The Batman hoverfly

Surely, this is not an accepted English name for this common and widespread hoverfly, but the reason that this species is easy to identify is its distinctive 'Batman' logo on its thorax. This large female fed on the fennel with two other individuals. I find it amongst the most handsome of the British species. The larvae is of the rat-tailed maggot type, like its relatives, Eristalis, the droneflies and Helophilus (the 'Footballer hoverfly') and it typically breeds in rot holes in trees where leaves decompose.

Drama under the barbeque

This morning, while watching the hoverflies feeding on the fennel I realised I wasn't the only one interested in them. A female digger wasp Ectemnius, was poised on a cherry leaf, attentively following the action, and at one point the spotted a suitable hoverfly victim and attempted a capture.
 In the afternoon I came across Ectemnius again. Another female inspecting potential nest holes in a bee hotel, going in and out of them.

 I decided to sit and watch the action, faintly hoping the wasp would start digging a nest. I noticed the characteristic carded silk threads of Amaurobius spiders (top shot), and thought that spiders and digger wasps must come across each other with some frequency as female wasps inspect nesting sites. Then the wasp moved to the log pile under the BBQ and walked in and out amongst the logs. She appeared to have walked onto a silk thread and a false widow spider, Steatoda bipunctata, promptly came out of her refuge. A fight ensued, the wasp trying to bite or sting the spider, the spider spreading silk on the wasp and retreating, and repeating the procedure as the wasp became more and more entangled and buzzed intermitently in her futile attempts to get herself free.

 
The commotion got an Amaurobius out of her retreat, and at some point both spiders were attacking the wasp, although the Steatoda managed to secure it and, when the wasp stopped fighting, the spider cut free the threads that attached the prey to the log, and pull her to the safety of the retreat.

Early stages of the fight

The Amaurobius' legs are visible behind the abdomen of the wasp in the shot above, while the Steatoda secures the jaws of the wasp with more threads of silk

The wasp front end is now tightly wrapped on silk, now the spider focuses on the rear end

The spider drags the wasp to her retreat

 I watched all this with amazement and struggled to get decent photos as the action happened almost behind the log. The whole sequence of events happened within 15 minutes!

Candy-stripe spider

 I found four Candy-stripe spider, Enoplognatha ovata, females guarding their lovely blue egg sacs under the lid of my garden waste bin. The spiders have probably been transferred to the bin with branches cut from some bushes, and had moved with their egg sacs to the drier lid. This one floated down from a thread of silk, and I brought it home to take her portrait on the white bowl. Another thread of silk attached the female to its egg sac, as can be seen on the following side shot:

Although these are small spiders, about half a cm long excluding the legs, they are powerful hunters, and they are able to subdue wasps, honeybees and even the aggressive Wool Carder bees, which they capture on their loose, disorganised web under flowers or leaves, where the females guard their egg sac:

Enoplognatha with its male Wool Carder Bee prey

this one with wasp

with Episyrphus balteatus hoverfly

This one hiding underneath a Feverfew flower got a honeybee

This spider shows a striking color polymorphism, which is genetically determined in a complex way. I have found the three colour forms in my garden. The abdomen can be plain pale yellow (variety lineata, top shot), yellow with two dorsolateral pink stripes (var. redimita):

or yellow with the dorsal surface of the abdomen entirely pink (var. ovata), the rarest in my garden:

In addition to the colour polymorphism the presence and number of black spots is also variable, as it can bee seen in the above photos. This species also occur on both coasts of the USA, presumably introduced from Europe. In the UK, there is a very similar species, also colour polymorphic, E. latimana, which has been recorded mostly in the south of England and it appears to be less common than E. ovata.

Flies dancing on water

Approach a pond in July or August and crouch down. Focus on the surface of the water, checking the floating leaves or debris by the water edge and you will likely see jittery, shiny green flies. Get comfortable and watch them for a while, it takes some time until you can transport yourself to this small, alien world. These are long-legged flies, Poecilobothrus nobilitatus. They like to rest on floating objects or the mud on the edge (above), but they are also able to walk on the water surface. You will notice that some flies, the most active ones, have smoky wings with bright white wing tips - they are the males (top shot). Clusters of males may dance around single females, which lack the white wing marks (below).

Female walking on the water surface

To start courtship, the male focus on a female and approaches her, then he opens his wings in straight angles to his body and buzzes them quickly before closing them again, the wing-waving display, which is just a component of their complex and spectacular courtship. 

 Here several males circle a female wing waving, although the wings are barely visible as they are buzzing them. The three males court a female, which is watching the male in the right.

A male in the middle of wing waving

I took a little clip of their courtship earlier today.

The details of the courtship are a combination of wing waving and aerial acrobatics too fast for the human eye to follow, but they were described in detail by M.F. Land, which examined an hour of videos of courting flies in a pond in Sussex. The following figure from his paper represents the longest bout of filmed courtship, which was interrupted by the male chasing another male. Wing waving upon approach to a female is followed by hovering in front of her and flying over the female and back, and more wing waving. Courtship is often interrupted by chases to other males and then returns to the same female to carry on.

(from Land, 1993)

UPDATE: Thank you to Morgan Jackson for pointing out that this fly was one of the species in the Name a Species 2012 competition and won the lovely English name of Semaphore fly.

More information

Land, M.F. (1993). The visual control of courtship behaviour in the fly Poecilobothrus nobilitatus J Comp Physiol A, 173, 595-503 DOI: 10.1007/BF00197767

Spotty Eyed Hoverfly

Occasionally, I wonder if this blog can be long lasting, given the subject is my garden invertebrates. Can I regularly find something worth writing about without repeating myself? These doubts, however, are always short-lived, as I am time and time again surprised by a new species or by regular ones behaving in ways I haven't observed before. This afternoon, before the skies opened and rain started falling after a couple of dry weeks, I watched hoverflies, always plentiful this time of year. The flowering fennel and yarrow, both with flat umbels and many small flowers with easy to reach nectar were buzzing with them. A small, stout hoverfly fed on the fennel. I didn't recognise it and I was amazed by its unusual spotted eyes. Taking photos was tricky, as the slender fennel stems swayed on the wind. I took many, and discarded most, but these are the best I managed.
 The wonderful Garden Safari website helped to identify the species as Eristalinus sepulchralis. Unfortunately, despite having browsed Stubbs and Falk, the plate in which it is pictured is at the same scale than other much larger droneflies, and the characteristic eyes were not apparent in the small drawing. Also, as the drawings are based on pinned specimens, and eye colour fades on dead specimens the contrast between the yellow background and the darker spots is lost. This species is characterised not only by its unusual eyes, but also for the striped thorax, metallic bronze sides of the abdomen. Despite it being my first sighting, this is a common and widespread species, with maggots of the rat-tailed type that develop in wet areas. Adults overwinter and feed on a range of flowers.