Black Legged Tick (IMAGE) Colorado State University Caption The blacklegged or deer tick, no bigger than the size of a period at the end of this sentence, transmits Lyme disease. Credit Centers for Disease Control and Prevention Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.