Scymnus nubilus Mulsant and Coccinella undecimpunctata L. are two generalist aphidophagous predators abundant in herbaceous habitats. Coccinella undecimpuctata, a larger species, lays its eggs in uncovered clusters, whereas S. nubilus, a tiny species, lays its eggs singly and, possibly, in concealed sites. Reproductive strategies in ladybirds seem to be adaptive, allowing for the co-occurrence of both predators, apparently without interfering with each other. The aim of this study was to characterize the following oviposition strategies in S. nubilus and C. undecimpunctata: daily fecundity, effect of available sites on females’ fecundity and daily pace of oviposition. We hypothesize that the single-egg-laying strategist (i) is more dependent on the availability of concealed sites to oviposit and (ii) lays eggs closer to aphid colonies. We found that different levels of concealability sites allow S. nubilus to increase fecundity. Contrarily to C. undecimpunctata, in the absence of a suitable substrate to conceal their eggs, S. nubilus females refrain from oviposition. Scymnus nubilus prefers to hide its eggs beneath prey carcasses, while C. undecimpunctata is less selective concerning oviposition sites. Scymnus nubilus dilutes its fecundity effort through more oviposition sites and events, while C. undecimpunctata requires one event to lay its clusters. Our results showed that the smaller ladybird is more dependent than the larger one on habitat structural complexity to maximize its fitness and that laying single hidden eggs, mainly during the scotophase, confers a potential adaptive advantage to increase fitness.