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(1) Background: the low-affinity calcium uptake system (LACS) has been shown to play a crucial role in the conidiation and formation of adhesive nets and knobs by nematode-trapping fungi (NTF), but its involvement in the formation of constricting rings (CRs), mechanical traps to capture free-living nematodes, remains unexplored. (2) Methods: we investigated the function of two LACS genes (<i>DdaFIG_1</i> and <i>DdaFIG_2</i>) in <i>Drechslerella dactyloides</i>, an NTF that forms CRs. We generated single (<i>DdaFIG_1Ri</i> and <i>DdaFIG_2Ri</i>) and double (<i>DdaFIG_1,2Ri</i>) knockdown mutants via the use of RNA interference (RNAi). (3) Results: suppression of these genes significantly affected conidiation, trap formation, vegetative growth, and response to diverse abiotic stresses. The number of CRs formed by <i>DdaFIG_1Ri</i>, <i>DdaFIG_2Ri</i>, and <i>DdaFIG_1,2Ri</i> decreased to 58.5%, 59.1%, and 38.9% of the wild-type (WT) level, respectively. The ring cell inflation rate also decreased to 73.6%, 60.6%, and 48.8% of the WT level, respectively. (4) Conclusions: the LACS plays multiple critical roles in diverse NTF.