Immature Stages of Drilidae
Detailed information on immature stages of Drilidae is being acquired. However, Clausen noted some detail about this family, stating that the larvae of subsist almost entirely on snails. Some species show a remarkable sexual dimorphism, the males being winged and females apterous and larviform (Clausen 1940/62).
Drilidae oviposit in large masses in shallow burrows in the soil. Females are able to produce 300-500 eggs, and sometimes the entire quota is laid in a single day. There is a large range in the exceptionally long periods of incubation recorded for the different species, varying from 6 weeks to 3 months.
First instar larvae are generally similar in appearance to the larvae of other Coleoptera. They are very active in their search for their snail prey. When a snail is located, the anal sucker takes a firm hold on the shell. The prey is then taken to some sheltered place, after which the larva enters the shell. The snail's operculum often proves to be a difficult barrier for the larvae. Feeding is gradual as compared with lampyrid larvae on the same hosts, and the snail may not die for many days after the larva has entered the shell. There do not seem to be any digestive juices or toxic fluids introduced into the snail's body during this early feeding. The mature larva is greatly distorted and twisted, due to confinement in a spiral cavity. Drilus flavescens Rossi appears to have a distinctive resting stage, induced by adverse conditions such as food shortage and adverse weather, which is comparable to the coarctate stage of Meloidae (Crawshay 1903). The integument of this stage is thin, nearly white, and largely bare, and the head and body appendages are rudimentary. They return to the active feeding stage when favorable conditions prevail. Pupation is within the snail's shell.
The life cycle from egg to adult takes 3-4 years; during which time 2-4 snails may be consumed each season. The larva molts after completion of feeding on each host and immediately before it abandons the shell. Adult beetles appear in late spring and early summer (Clausen 1940/62). Early accounts of the life history and behavior of D. mauritanicus Lucas and Malacogaster passerinii Bass were given by Cross (1926, 1930).