Friday, 30 July 2010

A business of hoverflies

A business and a swarm, are the collective terms for flies, in this case, hoverflies. In the last few days, hoverflies, particularly the Marmalade fly, Episyrphus balteatus (above) have descended covering every flower, bush and branch with a stripy fuzziness. The group of Marmalade hoverflies on the flowering teasel above greeted me first thing in the morning. As I have said before, many hoverflies are migrants: numbers are swelled in the summer by migrants from southern Europe. I have taken shots of several species today, including Scaeva pyrastri, which I had only seen once in 2006 before, and now seems to be everywhere.
Syritta pipiens on fennel
Eristalis sp.
Syrphus sp.
Scaeva pyrastri on Knapweed
Myathropa florea on fennel
More information
Stubbs A.E. & Falk, S.J. (2002) British Hoverflies. BENHS.
Hoverfly Recording Scheme.

Wednesday, 28 July 2010

Clouds of Horse-Chestnut Miner

The Horse Chestnut Miner (Cameraria ohridella) is a tiny, 5 mm moth whose larvae feed in the inside of Horse Chestnut leaves. This tree is native from the Balkans and it is there, on Macedonia, where the moth was first found in the late seventies and later described as a new species, although it is not thought to be native from Europe. From there the moth has spread to the rest of Europe, wherever Horse Chestnuts are cultivated. The first infestation in the UK found in 2002 in Wimbledon and since it is steadily spreading North and now reached Scotland. The mining larvae cause chararteristic brown blotches on the tree leaves, which grow in length but are restricted to the space between main veins. Damage differs quite a bit between trees, but even those quite affected by the miner seem to recover the next season and the miner does not seem to transmit any tree illnesses.
A typical blotch in close-up and...
...a larvae extracted from its leaf
Lightly affected leaves on the first of July
Heavy infestation on mid july
A heavily infested tree
A few specks on leaves of a lightly infested tree.
Yesterday morning and today I passed underneath a heavily infested horse chestnut. There was a cloud of miner moths flying about, then stopping briefly on a cotoneaster underneath. Both days, the moths were not as obvious in the afternoon. I wonder if they form mating swarms, although I haven't found any information on it, despite many years of research into the mating pheromone and ways to control them.
There is currently a survey on to follow the moth spread across the UK and monitor the levels of infestation and the level of natural control by parasitoids. It is very easy to enter data about your local conker trees and the website is here.

Tuesday, 27 July 2010

Queen ant makes spider dinner

I have come across queen garden ants (Lasius niger) for a week. The first one, a wingless one wandering on the garden checking every little crack on the cement eager to start digging her nest. She was quick and the light conditions weren't ideal, so, reluctantly, I moved her to a white bowl for a portrait (above). Yesterday, queens and males were emerging en masses from nests on the side of the street pavements in the afternoon, ready to start their nuptial flights.
The males are similar in size to workers, the queens, double their size and with a much larger abdomen.
Male garden ant
 I even got a mating pair, with the female dragging the male about and both flying away:
Mating ants (the male's antenna can be seen on the right hand side of the queen)
The queen ants will usually mate once in this flight and then land and dig their nests and live underground the rest of their long lives, the males will die shortly after. I say the queens, but I should have said the lucky queens. Most of them will actually die before they hit the ground again, eaten by swifts, swallows, gulls or sparrows. Others will contribute to a spider bonanza. Hundreds of aphids and some ants could be seen yesterday and today covering the webs of the missing sector spider (Zygiella x-notata) on railings. One queen wandered on my conservatory wall and fell on the disorganised cobweb of a Steatoda bipunctata spider, who quickly approached the ant (maybe biting it?) and retreated to the corner of its web. A few minutes later the queen had stopped struggling, and the spider came out for his dinner.
Steatoda bipunctata with dinner
The spider drags the queen ant to its retreat (notice the screw head for scale).

Monday, 26 July 2010

More on Wool Carder Bees

Mating Wool Carder bees on Lambs ears, note the larger size of the male.
As I do with other bees, I have been recording the flowers the Wool Carder Bee visits and today I have compiled the results. As expected, the bee is most strongly associated with Lambs' Ears (43% of 89 records) on which the female collects hairs and both sexes feed and the male eagerly patrols; one in four of records is associated to Lavender (25%) and one in ten in Sage. Foxgloves make almost 5% of the remaining records. The rest of the species comprise 16% of the records and include Jerusalem sage (Phlomis), French Lavender (L. stoechas), Verbena bonairensis, Hedge Woundwort (Stachys sylvatica), Geranium, Sedum, Caryopteris, Purple toadflax (Linaria purpurea) and Lemon balm (Melissa officinalis). Of course, this is biased to the plants I grow in my garden, and I have reason to believe that other plants - or the minority plants - are favourites of this bee (for example Purple Toadflax and Stachys sylvatica, for which my observations are casual records in other places near home).
This photo tries to show a typical male patrolling behaviour: he is hovering for a few seconds in front of a Stachys flower spike in search of females and intruders, then moving to the next spike and darting to the lavender patch he is also guarding. A male yesterday patrolling Lavender attacked in a few minutes Episyrphus balteatus, Bombus terrestris, Apis mellifera, and Megachile centuncularis, all of which were feeding on the lavender I also compiled the phenology of this species in Hull from my records and this is the occurrence graph, by fortnight and separate for males and females.

Finally, a couple of days ago, I took a photo of an unusual bee feeding on Buddleia. Stuart Roberts identified it for me in Wild about Britain as Stelis punctulatissima, the rare cuckoo be of the Wool Carder Bee. Most recods of this bee are from localities where the Wool Carder Bee is frequent. The photo is below.

Sunday, 18 July 2010

Harvestmen season

I have seen quite a number of harvestmen - also known as daddy long legs - in the last couple of weeks, and realised I hadn't posted on them yet. At a distance harvestmen look like skinny, long-legged spiders, but a close-up look reveals they are not spiders (see above a female possibly of Opilio canestrini). Harvestmen belong to the order Opiliones, within the class Arachnida, and they are related to mites, spiders and scorpions and so they have eight legs. They can be distinguished by their fused body, as opposed to the cephalothorax and abdomen of spiders, and more similar in looks to that of scorpions -but without the tail. They have two eyes close together on top of their body, on a tubercle, unlike spiders which have eight eyes. Their legs are very long, and the first pair is even thinner and longer and acts like antennae, constantly sensing the ground like a blindman's stick. They also have a pair of pedipalps and chelicers. Unlike spiders, harvestmen produce no silk, have no venom and are generalist feeders. They have two forms of defence: if trapped they emit a foul-smelling substance which acts as a deterrent to predators. They also shed their legs easily and the severed leg carries on moving for a while, which allows them to scape while the potential predator is distracted with the moving leg. One of the harvestmen I saw yesterday (below, possibly female Phalangium opilio) had only one leg on one side of the body: it wasn't the most elegant walker, but it managed to move quickly enough.
Another important difference from spiders is that harvestmen actually copulate, as males have an intromitent organ. This drawing, from Hillyard and Sankeys' monograph, shows the larger female and the male facing each other 'in copula'.

More information
Harvestmen: keys and notes for the identification of the species.1974 By P. D. Hillyard, John H. P. Sankey. Here.

Monday, 12 July 2010

Maternal behaviour in Tegenaria

ResearchBlogging.orgOn top of a log pile under a shelf in the garden lives a large female Tegenaria. She has a large funnel shaped sheet web with a deep retreat. Every time I water the plants nearby - something I've had to do a few times in the last few weeks due to the dry weather - she jumps out of her retreat to the front to the web, only to find that there is no prey, just some water dropplets, and then she rapidly hides again. Today, I got my camera on one hand and a watering can on the other and managed to get a few close ups of the spider, which dutifully posed for me for quite a long time after being prompted by the watering. I also photographed her funnel and when I looked closely into the photo I could clearly see two tiny spiders on it.
The female Tegenaria at the front of the web
Two spiderlings at the top of the funnel (click on the image for full resolution)

Many female spiders display maternal behaviour, the most basic version consists on wrapping their egg clutches in a silky cocoon which protects the eggs from predation and adverse environmental conditions and shelters the spiderlings during their first moult. Some spiders go further than that, for example wolf spiders carry their egg sacs and spiderlings on their abdomen for a while. Tegenaria - the usual bath spider - has a different kind of maternal behaviour: the females, usually agressive and predacious towards prey entering the web, in contrast 'accept' the spiderlings on their webs for about three weeks after hatching, often longer, until these disperse. The tolerance behaviour turns into cannibalism as the spiderlings grow, but by then most of her offspring would have dispersed. Mated females lay several egg clutches in the spring - the offspring of the previous autumn males.

Females in all reproductive states - even virgin females - tolerate newborn spiderlings on their sheets, but females which are at the reproductive state when they have spiderlings are the most tolerant of all. Females rapidly approach foreign spiderlings placed on their webs but after touching them with their first legs and palps leave them alone, while they often attack and eat crickets of the same weight. The female's behavioural changes towards older spiderlings have probably to do with chemical changes in the spiderlings cuticles. Even if it seems like a very simple form of maternal behaviour, the fact that the spiderlings are able to remain on their mothers web for a few weeks is likely to dramatically reduce their chances to fall prey to predators.

More information
Pourie, G., and Trabalon, M. (1999). Agonistic behaviour of female Tegenaria atrica in the presence of different aged spiderlings Physiological Entomology, 24 (2), 143-149 DOI: 10.1046/j.1365-3032.1999.00124.x

Friday, 2 July 2010

Spider on a white background

This tiny bright-green spider (Araniella sp.) is usually wonderfully camouflaged amongst the bushes and low vegetation where it spins its web. This female, however, is laying in wait, with open arms atop a cluster of white Philadelphus flowers and was easy to spot at a distance. There is some debris from her meals at the bottom of the photo below, revealing that small flies and aphids flying past form part of her diet.
 The following photo is a dorsal view of a female of the same species.

Cinnabar moths and caterpillars

ResearchBlogging.orgDuring a walk in my local wildlife garden we noticed the first Cinnabar Moth (Tyria jacobaeae) caterpillars of the year, and an adult also flew by. The caterpillars clustered at the flower heads of Ragwort (Senecio jacobaea), which they prefer as food, and had defoliated the plants quite a bit. Many had already left in search for greener pastures and were around the ground or wandering over other plants. Cinnabar Moth caterpillars have a strong tendency to cluster together, an antipredator behaviour.
This behaviour , however, gradually dissapears as the larvae grow so that fully grown fifth instar larvae are actually agressive to each other and tend to be found spaced out in the plants.
Adults emerge in late spring from overwintering pupae and after mating, female lay eggs in the basal leaves of ragworts. Larvae hatch in about two weeks and their development takes about one month, after this, they pupate on the ground and remain in diapause until the following spring.
This moth is often active by day and therefore easy to spot due to its contrasting coloration, but they are most active at dawn and dusk. When they fly, their pink hindwings are quite apparent and they can be taken for some exotic bright pink butterfly. The bright colours of the moth and particularly, the striking yellow and black stripy pattern of the larvae are a warning sign of their distastefulness to vertebrate predators, a phenomenon called aposematism. The larvae ingests and stores in its tissues toxic alkaloids from the foodplant and the adult also synthesizes additional toxins itself. Surprisingly, many invertebrate predators feed on eggs and caterpillars of this moth.
Given that Ragwort is a toxic plant for horses and has been introduced in several countries where it has become an invasive weed, a lot of effort has been directed to study the ecology of the Cinnabar Moth as a way of controlling Ragwort.

More information
J.P. Dempster (1982). The Ecology of the Cinnabar Moth, Tyria jacobaeae L. (Lepidoptera: Arctiidae) Advances in Ecological Research, 12, 1-36 DOI: 10.1016/S0065-2504(08)60076-8