Marmalade flies everywhere!

Marmalade flies, Episyrphus balteatus, are the most common British hoverfly, and can be seen year round as they are able to overwinter as adults. However, at this time of the year, they are at their most abundant, as I walk around the garden, every flowers seems to have a few males hovering nearby or females feeding on the flowers. These slim, small hoverfly is able to migrate, and this occasionally bumps the numbers of British individuals. They are very distinctive, as the pattern of double black lines in the abdomen is unique to this species. The male above (eyes meet at the top of the head in many male hoverflies), settled briefly on an Agapanthus flower bud, and rubbed its feet together, keeping its wing open for a few seconds.

Bright batman hoverfly

Here, a female Myathropa florea basks on a leaf over the wildife garden pond, which is now almost dry. Although batman hoverfly is not its common name, the distinctive batman symbol on this fly thorax makes it very distinctive. This hoverfly has a very long breeding season and you can see it from April until November, where it is often seen feeding on Ivy flowers. Individuals may vary in their brightness and this is because those that develop at high temperatures are brighter (like the one above) than those growing at colder conditions. This is a very common, opportunistic hoverfly which breeds in rot holes in trees or other hollows with wet rotting vegetable matter, where their 'rat-tailed' maggot larvae develop.

More information
Stuart Ball & Roger Morris 2015 Britain's Hoverflies: A field guide. 2nd ed. Wild Guides.

Insects at the University Woodland Area

This afternoon, I joined James Gilbert and Robert Jaques to search for hoverflies, bees and other insects in the woodland area at the University grounds. It was overcast and mild, and a surprising number of insects on the wing. A few Hogweed umbels were a big attractions, as were the buttercups (a handsome Helophilus pendulus above).

The Batman hoverfly, Myathropa florea on hagwort

Nettle tap moth

A male Bombus lucorum swinging from the flowers.

This is a dronefly, Eristalis pertinax.

There were at least three male longhorn, Nemophora degeerella, moths about. They danced as they flew high up. It looks like quite a challenge to fly with such oversized antennae, which presumably attracts the female's attention. This one rested on nettles for a while.

A female Marmalade fly, Episyrphus balteatus, with extended ovipositor.

And to finish, a Speckled Wood. I rarely see these butterflies nectaring. They have a short tongue and like to lap honeydew on tree tops, but the exposed, flat flowers of the hogweed seem to appeal to them.

Insects in flight

Today it was a summery, hot day, with a light breeze, ideal for insect watching. Somehow, I managed a few decent in flight shots, which usually evade me as I am not patient enough. The first one happened when I spotted two hovering Volucella pellucens. They are large hoverflies, which live near trees and are identifiable even at several meters of distance due to their translucent abdominal belt. Males hover incessantly on the same spot, and inspect or chase off other hoverflies and even speckled woods invading their territory, so maybe this way they spot female hoverflies to mate. Hoverflies also hover during courtship. I tried to encourage them to sit on my finger by slowly raising it towards the hoverfly. This technique often works with hovering males, like this Eristalis intricarius from yesterday shows:

but the Volucella refused several times...

So I tried to get some shots while it hovered and got the shot at the top of the post, and I was pretty pleased with that!
 A bit later, then, in my street, a couple of migrant hawkers were hunting over the verges. Migrant hawkers often hunt together with other individuals, and they may settle to bask near each other. They tend to hunt from 4-5 m above ground. I managed some records shots, this one the best.

I popped in the wildlife garden later to release a grasshopper (a matter for a different post) and watched a large Ectemnius digger wasp (probably the common E. cavifrons) inspecting a rotten log. She had to fend off a Tegenaria spider. Ectemnius are hoverfly hunters and are skilful hovers. Females dig their nests in soft wood, and look by suitable nest sites, often hovering in front of the wood. This allowed me an opportunity for the third flight shot for the day.

Pied hoverfly

At the higth of summer, I occasionally see this stunning hoverfly, the easy to recognise Scaeva pyrastri. I am going to follow NatureSpot and others and use a common name, Pied Hoverfly, although swift hoverfly would be equally fitting to this migrant, quick flier. It is that time of the year when each flower in the garden is being visited by hoverflies, and the flowering fennel is attracting quite a few.

A new hornet-mimic hoverfly

 I found this large, colourful hoverfly feeding on Yarrow (Achilea millefolium) in the garden this evening. It is a male Volucella inanis, a hornet mimic which is also found in nests of wasps and hornets, where its larvae develop. Spot on, its numbers peak at the beginning of August. The entry in Stubbs and Falk's British Hoverflies notes that its distribution range is expanding north, and being the first time I come across this species, I checked the NBN Gateway: no records for East Yorkshire or anywhere north of the Humber. Another species expanding its range due to climate change? I should start keeping a list.

UPDATE 4/08/2013. Barry Warrington e-mailed me with some more info about the species in East Yorskshire: "V. inanis is scarce in our County. I recently found one a couple of weeks back and having liaised with the YNU Diptera recorder and checked the Watsonian Checklist, my find was the first for East Yorkshire. It is clearly spreading well and quickly, with it being most common in VC63."

A Pellucid Hoverfly

This is the striking, and relatively common hoverfly, Volucella pellucens. Yesterday afternoon I watched this female feeding on dogwood blossom. It is a very large fly, mostly black, with a translucent, pale first abdominal segment. Males are very obvious this time of year, as they hover, a few meters high, near trees. Even in flight, their colour pattern and size makes them easy to identify. They live in woodland and park glades, although I have also seen it a few times in my garden.
The adults feed on umbellifers, buddleia and bramble flowers, amongst others. An interesting aspect of this hoverfly life cycle, although still relatively poorly known, is that its larvae are found inside the nests of social bees and wasps. Adult hoverflies are apparently able to enter unnoticed the well guarded nests, and lay their eggs in the nest. The larvae feed at the bottom of the nest, scavenging on dead adult bees or wasps or grubs, pollen and dropped food and other debris. In the autumn, when the nest is vacated, the larvae might move into the combs, when they finish off any late grubs.

More information
Stubbs, A. E., & Falk, S. J. (1983). British hoverflies. An illustrated identification guide. British Entomological and Natural History Society.

Elder aphid networks

The photo above shows a dense colony of Elder aphids, Aphis sambuci, many individuals of different ages feeding close together. They are likely to be all a clone, female descendants of a single founding female that emerged from an egg early in spring, and identical genetic copies of her. Elder aphids forms this characteristic ash grey patches on tender elder stems. The aphids suck the elder sap using their piercing mouthparts. Having a close look at elder aphids gives you an opportunity to learn to learn about ecological networks in a few minutes of observation. All the photos in this post were taken in the space of seven minutes this morning on my way to work on the same young elder bush.

 Despite the fact that elder, Sambucus nigra, has relatively few insect predators, most likely due to it having cyanogenic chemicals in its leaves, elder aphids are an important link in networks making use of elder sap. 

Ants have a mutualistic relationship with the aphids. They benefit from the aphids honeydew by soliciting them to excrete it, taping them with their antennae. The sugary rich liquid is consumed by the ants and their larvae. The ants treat the aphids as their domestic animals. The aphids benefit too, as potential predators or parasites are pursued or attacked by the ants.

But the ants can't totally defend the aphids from their numerous predators. Here a female hoverfly, Epistrophe eligans, lays eggs on a patch of elder aphids.

A hoverfly egg is visible on the centre of this photo, on the edge of the aphid colony.

See the patches cleared of aphids in this patch? They are due to predation by the green hoverfly larvae just visible amongst them. Surrounded by food, the larvae will gorge on the aphids and grow rapidly.

This hoverfly larvae (possibly Epistrophe eligans) is likely to be ready to pupate.

Not only hoverflies, ladybirds are attracted by this aphid bonanza and adults land on the elder, possibly attracted by the smell of aphids. A Harlequin sunnies itself on a leaf...

...while an active 2 spot searches about.

Ladybirds have laid their bright yellow egg clutches on or under the leaves, near the aphid colonies.

...here visible on the background. I couldn't find any ladybird larvae today on this elder. 

This fly enjoyed licking the honeydew on a leaf. Some species of butterflies, like the Speckled Wood, also takes advantage of honeydew.

Five species (2 ladybirds, a fly, an ant and a hoverfly) thriving on elder aphids. If I had waited a bit longer, or being a bit luckier, I could have witnessed tiny parasitoid wasps that lay their eggs inside the aphids and eat them from the inside!

Egg laying Footballer hoverfly

Footballer hoverflies are commonly seen near water: ditches, ponds and drains, their genus name Helophilus, actually means 'lover of marshes' in Greek. On a little twig over a puddle on the pavement by a busy road, two Helophilus pendulus females - their abdomens large and turgid with eggs - laid. While one of them was busy actually laying under the twig, the other seemed to be 'feeling' the twig with the ovipositor, probably selecting the best site to lay her shiny white eggs. Note the ovipositor stretched out. Helophilus lay their eggs on clumps - like bluebottles - unlike other hoveflies which lay individual eggs singly. This might well be due to their different feeding habits. Many hoverfly larvae are predatory, and being born away from hungry siblings might give them a better chance to find food (like aphids). Helophilus are related to Droneflies, and their larvae, called rat-tailed maggots, are aquatic, and develop on very wet manure or submerged rotting organic material often in large numbers, so they are less likely to compete for food. Their 'tails' are actually long telescopic breathing tubes, that they can retract into their bodies.

 For a great series of shots of Helophilus egg laying and larvae development check BugGuide.

Another shot of the laying female

I turned the twig to reveal the egg clutch after the female lad left. As they lay under the twig, the eggs are not readily visible.

Loving the ivy

The late flowers of the ivy are a bug magnet in the autumn, when other sources of nectar are scarce. I have posted before on ivy fest season, but today I came across some new ivy visitors in a large ivy just starting to bloom in my local cemetery. Speckled Wood butterflies rarely visit flowers, as they usually feed on honeydew produced by aphids up in trees. So, I was pleasantly surprised to see two individuals feeding on ivy together with a Comma and many Droneflies.

Speckled Wood and Comma

Comma

Dronefly Eristalis tenax

Male wasp

Helophilus

Yellow dung fly?

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.

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.

A beautiful wasp-mimic hoverfly

While in the wildlife garden a couple of days ago, I noticed a large boldly marked hoverfly male hovering by the pond. I managed just a couple of shots, but this one is enough to identify it as Chrysotoxum festivum, a relatively scarce hoverfly in the north of England. Unlike other hoverflies, this genus has long, forward-pointing antennae, which contribute to liken it to a wasp. There is little information on the biology of this genus, although the larvae have been found inside ants nests, where they presumably feed on ant-attended ground aphids. 

The Footballer hoverfly

From mid April up to October, you might come across this handsome hoverfly resting on leaves or feeding on flowers either close or away from water. This species is Helophilus pendulus, the commonest of its genus in the UK, distinguished by other species by the parallel yellow stripes in the thorax, black stripe on its face and the mainly yellow hind tibia. The genus Helophilus, which is a wasp mimic, is closely related to Eristalis, the droneflies, which are bee mimics. Both genera share a rat-tailed aquatic or semiaquatic larvae. I found this female sitting on a sage leaf after a light shower. She was cold and reluctant to fly, and with a bit of coaching, she climbed on the white bowl and let me take her portrait.

On the odd life cycle of bumblebees

I stopped by the comfrey patch this morning. The comfrey has now been in blossom for a good month. A Small White butterfly was feeding on comfrey, but I couldn't snap her. A ginger queen Bombus pascuorum fed on the blossom. A queen wasp got comfortable on a leaf and basked in the sun, as did some hoverflies. While I watched a couple of Anthophora plumipes males patrolling and feeding, a tiny worker of the tree bumblebee Bombus hypnorum, the first of the year, turned up (above). As I compared the sizes of these two bees – the bumblebee worker was smaller than A. plumipes - I reflected on the different life cycles of these two bee species. A. plumipes, a solitary bee, has males and females, while bumblebees, in addition of males and females (queens), have a worker caste. In bumblebees there are no males for most of the year: A male has a relatively short - if hectic - life. Upon emergence in the summer, he will find a queen and mate with her. The queen will store his sperm and use it to fertilise her eggs the following spring, when she will emerge from overwintering, build a nest and lay fertilised eggs, which will hatch into worker larvae. She will be busy collecting nectar and pollen from early flowering trees and plants to rear these larvae, and once the workers emerge, they will take over from the queen in collecting more nectar and pollen for subsequent eggs, although they won't reproduce themselves.  In the summer, the last batch of eggs of the queen will produce new queens and males, which the workers will help rear. Once they leave the nest, the founder queen and workers will die and the cycle starts again. Wasps, ants, bees, and bumblebees (hymenopterans) share a weird way to determine the sex of the offspring: fertilised eggs become females and unfertilised eggs become males: a system called haplodiploidy.

  Most sexual organisms have two sets of chromosomes: a set they inherit from their mother and another that comes from their father, but as bumblebees and other hymenopterans do not have a dad they just have a single set of chromosomes, the set coming from their mother.

How strange is that? If you think about it, the system means that bumblebee males don’t have dads, they also cannot have sons, only daughters, although they can have grandsons and have granddads. In addition, this arrangement causes strange relationships between the family members. We are equally related to our parents than to our kids – on average – but due to haplodiploidy, bumblebee sisters are more strongly related than they are to their mums. This is because full sisters have received an identical set of chromosomes from their dad, in addition to the set they receive from their mum, which is a mixture from the sets the queen received from her parents.

 This unbalanced genetic relationship between mother-daughters and sisters is thought to underlay the evolution of the worker caste, which do not reproduce, but help their mother to rear their own sisters.

The solitary bee Anthophora plumipes

A wasp? No, the exquisite wasp mimic hoverfly Myothropa florea

This is the real wasp. A queen common wasp 

Hoverfly Syrphus ribesii 

Another basking fly

A queen Bombus pascuorum