Yellow dung fly

This male Yellow dung fly, Scathophaga stercoraria, as the sole occupant of a very wet cowpat after a rain shower. Yellow dung flies are sexually dimorphic, males and females differ in size and colour: males are much larger and brighter yellow than the female. Larger males are better competitors, better to defend a bit of cowpat from other males. Males spend much of their time on the cow pat, while females only come to the cowpat to mate and lay eggs. Dung flies actually feed on other flies and insects attracted to the dung, but also on pollen and nectar and the dung itself, while the larvae will develop on the dung. Although of Yellow Dung flies are associated to large animal dung, especially cow pats, I've had them in the garden before, where they might have been attracted to compost.

A pair of mate guarding dung flies in the garden, 26/08/2006, illustrating their sexual dimorphism.

Semaphore flies

After a wildlife-packed June with the 30 days wild challenge, I felt like I needed a new focus and I decided to carry on a wildlife challenge by blogging/tweeting about an invertebrate I've seen that day for July. Yesterday, while walking by the local park pond I saw a Speckled Wood. The butterfly flew away, but it made me notice the flies dancing on the Colt's Foot leaves: they were Semaphore Flies, Poecilobothrus nobilitatus, a whole swarm of them signalling to each other. Although small, this species is very easy to identify by their smoky wings with a white tip. They are very active in July on muddy puddles and ponds.

Crab spider stalking fly

I spotted this crab spider in my local wildlife garden, it had this strange clock-work movement and grabbed my attention. Then I spotted the fly. The crab spider, a female Xysticus cristatus, legs outstretched, on the left of the photo. The large fly is on the right, having fed or drank from the base of a teasel leaf. If you want to know what happened next see this video.

A bee fly in the garden

I have always wanted to see a Bee Fly (Bombylius major). Yesterday I had a glimpse of one in the garden, but being unable to get a photo I later thought that I had mistaken a bee for one of them. Today, early in the morning, probably the same one came to bask on the wall, flying amongst two Anthophora plumipes males, and I had my camera with me. The bright white background wasn't ideal, but I was happy enough to get a few shots. Bee flies are bee mimics, with furry brown bodies of about 12 mm long and their proboscis is almost as long as their bodies and they carry it sticking out forward while they fly or at rest. They are very good flyers and feed while hovering. Males and females feed on nectar, but females also need to feed on pollen to produce eggs. Their long proboscis, which is also adapted for sucking and it is quite movable, allows them to exploit flowers with deep corolla tubes, such as primroses, Aquileguia, lungwort, grape hyacinths and wallflowers, and they are important pollinators of them. I wonder if the abundance of these flowers in my garden, which I grow to attract A. plumipes, has been a factor in attracting the Bee Fly to the garden.
 Bee Fly larva are ectoparasites of ground-nesting bees, (the genus Andrena, Halictus, Lasioglossum and Colletes have been reported). Bee Fly females lay their eggs dropping them in or nearby the tunnels of bees, even on flowers if the female can't find suitable nests. When the larvae hatch they either find the nest and go into an open cell, or latch themselves to a passing bee when they hatch on flowers.

The Bee Fly about to land

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

Crane Fly halteres

This Crane Fly or Daddy Long Legs (possibly Tipula scripta) got into the house and I gave a try to getting its portrait on a white background. It is pleasantly surprising how many insects that I expect to fly away immediately do actually stay still through my white bowl session. The little knobbed structures sticking out at the sides of the body are the halteres, typical of all flies but more prominent in these large flies. They evolved from the hindwings and when in flight move in opposite directions as the wings and are involved in balancing and steering and contribute to the exquisite flying abilities in the group, although crane flies themselves are weak, wobbly fliers