Nematodes of the Brevibuccidae family were stated among spiders of the Theraphosidae family (the South American species), which were bred in Poland. The first sign of infection was anorexia which led to gradually increasing lethargy progressed to a huddled posture. Additionally, a white discharge with nematodes between mouth and chelicerae was noted. All of the derived nematodes were morphologically identified and determined to the species Tarantobelus arachnicida. A molecular analysis covered amplification and sequencing of small subunit ribosomal RNA (18S rRNA). A post mortem examination demonstrated the presence of nematodes not only near the chelicerae, but also inside the intestine, hence the source of infection might be insects used as a food. The research showed that such kind of infection is an important disease, which poses a serious risk to the breeding spiders. To date there is no effective treatment, however, we demonstrated that usage of the Lugol’s solution seems to be promising.