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.

Mixed bag

These are the last photographs from my usual stretch of hedgerow for several months. The day after I took these, the hedge was cut down to the ground to a distance of a metre from the road on each side for 200 metres. So there won't be anything worth posting from there until next spring. I don't know why the hedgecutter chose this totally inappropriate (and illegal!) time to do the cutting ("it's only weeds and bugs"), but we have to live with these decisions. Unfortunately, the wildlife can't.

Last year I showed a photograph of the capsid bug Lygus rugulipennis. This is its nymph from exactly the same area:

Nymph of  the capsid bug Lygus rugulipennis

If you follow the link back to the original picture, notice how different the adult is from the nymph. This is typical in bugs, and makes identification of nymphs that bit more difficult, since it's normally the adults that are shown.

Udea lutealis is one of the larger micromoths, and is to be seen on practically every verge and hedgerow at the moment. The faint pattern diminishes as the moth gets older, and mature specimens (i.e. a few days old) appear to be a uniform cream in colour:

The micromoth Udea lutealis

I spotted this larva of the Sawfly Arge gracilicornis on Bramble. I had hoped to follow its progress for a few days, but that is no longer possible:

Larva of the Sawfly Arge gracilicornis

I should also mention at this point that I will be unable to continue my 5 year study of the sawfly Nematus pavidus this year, since the Willows were also threshed to ground level and won't have leaves until next year. I hope I can find some more specimens elsewhere.

The fungal rust Puccinia graminis infects many different grasses. This infection is on a stem of False Oat grass:

Fungal rust Puccinia graminis on False Oat grass

I haven't seen very many specimens of the wasp-mimicking hoverfly Sericomyia silentis this year. This one was on Male Fern on the other side of a deep ditch:

Hoverfly Sericomyia silentis

Earwigs are universally despised and, I think, a bit unfairly. They are quite unusual in that they tend to stay in family groups, whereas most other insects abandon their eggs/larvae. This is a male (the pincers are curved) Forficula auricularia:

The earwig Forficula auricularia

This one was photographed in my garden: I found it when checking a pot full of Fuchsia cuttings. Notice how small the wing covers (the squarish area next to the middle leg) are. Earwigs can actually fly, but I rather suspect that they are reluctant to do so because the wings have to be folded around 40 times to get them into such a tiny space.

New identification.

Update

The sawfly larva I showed here a couple of weeks ago has now been identified as Arge gracilicornis. This species feeds on Raspberry and Bramble leaves.

Light is our toy

Yet another day of wonderful light, so I went out several times during the day.

The patch of Phaeolepiota aurea has continued to expand (I think it might be a ring-forming fungus), and this mature specimen had dew on the cap surface:

A vertical close-up provides a nice abstract shot:

This Fenusa dohrnii sawfly larva was clearly visible as it mined the Alder leaf:

Yet another sawfly larva on Bramble:

This Autumn Hawkbit flower is just in the process of opening from the bud:

A couple of shots of the hoverfly Eristalis tenax on Smooth Hawksbeard:

Lovely eyes.