Polysphinctine wasps are exclusively koinobiont ectoparasitoids of spiders and have the unique ability to manipulate the web construction behaviour of their hosts. Most interactions between polysphinctine wasps and spiders are species-specific. However, recent studies have predicted that these associations are not as narrow as previously thought. Therefore, records on the ecology and biology of new interactions are required to confirm this hypothesis. Herein, we report the Darwin wasp Hymenoepimecis pinheirensis manipulating the behaviour of the tetragnathid spider Leucauge argyra in an urban area in southeastern Brazil (Campinas, São Paulo). We monitored a population of L. argyra in 2021-24 and collected data on the biology of the wasp-spider interaction. Of a total of 5.416 spiders, 6.85% (N=376) were parasitised by H. pinheirensis, with a higher frequency of attack in young individuals. Eggs are laid anterodorsally on the spider’s abdomen and hatch after 2-3 days. The larva of H. pinheirensis has three instars and develops on the host over approximately 12 subsequent days. Between the second and third instar, the parasitoid induces the host spider to build a cocoon web with a reduced number of radii (some of them V-shaped), the absence of viscid lines and hub loops, and three-dimensional structures consisting of lines above and below the hub attached to multiple sites on the substrate. Here, we add a second host for H. pinheirensis and a second parasitoid for L. argyra, which helps to elucidate the entangled web of interactions involving polysphinctine wasps and spiders.