One of the most remarkable features of the locust season during the summer and autumn of 1930 in the Sudan was the unexpected and widespread occurrence of Locusta migratorioides, R. & F. Swarms, which laid eggs over a large extent of the country, entered from the west and south-west during July and August. There is no evidence of any of these swarms having been produced within the Sudan, and the place of origin of all the early swarms was without doubt situated outside its boundaries. There is evidence that breeding continued later in the southern portions of the country, particularly in the upper reaches of the White Nile (N. Lat. 5°), and movements of swarms were reported during the winter, but no reliable observations were made on the nature or extent of these activities. Only one brood was produced in the northern and central Sudan (probably north of N. Lat. 11°), and by October all locusts bred in these parts had either migrated away in swarms or had scattered. Migration took place in the case of the gregarious phase produced by large bands of hoppers. Where, however, bands of hoppers had been broken up by poisoning, or in cases where the bands were very small, the adults did not migrate. The absence of further breeding in the northern Sudan must be connected with the absence of winter rains and suitable vegetation.