Un-identified grubs

[David Shaw]

I have found these grubs in my home made potting compost and have not seen them before. The compost contains loam, leafmould and grit so I would think that the loam is the most likely source. The loam is made from lawn turf which was dug and stacked several years ago. I have been using the stack for years and not found the grubs before. They are very difficult to spot in the compost and these specimens have been washed off under the tap. They have a rather leathery skin but the grubs that I know as leatherjackets are mush fatter than these.  I have tried my own web searches but while I can find plenty of illustrations of invertebrates there are very few of the larvae.

[ranunculus]

If you lived in the States, David you would be able to use this superb resource:-

http://www.ipm.iastate.edu/ipm/icm/indices/insectsandmites.html

[David Shaw]

Useful site, Cliff, but not really worth moving for 

[ranunculus]

 

[Anthony Darby]

Fly or perhaps moth larvae. Not welcome in a potting compost.

[David Shaw]

Ah, Anthony, I was waiting for morning in NZ  . Would you care to risk a closer id or suggest any other web sites that might help? I am surprised at the lack of response from the Forum experts, obviously no one knows, and have just forwarded the picture to Garden Organic and the Soil Association.

[daveyp1970]

Could they be some sort of saw fly larvae?

[Anthony Darby]

They are the larva of the St. Mark's fly (Bibio marci). Interesting, as I was singing in the choir at St Mark's, Remuera yesterday (Sunday) morning. They are usually scavengers, but do eat plant roots. The grubs, not the members of the choir.

[Lesley Cox]

Are these the same as some pictured in another thread a couple of months ago or round about then. I thought they were leather jackets but they weren't, they were some kind of fly which was mentioned by name. A search (?) might bring them to light.

[Maggi Young]

Well done, Lesley... you may not have much success with the search... but you give me the clues and I then find it.....

Yup, same critters, I think.... http://www.srgc.org.uk/forum/index.php?topic=8164.0

[David Shaw]

OK, thanks for doing the search, Maggi. I don't think that my grubs are the same as Rob's because Rob's seem to be on the surface in the light and mine seem to avoid the light. At the moment I much prefer Anthony's suggestion of St. Mark's/Hawthorn Fly larvae as we do have quite a colony of these black flies with the freaky long, dangling legs around the garden. Trouble is, on the web, I can only find pictures of the adults, none of the larvae. Also, I do not hear any choral music coming from my grubs!!!!!

[Anthony Darby]

Here's a link: http://www.tuin-thijs.com/gnats-engels.htm

[Maggi Young]

Anthony and Armin thought they were of the same species  then, David. Also it was said that they could be found on the surface at that time of year. Seems likely they would  not want to be exposed at this time of year.

[David Shaw]

'K, I see where you are all coming from. I am prepared to go along with the Bibio sp. flies which may or may not be OK in the compost.  I spent an hour this afternoon 'cleaning' a gallon of said compost of these larvae. It seems that I have a lot more to do! Still, the small birds will be happy tomorrow.

[Maggi Young]

Better safe than sorry, I think, David.... it seems the little devils will happily chomp on plant roots if Wikipedia is to be believed: " larvae are known to be root damage pests of celery, asparagus, roses, saxifrages, lawn grass, lettuce and Polyanthus. They also feed on a very large number of plant species that are commercially unimportant."