_Natural hosts._--_Blattella germanica_, on shipboard (Sundevall, 1831); Germany (Aclogue and Fowler, _in_ Burr, 1899a); on steamship "Samui" (Stamm, 1936); on cruiser "Duguay-Trouin" (Barbier, 1947); Hawaii (Williams, 1946a): This last record was based on a specimen dissected from an adult German cockroach collected on an airplane from the South Pacific. The parasite was reported as _Ripidius_ sp. by Williams, but Weber (1948) made the specific identification. _Ectobius pallidus_? Abeille de Perrin (1909) stated that _R. pectinicornis_ was first described by Sunders [sic] as _blattarum_ because it had been captured in the body of _Ectobia livida_. We presume that Abeille de Perrin was referring to Sundevall's work in which the host was given as _Blattella germanica_. _Periplaneta americana_, on shipboard (Sundevall, 1831): One nymph only. With the exception of the single nymph of _P. americana_, _R. pectinicornis_ apparently attacks only adult females and nymphs of _B. germanica_. Barbier (1947) found only _B. germanica_ parasitized, although both _Blatta orientalis_ and _Supella supellectilium_ were prevalent on board the ship. Primary larvae of the parasite failed to parasitize _Supella_. _Adult behavior._--The winged male is relatively active compared to the apterous female; it runs around, flies well, and jumps on the female when in her vicinity. The female remains stationary and lays eggs around her by bending her long ovipositor (Sundevall, 1831). The eggs (50-100) are laid among a network of silk fibers secreted by the female. The female dies after completing oviposition (Barbier, 1947). _Development._--The eggs hatch after 14 days, and the primary (triungulin) larvae ascend the host's legs to its body; the larvae then cut the intersegmental membrane between the metasternum and first abdominal segment of the cockroach, in order to enter the host's abdomen (Barbier, 1947). Chobaut (1892) first suggested this method of attack by the ripiphorid larva. As the parasites develop, the abdomen of the host becomes swollen. Developing larvae apparently eat the host's fat body, leaving the vital organs until the last. Parasitized female hosts were sterile and the eggs, when formed, never hatched. Development of the oötheca was also inhibited. There were usually two larval parasites per host, but three or four were found several times (Barbier, 1947). Sundevall (1831) found only one larva per cockroach except one host which, when crushed, yielded five. Stamm (1936) found three hosts infested with five larvae each. In a little over 100 cockroaches, Stamm found 10 that were parasitized.