Simulium, the biting pest and vector of human onchocerciasis, is best controlled by the regular use of larvicides—DDT in particular—in the streams and rivers in which the immature stages develop1. The speed of reinfestation after the application of larvicide suggests that Simulium eggs are not affected by the doses usually applied2. Partly because of the difficulty of finding eggs3, ovicides have never received serious consideration for Simulium control. Because we have repeatedly found egg masses of Simulium ornatum in field breeding streams in Surrey, we have been able to investigate the effects of a range of potential larvicides against eggs in the laboratory. Our findings, with technical details, will be reported fully later, but the following is a summary of our results.