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Summary Temperature, especially body temperature, is a very important factor in the lives of animals. Body temperature may be raised or lowered by the transfer of heat directly by conduction, or indirectly through the transformation of radiation into heat; it may also be raised by metabolism and lowered by the evaporation of water. These are the factors which determine the amount by which the body of an animal shall differ in temperature from the surroundings. In aquatic animals, only conduction and metabolic heat are important and the body could not therefore remain cooler than the water. On the other hand, the water acts as a very effective cooling fluid, especially in animals with a good branchial flow of blood, and after a change of water temperature, body temperature becomes steady again in seconds or a few minutes. With one exception all recent measurements show body temperature to be less than 1°C. warmer than the water, even in a large cod. Temperature measurements are open to many errors, and the century‐old belief that the tunny is warm‐blooded requires confirmation. Air, unlike water, is a good heat insulator. For land animals gains of heat through radiation and losses by evaporation are important; an environment at uniform constant temperature probably seldom or never occurs in nature and gradients of temperature in the animal body itself may be considerable. Evaporation of water may cool an insect by several degrees below the air around it, especially if the air is dry and the temperature is as high as 40° C. There is no reason to believe that this cooling is an active regulatory mechanism, even in the special case of the cockroach, though it may save the insect from heat‐stroke during a short exposure. The surface‐volume ratio is larger for smaller animals, heat intake varies with the surface, and water available for evaporation varies with the weight. Consequently, other things being equal, if a small insect keeps cool for long it may desiccate too much. Even for a large insect prolonged exposure to warm dry conditions may be more damaging than a similar exposure to moist conditions, because the animal dies from desiccation. Radiation, especially from the sun, is often an important factor which keeps insects' bodies warmer than the immediate surroundings, and differences of 5–15° C. have been recorded. The colour of an insect's cuticle is not a good indication of the degree to which it absorbs heating radiation. The metabolic heat developed by similar insects at rest is very roughly proportional to the surface area of the body; since direct and indirect heat exchange and evaporation of water are also related to surface area rather than to body weight, mere size of body should have little effect on body temperature under steady state conditions. In most comparisons of different species, of course, the constants to be applied to these factors will be dissimilar. Some insects can increase their metabolic rate enormously, and this power is used in elevating body temperature, especially before starting ...

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SummaryA method is described of estimating the total numbers and frequency distributions of adults of the Red Locust, Nomadacris septemfasciata (Serv.), in outbreak areas of hundreds of square miles, based upon counting the numbers that fly up in a two-yard strip in front of a moving vehicle. The method has proved itself valuable for indicating both immediate and future requirements for killing the locusts, but it requires refining for some research purposes.By this method, the importance has been clearly shown of the process of congregation of scattered adult locusts in forming emigrant swarms that could start a plague. The locusts do not congregate but actually disperse just before laying eggs.The total population in part (189 sq. miles) of the North Rukwa Outbreak Area (a self-contained area of 253 sq. miles) in Tanganyika Territory has been followed for four years. There are indications that a small migrant swarm contains 5–10 million locusts, that a total population in the whole of the North Rukwa Outbreak Area of 20 million locusts is unlikely to yield a migrant swarm, but that 50 million locusts could readily do so.In 1953, after poor rains, no natural mortality was detected between July and October by the assessment methods described. In 1957, after good rains, natural mortality of 70–90 per cent. was revealed by the same methods, although the dry season was not fully covered by the assessments.