Observations in the laboratory on the larva of Glossina tachinoides and G. submorsitans show that in both species it is slow in crawling and burrowing and often cannot burrow at all. It penetrates coarse sand more readily than fine, and fine sand than wood ash, and burrows easily in fine sand with pebbles. In nature it probably always burrows eventually, unless it is attacked by predators or parasites to which its behaviour renders it vulnerable.

Previous field work indicates that the depth to which the larvae burrow influences the effect of predators and parasites and sometimes of solar radiation on the puparia. Records of breeding-places suggest that larvae often crawl over hard soil to reach suitable places in which to burrow, and that unless the female fly, before depositing a larva, carefully selects such a place, the mortality due to other insects is probably high.