Sawfly Caterpillars?

[borderglider]

I found these caterpillars on a birch tree in my garden. I posted them on FLICKR and somebody suggested that they were probably sawfly larvae. They were quite small - about 2 cm long and they had this dramatic defence behaviour of arching their tails when anything cast a shadow on them. Any help with ID would be great.



Thanks

[Paul mabbott]

I'm not an expert and you find several sawflies on birch trees especially Croesus septentrionalis. Your picture looks most like the American species Croesus latitarsus - I don't know whether that's found in UK?

Yes, strange that defensive mechanism - quite a few larvae do that - I saw it earlier in the year with pine sawflies.

Originally Posted by borderglider

I found these caterpillars on a birch tree in my garden. I posted them on FLICKR and somebody suggested that they were probably sawfly larvae. They were quite small - about 2 cm long and they had this dramatic defence behaviour of arching their tails when anything cast a shadow on them. Any help with ID would be great.

[Laurence Clemons]

They are sawfly larvae although the leaf photographed is not a birch. There are several species which have larvae patterned as in the picture and which demonstrate the defensive behaviour shown. The only way to ensure a correct identification is to rear them to the adult stage. This may take 2-3 weeks or up to 10 months. The best way of rearing is to place a sample of the food plant with larvae in a container of dry, sharp sand. When the larvae have pupated remove the plant material and any faeces and leave in a cool environment.

[borderglider]

Thanks Laurence,
I assure you that the leaf in question is a Birch - Betula Jacquemontii - Himalayan Birch - honest! Anyway, the photo was taken last summer - if they return again I will try and give them a home till they pupate - though what a sawfly looks like I have no idea.

Graham

[Laurence Clemons]

Originally Posted by borderglider

Thanks Laurence,
I assure you that the leaf in question is a Birch - Betula Jacquemontii - Himalayan Birch - honest! Anyway, the photo was taken last summer - if they return again I will try and give them a home till they pupate - though what a sawfly looks like I have no idea.

Graham

Thanks for the clarification- the leaf was obviously not Silver Birch. As Paul says they could be a Croesus. I have reared C. septentrionalis from similar-looking larvae found on Alder Alnus glutinosa. These pupated soon after collecting and adults emerged within a month.

[valleyreefs]

i have exactly the same species on my silver birch...knew it was some form of sawfly and this is the first exact match i have found via google....only noticed them today and they are already stripping the tree bare (only 3 year old).....i am wales north of swansea (in the valleys isnt it) if location helps ......

have been looking at a way to alleviate myself of these without harming any other wildlife around me as i have several nests and a hedgehog in the garden, not to mention my dogs...the best things i have found so far which both claim to be organic are Rotenone (otherwise known as derris) or pyrethrum...bit worried about the affect they may have on beneficial insects though...if anybody can answer asap i would appreciate it as i need to rid these critters before loosing my tree

[Paul mabbott]

I think that would be over-reacting. Birch (like oak, hornbeam &c) are often attacked en masse by sawflies, moths, bugs but I have never seen even a single tree killed by them. It could happen, perhaps, with an isolated (young?) tree such as yours but I doubt it. I have often seen trees totally denuded early in the year - they simply make more growth later in the year (and probably more seed). I really wouldn't apply any biocides - they might kill the sawflies but so what? You would also certainly be killing a lot of other insects, some of which might, eventually, have controlled the sawfly!

[borderglider]

Interestingly, the new generation of sawfly larvae arrived on my Himalayan birch two weeks ago. There never seem to be 'thatt' many of them - they strip a couple of twigs of their leaves and that is about it. The bluetits take care of them - I think - and since they are heavily massed on a single leaf - about 20 caterpillars to one leaf - you could simply dunk the leaf in a pail of soapy water - or spray them with soapy water. Alternatively, snip off the worst infested leaves and put them on the bird table. Breakfast for robin chicks. If you don't use pesticides you will encourage a good 'balance' in your garden; the birds need these larvae to feed their young - if you kill all the larvae the birds go elsewhere - which removes your daylong 'watch team'. Once the birds stop patrolling, you will get larger explosions of larvae - and so on.

[valleyreefs]

i will try natures way first...hadn't thought of removing them and placing them on the bird tables...actually thought their vivid colouration would have discouraged birds......unfortunately the robins have already flown from here, as have the blue tits but i do however have several colonies of house sparrows between myself and next door plus some local starlings, so these guys will get a tasty treat today. (make a change from meal worms)...didnt really want to use pesticides but was worried about the welfare of the tree as its in its 3rd year here and has really come on this season....thanks for your help

almost forgot, will i need to protect myself with gloves whilst handling or are they pretty safe??

[Mrs Wibbly]

That picture looks exactly like the two dozen caterpillars I have just picked off my 'Betula utilis jacquemontii Doorenbos'. They had already cleaned all the leaves off one branch and had moved onto the next. They are now wandering around in the tray of my bird feeder!

As my tree is only 3 years old I was concerned that just a small group of these could strip it bare in no time at all so I will be out to inspect the tree again tomorrow.

btw - the leaf in the photo looks just like my tree and as far as I am aware this Betula is a "Silver Birch"

Also found a photo on Wiki under Sawfly.