The spermatozoa of Solenopsis invicta are long and slender, measuring about 70 mum in length, of which the head region measures approximately 13 mum. The head consists of an acrosome formed by an acrosomal vesicle covering a perforatorium and a nucleus. This latter measures about 12 mum, has compact chromatin, and many translucent areas. The flagellum consists of an axoneme of 9+ 9+ 2 microtubules that begins just below the nuclear base. The two mitochondrial derivatives are of almost equal diameter, and there are two accessory bodies. The nucleus is attached to the flagellum by a centriolar adjunct located between the baso-lateral region of the nucleus and the anterior mitochondrial derivative extremities. Therefore, the nucleus-flagellum transition region of the spermatozoa of S. invicta is very similar to that of other ants and differs from the first description of this species [Ann. Entomol. Soc. Am. 67 (1967) 632]. In relation to other aculeates, it is possible that three characteristics (type of centriolar adjunct, presence of paracrystalline areas in each mitochondrial derivative, and the position of these areas within each derivative) may be autopomorphies for the Formicidae. (C) 2002 Elsevier Science Ltd. All rights reserved.342124128