. The largests I've seen (a 1 p coin for comparison).
It has been a very mild Autumn so far. Today, temperatures rose over 15 oC. A butterfly fluttered over my head. I thought it could be a Red Admiral. Fortunately, it settled to sunbathe on a white, south facing wall, and using my camera telephoto I was able to take a picture and identify it as a Peacock. It is the latest active Peacock I have seen since I started to record butterflies in 2003.
This is the usual phenology of Peacocks in my grid square (TA0830). A single brooded species, adults break hibernation in April, breed, and the next generation is on the wing in July. Butterflies usually start hibernation in early September.
After their slow start this year, Harlequins are around with a vengeance. There are some railings near my local park literally covered on larvae, pupae and adults, presumably all need to emerge as adults before the winter sets. When my daughter came running to show me a ladybird I though it would be another harlequin. But it was instead a very nice surprise: an Eyed Ladybird, Anatis ocellata, the largest ladybird in the UK. This species is associated to conifers and there are not many in the park so it appeared a bit misplaced.
Suddenly, most of the summer bugs seem to have disappeared to leave your usual autumn suspects: wasps, a few Bombus pascuorum, garden spiders and plenty of flies. There is a common bug, though, that hangs on year round. It is the window frame spider, Zygiella x-notata. This species is an orb spider (related to the Garden Spider, Araneus diadematus) which spins its webs on gates, window frames, wheelie bins and other flat surfaces associated to human constructions. The web is quite recognisable, as it has a sector with no connecting threads in it, it is thought to be adapted to be built in such flat dimensions by keeping the signal thread free from getting tangled in the sticky connecting threads. The signal thread runs in the middle of this sector and allows the spider to detect any vibrations due to insects trapped in it. During the day, the spider hides in a silky tube on a corner, with the first pair of legs touching the signal thread that leads to its web. At night she is often seen either just outside the retreat or on the web, in a more similar way to garden spiders.
A Zygiella x-notata web on a garden gate. The spider's retreat is on the top right-hand corner. Note the signal thread and the 'empty' segment on the orb
This one used to live inside the kitchen window.
Eventually, she laid her eggs and spun a cocoon for them. She sat on the cocoon until she died.
It's that time of year again. Come early autumn, large, long-legged, fast spiders take you by surprise crawling across the living room, or alongside skirting boards or, better still, greeting you when you are getting in the bath - where they have fallen the previous night. They are house spiders from the genus Tegenaria. It is not a large genus, with only 11 species in Northern Europe, but they include the largest spider in the UK, the Cardinal spider Tegenaria parietina, which can reach 14 cm across its legs (see the proof here). Tegenaria are remarkably difficult to identify to species level, something I find quite frustrating. Forget about it with the females (unless you capture them and closely examine their genitalia). Even with relatively close shots of male palps identification is difficult. You have to content yourself with Tegenaria sp. Females usually keep to their web on hidden, dusty corners around houses or under beds. The wandering house spiders of the autumn are actually males in search of females.
This one stayed on a skirting board for a whole day a few days ago.
I got a close shot of the palps of this other male, three years ago to the day.
A couple of weeks ago I did the usual annual compilation for 2009. I have compiled my butterflies records and submitted them to the local Butterfly Conservation recorder since 2003. It has been a super butterfly year. I recorded a total of 17 sp. within the boundaries of the City of Hull. One of the most noticeable species this year has been the Small Tortoiseshell. This Small Tortoiseshell was the first butterfly I saw this year, after the long, cold winter, sunbathing on the pavement on a busy street.
There has been a lot of talk about the population decrease in this species, possibly due to mortality due a newly arrived parasitoid tachinic fly, Sturmia bella. This fly has been found to parasitise up to 40% of south England Small Tortoiseshell caterpillar clusters. There seem to be additional reasons, as this butterfly shows marked cyclic population fluctuations even before the fly was recorded in the UK.
The graph above shows the collated results extracted from the UK Butterfly Monitoring Scheme 2007 report (well worth browsing if you like butterflies).
Despite all this, 2009 has been the best Small Tortoiseshell year since I record butterflies.
This is my total year count graph, showing the 'rebound' of the Small Tortortoiseshell after the 2006 'low'.
This is the phenology of this species in Hull.
It seems likely that there are two broods a year.
I discovered a great butterfly site, packed with info and with superb photos: learnaboutbutterflies.com
I was walking home through the University woodland area in the afternoon when a large flying insect called my attention, a moth with bright pink hindwings and an erratic flight. It took a while to settle, and it did so on a tree trunk. When I got close I could not see it. I had spotted it when it had landed, so I took a few shots of the trunk, where was it? Can you see it?
and then I saw it. Thanks to it hindwings being slightly exposed.
It was a Red Underwing (Catocala nupta), a large noctuid which flies in August and September, and whose caterpillars feed on poplar and willow. It seems to be a rare species in the North, but it seems to be expanding in range. In the NBN gateway it does not even appear in Hull.
I moved to writing my nature diary on the computer a year ago. I started using Evernote, for a series of reasons (a recent entry above). It is free, accessible from many platforms and it also has the ability to synchronise notes and you always have an updated back-up copy on the web. Importantly, it is fully searchable and you can put photos or websites in it, in this respect it is quite flexible. The main problem with it, for the use I give it, is that I cannot export the notes in other format than text, and even then, the note creation date does not appear in the text file. I have partially avoided this by writing the date on each note, but is a bit of an extra effort. I also would like it to have a system in which I can do a search for a species and then be able to export the search as a tab-delimited text which I can import into Excel, say, in order to submit my records to various recording societies. Also, I wish I could draw on the notes! I love the feeling when going through my old notebooks looking for something (when did I see the first butterfly this year?) that is missing in the electronic form, devoid of little drawings and sketches - a bird carrying a stick, a sunbathing butterfly, a bee - which give it personality and conveys a sense of the moment. I'd love to hear if anybody records electronically and what software they use.
A sketch on a sunbathing Red Admiral on a fig leaf (14th September 2006).
I went for a walk the other day to the local Wildlife Garden. I was taking photos of autumn berries and when I went to see how the acorns were doing I couldn't find a single intact one. The handful of oaks in the hedge were covered in all sorts of galls on leaves, stems, buds and acorns. Some galls are quite attractive, others just plain bizarre. These galls are produced by the larvae of tiny gallwasps (Cynipidae). These wasps are one of the few a very group of organisms (with waterfleas, rotifers and aphids) that alternate in their mode or reproduction between a sexual phase (with male and females, usually in spring) and an asexual phase (females which reproduce parthenogenetically usually in the summer). Both reproductive phases often happen in the same oak species, but in some cases they occur in two different ones. The gall is a response of the tree tissues to the presence of the wasp larvae and the shape of the gall differs depending of the species of wasp. The gall offers protection and food to the growing larvae, which after pupation, emerge as adults through a hole. There are over 30 gall wasp species in britain in the common oak alone. Despite their tiny size, gallwasps have their own parasitoid species, also wasps!
All the galls in the photos are produced by the summer, asexual generation on the pendunculate, or common oak, Quercus robur.
Marble Galls, produced by the larvae of Andricus kollari. The exit hole is visible in the middle. The sexual generation uses the Turkey Oak, Q. cerris. This wasp species was introduced in the 19th century and is now widespread.
Knopper Galls on acorns. Produced by Andricus quercuscalicis. Adults emerge in spring to produce the new sexual generation on catkins of Q. cerris (a non-native oak). They first appeared in the UK in 1960 and they are now widespread. I think the little wasp at the left of the centre of the photo is the gall wasp.
Common Spangle Galls produced by Neuroterus quercusbaccarum. The sexual generation forms Currant Galls in young leaves and catkins.
Silk Button Spangle Galls produced by Neuroterus numismalis. The sexual generation causes minute galls on leaves in spring.
Artichoke Galls produced by Andricus fecundator which lays eggs on terminal or leaf buds.
One night of early July, a large female hawkmoth heavily laden with eggs got in our laboratory through an open window, attracted by lights. Before she died, she laid her eggs on the window glass.
It was lucky somebody noticed the dead moth and eggs and kept an eye on them. Tiny pale green caterpillars with disproportionately large heads, started to emerge on the 27th of July, and proceeded to eat their egg shells.
After a quick internet search we identified the hawkmoth as a Poplar Hawkmoth, Laothoe populi, one of the commonest in the UK. After bringing in some poplar branches, the caterpillars started munching away and growing, and growing. After four weeks they were full size, beautiful velvety green caterpillars with yellow and red markings.
Nineteen of them have now pupated and I'll keep you posted when/if they emerge some time next May.
A butterfly day: Small Tortoiseshells, Red Admirals and Painted Ladies sunbathing in the morning and gorging on the buddleia blooms; Speckled Wood in their never ending spiral flights. Same old same old. I witnessed more dramatic things though. A Small Tortoiseshell left the spot on the ground where it was sunbathing and flew straight onto the middle of a large garden spider web. The spider quickly grabbed it from below, while the butterfly frantically fluttered trying to get away. The fight continued for a minute or so, then the butterfly started to flutter more and more slowly until it gave up. I didn't have my camera with me (I though I did but it was only the case, doh!) so I returned later and tried to find it. Here it is, the full spider holding onto its neat small tortoiseshell meal or the remains of it.
As I was leaving the spider, two common blues, a female with a male closely following her, fluttered by my head. I watched. They looked like they wanted to settle, flying low amongst the bushes, and after a bit they did, on some marjoram. They rapidly took positions facing away from each other, closed their wings and mated.
I had completely forgotten I had put the parasitised ladybird (see previous post) on a plastic container to see if the parasite wasp emerged and to be able to take some photos. I checked regularly the first few days and nothing happened. Today, sixteen days later, I came across the container and there was a tiny wasp, flying about! The ladybird was still alive and it could now move its front and middle legs. I managed some shots of the pair together.
The wasp returned to the ladybird again and again, inspecting it with its antennae. I released the wasp in the garden and it settled nearby so I could take one final shot before it flew away.
For a week I have been watching hawker dragonflies hunting over the garden well into the evening. They fly high (3-5 m) and never seem to stop, so I could not identify them. My luck changed today, when early in the morning I came across a male Migrant Hawker (Aeshna mixta) sunbathing on a fence outside. This is the only species of hawker I have identified in my garden and I usually see it in August and September. It is quite approachable and getting close-ups is relatively easy.
The male was a little later joined by another individual (a duller male I think) and both sunbathed quite close to each other high up in a buddleia for a while.
My usual basic photographic equipment was joined by a chair, so that I could take the pictures. At 11:30 both dragonflies started hunting and they didn't stop again.
This species of dragonfly is very sociable and regularly hunts in groups. Is also, as suggested by its name, a regular migrant species. Before the 1950' it was quite a rare species in the south of the UK but steadily increased its range and is now found also in S. Scotland and Ireland.
It seems like a good year for 7 spot ladybirds. There are many more these days than Harlequins around here. Some ladybirds I see are parasitized. I dug on the web today after taking a few photos of one and noticing the ladybird was actually alive, moving its head and palps, but unable to walk. The indication that it was parasitized was the presence of a silk cocoon underneath it to which it seemed to be tethered. The parasite is a tiny braconid wasp, Dinocampus coccinellae apparently a parthenogenetic species. Shortly after emergence, the wasp lays eggs inside larvae, pupae and adult ladybirds. The larvae hatching from this egg starts by eating the reproductive organs and eggs inside the ladybird, causing little external damage, then it develops a trophic organ that absorbs nutrients from the ladybird. The cycle becomes even more gruesome from now on. When the larvae is ready to pupate it severs the ladybird's leg nerves, by which it becomes paralyzed partially paralises the ladybird through some chemicals. The larvae then emerges from the ladybird through a hole she bores and spins a cocoon between the ladybird's body and the substrate (leaf, twig, etc). The ladybird is alive but paralysed and the parasite pupae enjoys the protection of the ladybird aposematic colors until its emergence a week or so later through the pointy end of the cocoon. Although some ladybirds recover from the parasitism, most presumably die, and it is not known if the survivors will be able to feed and reproduce after this ordeal!
More info and photos here. To be continued here.
Butterflies have high predation rates by birds. I am sure most of you have come across a butterfly with damaged wings suggestive of a beak 'bite' mark. Long-lived butterfly species often rely on camouflage (crypsis) to avoid being attacked in the first place. The Comma, the Small Tortoiseshell and the Peacock are some of these, mimicking shriveled leaves. They remain immobile if resting, with their wings closed. The Peacock (Inachis io) has a second defense mechanism. If discovered, they suddenly flash their wings open, exposing four large eyespots they also may flick their wings repeatedly and at the same time they make a hissing noise and a series of inaudible clicks by rubbing two wing veins together, during this display, they continually adjust the tilt of their bodies to face the potential attacker.
This Peacock was feeding upside down on a Buddleia showing its eyespots
This intimidating display was described over a century ago and its effect on predators noted, but experimental support for its effects on the survival of the butterflies themselves was lacking until very recently. Adrian Vallin and collaborators tested the effect of eyespots, stridulation and both combined by modifying captive-reared peacock butterflies experimentally. They removed the eyespots by painting over them with a black marker pen and removed the stridulation ability of the butterflies by cutting out the veins responsible for making the hissing noise. They also tested the effect of the combined factors, that is removing both the eyespots and the noise-making wing veins. Unmodified controls, and controls in which a similar area of wing was painted black without touching the eyespots or cut without affecting the ability to make noise were also tested (bottom row below).
The researchers recorded the effect these various treatments had on survival of peacocks upon exposure to a potential predator, blue tits (Cyanistes caeruleus), a small insectivorous bird. The results show conclusively that butterflies without eyespots are more likely to be predated by the blue tits. All except one butterfly with intact eyespots survived by scaring the blue tit away, showing how effective the eyespots are in intimidating the bird. The effects of the sound or the combined effect were not significant. The predated butterflies were readily eaten by the birds, indicating that the Peacock is not distasteful and supporting the view that, in the words of the researchers, 'a harmless prey can increase its fitness by survival through the adoption of intimidation by bluffing'.
References: Vallin, A., S. Jakobsson, J. Lind & C. Wiklund (2005) Prey survival by predator intimidation: an experimental study of peacock butterfly defence against blue tits. Proc. R. Soc. B. 272:1203-1207.
Yesterday I came across some piece of fascinating research on the silver Y (Autographagamma), 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