Sawflies

Sawflies (Symphyta) are a very understudied group of insects. They belong to the Hymenoptera, which includes Wasps, Bees and Ants, but the female has a saw instead of a sting, hence the common name. The saw is used to cut slots in leaves, and she then lays her eggs into the slots as an anchor to hold them in place, often laying many eggs on a single leaf. The larvae look very much like the caterpillars of moths and butterflies, but they have more prolegs and are generally more tapered, with wider 'shoulders' and narrower rear ends. They also have very simple ocelli on the larger eyes, only a single dot rather than multiple dots as found on moth larvae.

Larva of Arge gracilicornis

The eggs are laid on particular plants, sometimes a single species of plant, but often within a closely-related family of plants. Some species are leaf miners and some others make galls, although the majority of larvae are free-ranging.

I'm not quite sure why Sawflies are so studiously ignored by many entomologists. True, there are many species and many are very similar to each other, often requiring a specimen and a microscope to identify accurately, but other groups are like this, so I'm not quite sure why they are seen as 'difficult'. I suppose it must be a lack of literature: there is very little out there: the main key (Benson in 3 volumes) is now over 60 years old, but I have found the key to be no more difficult than other groups such as beetles or flies. One difficulty is the larvae: they go through a series of moults (instars) as they grow, and can vary their colour pattern quite substantially when they do so. So in order to identify the larvae we need to know all the variations for each species. Cameron's four-volume monograph, written in the late 19th century, includes coloured drawings of some larvae. A further difficulty is that we don't yet have a full knowledge of which larvae turn into which adults. With moths and butterflies, the match is more or less complete, since a great deal of work has been done with them and they are relatively easy to breed through in captivity, but with sawflies the life cycle can sometimes be a bit more complex, and many attempts to raise them in controlled conditions have failed. So we have a situation where some larvae are as yet unidentified, and the larvae of some of the adults are unknown. Clearly, much work needs to be done here.

Adult sawflies can be difficult to distinguish from other groups, but they always have a thick waist like bees, rather than a narrow one like wasps. The thorax is often strongly sculptured.

Tenthredopsis nassata

 

Tenthredo livida, male

Larvae often adopt a tail-up stance when disturbed. The movement is quite sudden, and I have seen parasitoids being propelled through the air if they approach too closely. This is the larva of Nematus pavidus, which is a common Willow feeder:

Larva of Nematus pavidus

The differences between species are often microscopic, and we need to examine a specimen under magnification. With some species we need to see further details, such as the shape of the teeth on the saw. This is the (2 mm,) saw of a Tenthredo:

Saw of a female Tenthredo sp. Sawfly

A few years ago I studied a series of colonies of Nematus pavidus on my local Willow and it is documented here.

Sawflies certainly need attention, and I intend to focus on them this year.

A couple of surveys

I was invited to help with a couple of surveys this week and found some interesting specimens. The first location was a disused mill with associated ponds, dams, millraces and reservoirs. This is a wonderful site covering tens of acres, with old deciduous woodland and various meadows in addition to the water features mentioned above. It was also on limestone, which I always find interesting. Sedge and grass specialists would have a field day here. We were actually hoping for butterflies, but it was dull and wet, so I concentrated on leafmines, which are always there despite the weather.

First interesting specimen was this one on Ground Elder:

Blotch mine on Ground Elder

Most mines are specific to family, perhaps even species of plant, but this is the mine of Phytomyza angelicastri, which is more usually found on Angelica. So this isn't a new mine for me, but it is a new host for that species. I can now add that insect to plant association in my Donegal Wildlife database.

There were a couple of specimens of Early Marsh Orchid in the middle of a path next to one of the ponds:

Early Marsh Orchid

Sawflies are one of the least-studied groups of insects. They are difficult to identify to species, often requiring dissection for a certain identification. The larvae are also poorly documented, and since they can change their appearance dramatically when they shed their skin, identifications are very tricky. One or two species can be identified from photographs, but first you have to eliminate similar-looking Ichneumonids. This is the sawfly Tenthredo livida (male):

The sawfly Tenthredo livida (male)

One of the main characters that can be used to separate Ichneumonids and Sawflies is the microsculpture on the thorax. In this case, it looks like the letter 'M':

Close-up showing microsculpture on the thorax

Ichneumonids tend to have a smoother thorax, although that's not a hard and fast rule.

This Eristalis hoverfly caused me a few id problems.

Eristalis nemorum  (male)

One of the main keying features for these is the facial stripe, which is more or less absent on this specimen. So that immediately keys to Eristalis arbustorum. But this didn't look right for that species. The key caters for specimens of E. arbustorum with a slight facial stripe caused by wear and tear, but this still didn't key out properly until I took into account the very narrow stigma (dark thin line) on the outside edge of the wing. This is a feature of Eristalis nemorum, which I am now told can sometimes be found with no facial stripe. I suspect that some of this variation is caused by the fact that my local specimens are found on acid soil, but this specimen was on lime.

Caddis flies are always found near water, since the larvae live at the bottom of ponds, ditches, etc.

Caddis Fly

Shield Bugs, in common with all other Heteroptera, go through a series of nymph stages before becoming adult. In each stage they become slightly more like the adult in size and pattern. This appears to be a final-instar (full-size, with larger wing-cases) nymph of Pentatoma rufipes:

Final instar nymph of the shieldbug Pentatoma rufipes

 There was a family of Mute Swans on one of the mill ponds:

Mute Swan and cygnets

I wouldn't normally go near swans with cygnets, but I was advised that this pair were calm enough. The male quickly got between me and the family and hissed a bit, but stayed to the side, watching me until he saw that I was just taking photographs. Interestingly enough, this is new to my species list.

All in all a lovely location that I will revisit in the future.

A dry day!

Today was the first dry day since 28th April, so I wasted no time.

The Orange Tip larva continues to graze on the Cardamine seedpods:

Orange Tip larva on Lady's Smock

The micromoth in the next image is the first of two new species for me on today's page. It's Coleophora albicosta, which feeds on Gorse, spinning up inside the flowers and then, eventually, a seedpod.

The micromoth Coleophora albicosta

I like the configuration that Coleophora specimens have....very elegant.

The 6mm micromoth Elachista apicipunctella is a leaf-miner on a number of grasses:

The micromoth Elachista apicipunctella

Moth Flies, or Owl Midges have the most amazing hairy wings. The drag must be immense for such a small (4-5 mm wingspan) creature:

Owl Midge

I thought this close-up of the Banded Snail Cepaea hortensis was worth showing:

Banded Snail Cepaea hortensis

Because of the incessant rain, I missed the very start of the local orchid season. Some specimens of Northern Marsh Orchid already have open flowers:

Northern Marsh Orchid Dactylorhiza purpurella

With all the wet weather we've had, it's no surprise that the fungal rusts are so prominent. Puccinia urticata is specific to Nettle, and can cause these swellings on leaves and stems:

Nettle rust Puccinia urticata 

Fungi are quite expert at manipulating the shape of plants for their own benefit; in this case to maximise the surface area for spore production and dispersal.

Athous haemorroidalis is one of the Click Beetles. Click Beetles have a mechanism (clearly shown in the picture below) whereby they can trap and release a notch on their pronotum with a sudden click and go flying up in the air to right themselves if they get stuck on their back.

Click Beetle Athous haemorroidalis

An identification that has been bothering me for perhaps 8 years has finally been resolved. The Sawfly below is a male Tenthredo livida, which can be distinguished from other Tenthredo species that have white-banded antennae by the two-tone (pale v-shaped) stigma on the wings. You can just make out the red abdomen which identifies it as a male:

Sawfly Tenthredo livida (male)

As larvae, Tenthredo livida eat a wide range of plants, but the most likely candidate in this location is Raspberry. Now that I know what it is, I can check back on Sawfly larvae that I have previously photographed on Raspberry and check them for a match. I like tying up these connections, even if they take 8 years to resolve.

St. Marks Flies continue to appear through the year, and it's now time for Bibio pomacaeus, which is readily identified by the red legs:

St. Mark's fly Bibio pomonae

(The leaf it's resting on belongs to another Northern Marsh Orchid.)

Flies belonging to the Empidae are sometimes known as Dance Flies because they gather in swarms and move up and down in the air as they fly around each other. This is Empis stercorea, which spends its time between dances by catching other insects and sucking out their body fluids with that long proboscis:

Snipe Fly Empis stercorea

Agromyza nana mines Red Clover leaves, and the single larva can be seen right in the centre of the leaf.

Leaf miner Agromyza nana on Red Clover

I think I have a new favourite picture, but I rather suspect I'll get a new favourite, soon.