Hello Barbara
These pests sound horrible and I do not know them. But it has been a tricky winter for lettuce and mine in the tunnel have suffered some losses, from a rotting of the stem, to do I think with a combination of freezing and then fungal rot. The worst affected are an earlier sowing of 1st September, (compared to 8th September) and I have lost more in the less ventilated, damper bottom tunnel, although both tunnels have had some doors open night and day.
Apart from that, and a few plants of Red Frills suffereing the same fate, the survival rate is impressive.