A study of the first 24 instars of the garden symphylan shows that antennal segmentation increases as each animal molts. A first instar has six antennal segments, whereas 24th instars have a maximum of 59 segments. First instars have maximum weights of 0.009 mg and lengths of 1.0 mm; 24th instars have maximum weights of 1.22 mg and lengths of 6.0 mm. Ninety-five per cent mortality occurred within 3 hours in soil cultures exposed to relative humidities between 58 and 75% if the soil surface of each culture was not covered by a succulent lettuce section. The same mortality occurred within 13 hours in lettuce-covered cultures exposed to similar humidities. At 95% relative humidity, 95% mortality occurred in 313.5 hours; in covered cultures, in 2 months. At 98 and 100% humidities, no symphylan desiccation occurred in uncovered or covered cultures. The results obtained in the humidity tests demonstrate the importance of relative humidity in maintaining large symphylan populations in the root feeding zone of infested soil, and also, the way in which succulent plant materials may aid in creating more favorable microenvironments for garden symphylans.