Misuse of chemical insecticides has resulted in high levels of resistance in insect pests as well as environmental damage. Insecticidal spider-venom peptides provide an eco-friendly alternative to chemical insecticides as they are fully biodegradable, potent to insect pests, but harmless to mammals, birds and fish. However, the development of spider toxins as bioinsecticides has been impeded by their presumed lack of oral activity. Therefore, the aims of this study were to develop an assay for efficiently testing the oral insecticidal activity of spider venoms, and to isolate and characterise new orally active toxins. Fruit flies (Drosophila melanogaster) and sheep blowflies (Lucilia cuprina) were selected for screening 56 arachnid venoms. 71.4% of these venoms displayed high oral toxicity in fruit flies, and 30.4% were lethal to blowflies by oral application. The most two orally active peptide toxins, Pi1a and Avsp1a, were isolated from venom of the tarantulas Pamphobeteus insignis and Avicularia cf aurantiaca, respectively. We determined the structures of Pi1a and Avsp1a using NMR spectroscopy and used whole-cell patch-clamp electrophysiology to examine their impact on ion channel currents in American cockroach dorsal unpair median neurons. Both Pi1a and Avsp1a have the capacity to translocate across the insect midgut epithelium, and we show that this is mediated by endocytosis. Overall, our results indicate that oral insecticidal activity is more widespread in arachnid venoms than expected, and that Pi1a and Avsp1a are both promising candidates for bioinsecticide development.