The aim of this chapter is to discuss the rates of survival and decline of plant and animal species worldwide, and thus to set in context the welfare of the species within Britain and Ireland. In order to consider the worldwide picture, we should first agree on how many species in total (of animals and plants and excluding bacteria) we are considering. There is an immediate difficulty, in that estimates vary hugely, from perhaps 30 million to maybe even more than 50 million different species. The reason for the huge variation lies with the number of insects in rainforest canopy. There is little doubt that the number of bird species in the world is close to 10 000, and the number of plant species is estimated to exceed 300 000, but the number of different kinds of small insects (the majority of which are ants) in the canopies of tropical rainforest is huge, and very hard to get to grips with. A determined entomologist called Terry Erwin has tried hard to come up with accurate estimates. Erwin’s technique has been to climb up into the canopy, release a fog cloud of dense insecticidal vapour and let it descend through the canopy. The resulting insect casualties are then caught in large plastic sheets covering the ground below. The challenge of counting the numbers of species caught, and relating it to the total numbers up there uncaught, has been to determine the percentage of the total caught that cannot be confidently ascribed to a known and already described species, and compute from that what percentage of those caught are new. Since the total of those already described is known, this can be multiplied up to estimate the total in existence by using the percentage figure of new and unrecognised species. This is clearly a difficult exercise, and the widely differing results obtained by repeat sampling in different forests largely explain the huge variation in the estimate of between 30 and 50 million different species.