Having mentioned in my last post that St. Marks Flies (Bibio sp.) are out, I got this shot of a male this morning:

St. Mark's Fly - Bibio marci (male)

We can tell it's a male by the large eyes, which meet in the middle. In Bibios, like many other flies, the male has much larger eyes than the female, and often emerges earlier in order to establish his territory. Bibo larvae are root-feeders on many plants, especially grasses. St Mark's day is 25th April, and the flies get their name from the fact that they usually emerge around that date. I've been seeing them for about a week, so the year is still rather early. Bibios are large flies that fly around in large groups - almost swarms - often with their rear legs hanging downwards.

When I was checking the images, I noticed that I had a decent shot of a couple of interesting features:

Bibio marci head (close-up)

Firstly, we can see how hairy the eyes are. Interestingly enough, the hairs don't interfere with the fly's vision: an insect's compound eyes are made up of tubes with sensors at the inner end and a lens at the outer end. These lenses are all arranged on a curved surface, which makes them all point in slightly different directions, which is good for all-round vision. The hairs grow parallel to the tubes, and as a result have minimal impact on the vision, since the line of sight is along the hairs, not across them. These large eyes are used for navigation and for identification of mates, prey and food.

Secondly, we can see the triangle of three ocelli (auxiliary eyes, arrowed) which react very quickly to changes in light intensity, and are used to detect quick motion in order to avoid predators.

A few years ago I took a series of 'bug's-eye' views of plants. Here's a view of a Dandelion seed clock from an unusual perspective:

Dandelion seedhead

 I rather like that shot.

A few of our hoverflies have grey abdominal bands rather than the usual yellow. This is a female Platycheirus albimanus feeding on Dandelion:

Platycheirus albimanus (female)

This is by far the most common species of hoverfly in my garden at the moment.

Drumboe insects

Drumboe has a very rich insect population: I find some of my most interesting species here. This is Nomada leucophthalma, which is parasitic on the mining bee Andrena clarkiella. This is yet another prime example of dependency timing: A. clarkiella uses only the pollen of willows to feed its young, and willow pollen is only available for perhaps 6 weeks of the year. So the Nomada must locate an available Andrena nest and lay its own eggs there in a very short timeframe. Nomada sp. are known as kleptoparasites: they use the pollen the Andrenas have collected for their own offspring.


This specimen was flying along the vertical earth bank looking for Andrena nests. They fly facing the bank and move sideways as they search. This behaviour can be seen for only 4 weeks of the year. Shot was manual focus!



This is an Andrena, but not the one parasitised by the above Nomada. Andrena haemorrhoa, about 15 mm long:



Smaller hoverflies are making an appearance at last. This is a male Melanostoma scalare:


The larger Eristalis pertinax has been around for a couple of weeks. This is a female:



A single Speckled Wood was the first of the year for me. I also saw one Orange tip male and a Green-veined White, both of which I showed the other day.


St. Marks Flies are so-called because they usually start to appear around St. Marks day - April 25th. They're usually pretty accurate.


I have never found a convincing identification for this one, but it should be Bibio marci.