Brachinus species are called bombardier beetles because of their habit of ejecting from the anus a glandular secretion that literally explodes when released, producing a popping sound. This secretion is foul-smelling and irritating, and serves as a means of protection. Aphididae The aphids constitute a large group of small, softbodied, insects that are frequently found in large numbers sucking the sap from the stems or leaves of plants. Such aphid groups often include individuals in all stages of development. They secrete a defensive fluid.
Aphids also excrete honeydew, which is emitted from the anus.
The honeydew consists of excess sap ingested by the insect, to which are added excess sugars and waste material. Honeydew is a favorite food of many ants, and some species of aphids are tended like cows by certain species of ants. One of the most important predators, is the ladybird beetle.