Abstract.1. The number of common carabid beetles trapped‐irr a wheat field on a clay with flint soil from May to October in.1971–77 differed greatly:Harpalus rufipesandPterostichus melanariuswere numerous every year; but the appearance ofH.aeneus, P.madidus, Agonum dorsale, Nebria brevicollis, Notiophilus biguttatus, Bembidion lamprosandTrechus quadristriatuswas much more variable.2. The numbers caught were not correlated with rainfall. Catches of the large species were positively correlated with accumulated temperature above an assumed activity threshold of 5°C, whereas the smaller beetles were negatively correlated with accumulated temperature, suggesting that the danger of desiccation at high temperatures limits their activity.3. The egg‐laying periods of the commonest species were:B.lamprosandA.dorsalefrom late April to June; overwinteredP.melanarius, H.rufipesandH.aeneusin May and June, with the summer generation of these species and ofP.madidusfrom July to September;T.quadristriatusduring August and September;N.brevicollisfrom September to November;N.biguttatusandC.fossorlaid in the early summer and again in the autumn.4. A few male and femaleH.rufipesandH.aeneus, and one femaleP.melanariusandN.brevicolliswere each parasitized by a single tachinid larva; oneP.melanariuswas infested with a mermithid pa