Many plants exude substances to repel insects. These howls are used to repel intruders and attract family members. Secreted protein can either repel or attract specific neurons. While hydrophobic polymers beneficially repel water and contribute to chewiness, they also detrimentally attract oil. Insecticides are distinct from non-insecticidal repellents, which repel but do not kill. Ions of like charge repel each other, and ions of opposite charge attract each other. Carthage mustered an army to repel Numidian forces. Like charges repel each other and unlike charges attract each other. In charge repulsion, particles that possess the same like electrostatic charges repel each other. The demons pursue, but the armies of Wisdom repel them. A semiochemical is a message-carrying chemical that is meant to attract, repel, and convey information. Alkanes are said to be hydrophobic as they repel water. Because protons are positively charged, they repel each other. They repel an attack later that night. The opposing currents will repel each other as a result.