Identify these anyone?

I've had to really brighten this photo and enlarge it so you can see these things.  They are holding gatherings on my crocosmia leaves.

They look and behave like tiny tiny very fast moving caterpillars, are black and the only thing I can compare them in size to are chocolate vermicelli that people sprinkle on cake icing.  Each one is about 10mm in size.  In this photo they are grouped on the leaf in about a one inch square.

Anyone know what they are?  I brushed them off with my hand - but should more groups of them appear - are they considered foe or ought they to be left to go forth and prosper? 

I bet they are the larvae of something but don't suppose they'll be identifiable until they get bigger. Perhaps you could carefully cut off a leaf with some on, then put it in a jar of water with cotton wool or similar around the neck of the jar to stop them falling in. Enclose the whole lot in a plastic bag with small holes for ventilation. Wait and see what grows. Fascinating!

Hi jude5.  Wouldn't mind trying your suggested experiment - only thing stopping me trying it is that this particular crocosmia is a division from last year and it's grown so well that I'm hopeful it will flower this year.  The parent plant which I took the divisions from isn't looking hopeful for any flowers and had been failing for years so I don't want to go cutting pieces of leaves off if I can avoid it.  However, will see how things go.  It's a very tempting idea though.   We're scheduled to have forecast warning downpours tomorrow so if the little blighters appear any day after that I might just delve into the jam jar stock and do a little wildlife science!

Any news yarrow2? I'd love to know, can't resist a mystery! 

Hi jude5.  You might get an extra reply here.  Typed a response, leaned on something and my answer disappeared.  So I'm back again.

No, no news.  Been torrential rain for days and on quick paddle round the garden there's no sign of them.  Imagine the rain would have sluiced them off if they were continuing their crawling forays.  But - there are some small rust marks on some of the leaves and a some torn holes of irregular (not round) shape - so it may be that they did some work and disappeared off when the showers really hit.  Slugs and snails everywhere but no sign of the little black beasties.

If only the rain would stop, everything is floppy but foliage verdant with little blooming going on - other than some begonias which have held up amazingly well.  Will get back if the opportunity for the experiment arises. Thanks.