If it seems like clouds of mosquitoes are flocking your way every time you go outside, you may have only your genes to blame, NPR reports. In a new study, scientists working with identical and fraternal twins exposed pairs to groups of mosquitoes to see which sibling the insects preferred. While the blood suckers seemed to show no preference among the gene-sharing identical twins, they often showed a clear preference for one fraternal sibling over the other—a reaction scientists chalk up to the very different genes of fraternal twins. Scientists believe the mosquitoes are drawn to some odors more than others and hope to unravel which genes produce attractive and repellant smells in future experiments.