It looks like Flea Beetle damage. Keep an eye out for tiny black hopping beetles. They are very fast. The link below has a few options for control(did a quick web search). I have found nasturtiums to be a good trap crop. Here is a link that might be useful: flea beetle control

Dear Tony and Len - Thanks for your advice. I'm beginning to think you're both right. I guess I thought that the plants were too close to our balcony to be inviting for a possum... but then again they DO nest in people's roofs! And at night they would not have much to worry about no matter how close they came. I thought that maybe snails did the deed, but I'll take your advice that it was just too much for snails to do all in one go. Thanks again guys - You have put me on the right track. Time to think about fencing off my precious plants :-) Regards Adrian

The youngsters look scary too. They're not too fast but will try to move and evade if one were to reach in and crush them using the fingers.

Louise Soil could be wet deep inside, even if top is dry. it all depends on what it consists of. Best way to find out is to use bamboo or other wood skewer or chopstick, that will reach deep down into pt. Extra water accumulates there, and it could keep your soil mix wet. It is impossible to guess what the bugs are without photo and sometimes even with photo :) I understand that it is very difficult to photo very small bugs. Could be springtails (they come in many different sizes, colors and shapes), soil mites, root aphids...and many. many more. It is possible for bagged soil to be infected, but bugs still need certain conditions they like to thrive and multiply. More organics in your mix and more water + higher temps and/or humidity, better environments there is for many bugs. Common advice is not to use things like worm castings in potting mix. They are great for gardens, not so much in containers. (from wiki): Springtails commonly consume fungal hyphae and spores, but also have been found to consume plant material and pollen, animal remains, colloidal materials, minerals and bacteria. ETA: I just looked up Ecothrive Charge. It is beetle poop - so you are adding more poop to your pots, together with worm poop. ..."Laboratory tests have shown that Charge consistently contains more than 450 million colony forming units of beneficial rhizosphere bacteria per gram! "... It also states: ..."Charge is a 100% naturally-produced potting soil enhancer ..." Soil enhancer is not fertilizer IIRC.