The adult is a very small black wasp, approximately the size of a winged cotton aphid but more slender.  Females can be seen crawling about on the undersurface of cotton leaves in search of aphids to parasitize.  When a suitable aphid is found, the wasp curls its abdomen forward between its legs and ‘stings’ or lays an egg in the unfortunate host.  An individual adult can parasitize up to 100 aphids during its brief life.  Eggs hatch in 2-3 days, and the larval parasite begins feeding inside its aphid host before ultimately killing it.  The larval stage lasts about a week, and the pupal stage, which takes place inside the body of the host aphid, takes an additional 4-5 days.  Thus, the complete life cycle takes roughly two weeks.

During the early stages of parasitism, parasitized aphids appear normal.  As the developing parasitic larva grows larger, it eventually kills the aphid, causing it to swell and turn beige to tan in color.  These “aphid mummies” are readily recognized and provide an easily observed indication of parasite activity.  However, it is important to keep in mind that the actual level of parasitism is considerably higher than would be indicated by counting the percent of aphid mummies.  Once the percentage of mummified aphids reaches 10-20%, it’s a good bet that most of the aphids present on a leaf have been parasitized.  Upon reaching the adult stage, the wasp cuts a small circular hole near the back end of the aphid, emerges, and begins searching for aphids into which to lay its eggs.  Lysiphlebus overwinters inside its aphid host as a larva or pupa, and mummified aphids can be found throughout the year.