The exotic true bug, Ischnodemus variegatus Signoret, was recently found feeding on the invasive grass Hymenachne amplexicaulis in Florida. The biology and host specificity of I. variegatus is unknown; therefore, we performed laboratory essays and field samplings. Eggs are laid and nymphs feed in tight spaces between the leaf sheath and the stem. Adults occur singly or mating in the terminal whorl of H. amplexicaulis and are recognized by a particular “M” at base of the wings. Mean developmental times at 28⁰ C in days were: egg 10.5, nymph I 9.8, nymph II 5.4, nymph III 5.3, nymph IV 6, nymph V 7.8. Mean developmental times at 23⁰ C in days were: egg 13.2, nymph I 11.9, nymph II 6.8, nymph III 6.8, nymph IV 7.7, nymph V 11.6. Adult longevity in days ranged from 10 to 106 and 14 to 131 for 28 and 23⁰ C respectively. In average, females oviposited over 44 day period and laid 204 eggs. Field and laboratory observations suggest that I. variegatus is strongly gregarious. Host specificity results from forty plants tested suggest that H. amplexicaulis is the preferred host for I. variegatus. Females where able to oviposit on the non-target plants Thalia geniculata (Marantaceae) and Panicum hemitomon (Poaceae). Laboratory and field collected data of host specificity are discussed in the context of the risks/benefits of using mass releases I. variegatus in Florida.