WHY DO LADYBIRDS LAY EGGS IN CLUSTERS

1. Hypotheses that have been proposed to account for egg clustering in insects, and in particular the idea that it might be a defence against predators, were tested using the two-spot and seven-spot ladybirds, Adalia bipunctata and Coccinella septempunctata. 2. Clusters of eggs were not more viable than single eggs and, when supplied with an abundance of food, groups of larvae were not more viable and did not develop faster than single larvae. 3. Clustered eggs were not less vulnerable to cannibalism than single eggs. 4. Single eggs, however, were more likely to be eaten by predators than eggs in clusters and predators were more strongly deterred from attacking clusters than single eggs. 5. The strength of the deterrent effect associated with mixed species egg clusters was a function of the proportion of non-conspecific eggs in the cluster.