Playing catch-up

The unexpectedly long period of warm weather in April brought everything on very quickly, so we're having what I can only describe as an early and 'strong' spring and early summer. I'm already seeing species that I would not expect until the end of May or start of June, and the Orange Tip butterflies have already laid their eggs:

Orange-Tip butterfly egg

The female lays a single egg (the larvae are cannibals) at the rear of the flower where the seedpod will form. The larva will feed on the seedpods as its sole food until it pupates.

The males are already sedate enough to stop for a photograph: normally they are far too flighty most of the way through May.

Male Orange Tip butterfly

Towards the end of the season - probably around 3 weeks' time - females run out of empty flowers and 'dump' their eggs on plants which already have eggs (or even larvae) in situ. These are doomed to be eaten, but the desperate females rely on the remote chance that their eggs will survive. This shows the importance of synchronisation with the sole foodplant: too early and there will be nowhere to lay; too late and all the suitable flowers will already be occupied.

Fungal rusts are also wasting no time:

Uromyces dactylidis on Creeping Buttercup

In common with most other rusts, Uromyces dactylidis requires an alternate host to live on while the primary vegetation is missing. In this case it's a range of grasses. I always find it intriguing that alternate hosts are rarely closely related to the primary host.

I'm currently working with a number of schools in the Heritage in Schools programme run by the Heritage Council in Ireland. This enables schools to book visits by heritage experts at a lower price than they would normally pay. I'm covering Natural Heritage, and this shot was taken at a visit to a school last week:

Common Frog

During a six-week period, we will count the species in a number of local habitats and draw up a biodiversity map for the local area. This will enable us to determine factors that encourage or inhibit biodiversity.

One early species found last week was the bumblebee-mimicking hoverfly Eristalis intricarius. During the early years of my local survey, this species confined to one small local area, but in recent years I have found it in more and more locations. It must be finding something that is beneficial.

The bumblebee-mimicking hoverfly Eristalis intricarius

Serendipity

My photography sessions are dominated mostly by the weather, and even when the weather is half-reasonable I can still struggle to get half a dozen decent shots. Sometimes, however, everything clicks and I manage to get a good range of illustrative images.

Scaeva pyrastri is a hoverfly that can be readily identified by the abdominal markings: they are paler than most species and the inner part of the curve is further forward than the outer part. In this shot, you can also see the hairy eyes, which separate it from other similar species.

Scaeva pyrastri hoverfly

Scaeva pyrastri is thought to be immigrant from mainland Europe, and I know that there has been a mass migration of moths to Ireland in the past couple of days, so this hoverfly has almost certainly flown from France to breed here. (The brown hoverfly at top left is Eristalis pertinax).

Eristalis intricarius is one of our best bumblebee-mimicking hoverflies:

The bumblebee mimicking hoverfly Eristalis intricarius

That yellow/orange 'band' is very convincing in life, but when you see it close-up, it's clearly just a scutellum with longer than usual hairs.

And just as I was standing up from taking that shot, I saw the very bumblebee that it is mimicking:

Bombus lucorum (agg) (right) and Bombus pascuorum (left, both workers)

That's a nice shot of two of my 6 local bumblebee species.

Helophilus pendulus is perhaps the most common single species of hoverfly on the patch at the moment. I know that there are a few related (but rarer) species that might be around, so I examine each specimen very carefully just in case. Today I got that 'eureka' moment as I found this male Helophilus hybridus:

Helophilus hybridus (male)

Helophilus hybridus larvae are associated with black mud where Bulrush is present, and the adults don't disperse very far. There is a stand of Bulrush about 300m. from where this shot was taken.

Here's an archive shot of Helophilus pendulus for comparison:

Helophilus pendulus (archive)

Notice that the yellow abdominal markings are quite different, and the rear legs are yellow only at the 'knee' in hybridus, but the yellow is extensive on pendulus.

The larvae of some fly and micromoth species feed on the seeds of composite flowers such as Knapweed. The seeds are an excellent food source, and the larvae can feed inside the undeveloped seedheads in relative safety.

Notice the word 'relative'; some parasitic wasps are aware that there are larvae inside the flowerhead, and at the appropriate time (now) we can see the Ichneumonids searching the unopened flowerheads. When a larva is detected, the ovipositor is deployed and we see the drilling operation that takes place:

Ichneumonid ovipositing in larvae inside the Knapweed flowerhead

The eggs are deposited inside the body of the hidden larva and will remain there until the larva has reached full size. At this time (or soon after the larva has pupated) the ichneumonid egg hatches out and the ichneumonid larva eats the host before pupating inside the husk. This egg-laying process can be seen in perhaps three days per year.

Here's an unusual shot of the process from the rear:

Ichneumonid ovipositing

A few days ago, I showed a picture of a very atypical Square-spot Rustic. Here's one that looks as if it has read the book and followed the rules:

Square-spot Rustic

Here's a link to the original post, for comparison.

Early year?

I'm hearing many reports of species being 'early' this year. Species have been appearing at earlier and earlier dates over the past few years; so much so that it has almost become the accepted norm and people don't even mention it any more. But this year I'm again noticing that more people are making special mention of early specimens of moths, butterflies and other insects, so perhaps things are particularly early this year.

The following shot certainly illustrates that trend as far as I'm concerned, but before I discuss it, what type of insect do you think the following picture shows? (bumblebee, wasp, fly, other?):

Male Eristalis intricarius

Well, to put you out of your misery, it's a hoverfly: a male Eristalis intricarius. These are good bumblebee mimics, and at first glance, when they're stationary, they are easily mistaken for Bombus lucorum.

A few identification pointers might help. Firstly, it has only two wings; flies have two wings, bees have four. Secondly, the head is almost completely made up of eyes. In a bee, the eyes are long and narrow, with visible parts of the 'face' on both sides of the eyes. (Incidentally, the fact that the eyes meet in the middle is what makes it so clearly a male). Thirdly, what appears to be an orange stripe between the wings is actually the shiny scutellum, and isn't really a stripe at all. Finally, if you look carefully at the wing veins, you can clearly see the famous 'Eristalis bulge', which is unique to the Eristalis group of hoverflies:

Eristalis 'bulge'

The shot also illustrates another of the wing features which identify hoverflies: the 'False margin':

The trailing edge of the wing is not constrained by a vein: it is free to flex as the wing moves. I rather suspect this is one of the main reasons why a hoverfly can hover so accurately.

In terms of earliness, I have only once seen Eristalis intricarius before June: I have come to regard it as a summer species. The references say from March, but that would probably be a date from much further south.

The next shot shows a couple of tiny flies (on Dandelion for scale). On the left is a Sepsid fly: these run around on leaves and flowers with their wings flapping up and down in a semaphore fashion. On the right is one of our smallest hoverflies, Neoascia podagrica:

Sepsid (L) and Neoascia podagrica (R)

Here's a close-up of the (8mm. long, female) hoverfly:

This is again much earlier than I would normally expect to see it.

In terms of grasses, the first to flower around here is usually Sweet Vernal Grass, but that hasn't appeared yet.  Instead, I found Meadow Foxtail:

Meadow Foxtail

I have included a little insert (top left) showing the very short 'ligule' which can be used to assist with identification.

Tiny gap in the rain

It had rained for 48 hours and I spotted a small gap in the cloud, so I drove the two miles to this part of the hedgerow (Leg 2) as fast as I could. By the time I arrived it was raining again.

Five minutes later.....

I glimpsed this insect half-hidden under a leaf. What do you think it is? (the major - and huge - clue is clearly shown).



Not Bumblebee, but a Bumblebee mimic, the hoverfly Eristalis intricarius:

Notice how the scutellum (the orange bit) is wide and hairy, giving the appearance of a golden band, like a bumblebee. The clue in the first image is the obvious 'loop' in the wing veins....the 'eristalis bulge'.

This is a close-up of the face, showing the tiny antennae and the three ocelli or minor eyes between the main eyes. Many flies, bees and wasps have these extra eyes which are very sensitive to light change, and are used to detect movement.

A rolled leaf is like a magnet to me, and I reckoned this was the home of a micromoth larva. (You can see the ejected frass (dung) to the left of the image).


Sure enough, a little poking and prodding revealed the larva of the Timothy Tortrix micromoth. Notice the areas of buttercup leaf that have been consumed.


This micromoth larva is gravely at risk. Within half a metre of the larva I found two potential predators. First the so-called flower bug, Anthocoris nemorum (about 4 mm long). These are predators of moth, butterfly and sawfly larvae.

And also this wonderful, minute (3 mm.) Ichneumonid. These parasitic wasps also target larvae.


The rain had barely stopped for a minute when three male Orange Tips appeared from under the edge of the ditch. No time to waste when the ladies are expected to be out and about.

Mimicry and more

Here's a close-up of the Bumblebee Bombus cryptarum:


Bombus lucorum was recently split into 3 species: Bombus lucorum, Bombus cryptarum and Bombus magnus. Bombus cryptarum was added to the Irish list in 2006, and consistent sampling has shown that my local population contains this species. I recently posted about the Cuckoo Bumblebee Bombus bohemicus, which was known to be parasitic on B. lucorum sensu lato, but I don't know if it also parasitises B. cryptarum or if I also have B. lucorum s-s, which I rather suspect. Work to be done, here.

The best diagnostic feature of B. cryptarum is the black notch in the forward yellow band, just in front of the wing joint:

Just as the parasite B. bohemicus is a lucorum lookalike, we also have the hoverfly Eristalis intricarius:



Note the distinctive Eristalis loop in the wing vein.

There are two main reasons for the mimicry. In the case of parasitic species like the Cuckoo Bumblebee, it may need to be able to get into the nest undetected, so it looks rather like the host. In the case of the hoverfly, it can either be to get into the nest undetected, or to fool predators into thinking that it is a Bumblebee, and can sting. Eristalis intricarius larvae live in the bottom of ditches, so they are applying the mimicry to avoid being eaten by birds.

Eristalis intricarius is known to be widespread, but in low numbers, and of the 50 or so specimens I have found over the past four years, they can all be pinned down to two separate patches of ditch, each no more than 10 metres long. So there is something that controls their distribution very tightly. To make things even more confusing, the two ditches (roughly 1.5 km apart) could hardly be less similar:

One runs North-South, the other East-West. One is at the edge of cattle pasture; the other, the fringe of a bog. One is fringed by Meadowsweet, the other Soft Rush. Just about the only thing in common is some Hawthorn and some Gorse and Bramble. Interesting......