SUMMARY1Insects which are parasitic alike on grasses, cereals, and other crops will, when these latter are unavailable, take up their quarters in the grasses and plants growing in the situations herein mentioned and, when the crops are again available return to them and commit their ravages.2Observations were conducted over a period of nine months on certain insects which attacked both grasses and cultivated crops in a limited area in Shropshire, viz. the farm of the Harper Adams Agricultural College, near Newport, and the immediate neighbourhood.3The observations indicate a danger of harbouring pests among the vegetation on headlands, hedgerows and waste places; grasses in particular, being susceptible to their visitation, are decidedly important factors in tiding pests over from season to season and this in itself suggests the advisability of keeping hedgerows and headlands clean.