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.

Sunny August

In this shot I tried to show the extensive Fuchsia hedging that paints much of western Ireland red at the moment, but the very bright sunshine made a decent shot very tricky.

Fuchsia hedging at Mongorrey

Note the very straight road stretching all the way westwards to the horizon. I had always thought that these long straight roads must be Roman roads, but the Romans never got this far, and the roads are known as 'Famine roads'.

The white umbellifer plants at the front of the shot are Angelica.

Many of the wasps that can be seen slowly crawling over umbellifers at the moment are males:

Male Vespula rufa

Vespula rufa can be identified by a combination of features including the red areas on the abdomen, facial markings and stripes on the thorax.

This Chloromyia formosa soldier fly was happily nectaring on the Angelica......

Chloromyia formosa soldier fly

until a Tenthredo sp. sawfly decided it would make a good meal and jumped on it:

Chloromyia formosa escaping from a Tenthredo sp. sawfly

Even at 1/120th of a second, the fly is just a blur.

It's not only the flowers of Angelica that attract insects: leaf-miners are also present. Phytomyza angelicastri is one of two species that I find locally:

Phytomyza angelicastri on Angelica

The Hawthorn parasite Taphrina crataegi clearly has some special habitat requirements. This is the only tree that I have found to be infected on my patch:

Taphrina crataegi on Hawthorn

I have also found it in one location in Northern Ireland, and in each case the tree overhangs lying water, but I know of many Hawthorns in similar situations that are unaffected, so it must be something more subtle.

As I was searching along a verge, a shadow passed over me and I looked up expecting to see a bird, but it turned out to be a huge Common Hawker dragonfly which was hunting along the same verge. I followed it for a while and it eventually rested on a Willow, so I managed to squeeze in a few distant shots:

Common Hawker dragonfly

And nearby I saw a Common Darter landing on a grass stem. She tolerated me for quite a while before flying off:

Common Darter dragonfly (female)

Slender St. John's Wort is my favourite flower, so I made an artistic crop of this pair:

Slender St. John's Wort

Gap between the showers

The Chrysomelid beetles are making a fine mess of the Willow leaves, only days after they have fully opened. This is Lochmaea caprea, and is confined to Willow.


Last week I showed Creeping Cinquefoil. This is its very close relative - Tormentil. Amazingly, I still have 3 species from this family to show in the near future.


As soon as the rain stops, the insects are back out cleaning themselves ready for their next flight. This is one of the Tenthredo sp. Sawflies. These are all strictly vegetarian as larvae and many are voracious predators as adults.


The wonderful, minute micromoth Glyphipterix simpliciella is one of the few to have a common name - Cocksfoot Moth. Its larvae live inside the stems of Cocksfoot grass and it is all of 4mm long. Check that on a ruler.


An amazing shot of a dead Holly leaf having been pierced in two places by the shoots of Horsetail, and being hoisted like a banner. The plant to the rear is Meadow Buttercup.


The end of a hoverfly. This spider had caught the fly and was in the process of beginning to wrap it up.


I have an expanding patch of purest white Bush Vetch in just one area. It appears to breed true from seed. I wonder when a sport like this becomes a (sub)species in its own right.