Diaspores of myrmecochorous plants as food for certain spiders

Spiders eating diaspores (seeds and fruits) from myrmecochorous plants – i.e. those adapted to distribution by ants – is recorded here for the first time as a new case of herbivory in these typical predators. Having found seeds of Costus dubius (Afzel.) K. Schum. (1904) trapped in the web of a Parasteatoda spider (Theridiidae), tests with available myrmecochorous seeds and spiders in the greenhouses of the Botanical garden of the P. J. Safarik University in Kosice (Slovakia) were carried out. Parasteatoda spiders can actively collect C. dubius seeds near their webs and feed on them for a long time. Diaspores with elaiosomes (nutrient-rich appendages) from five other myrmecochorous plant species thrown directly into webs of Parasteatoda sp. and Uloborus plumipes Lucas, 1846 (Uloboridae), another spider species very abundant at this location, were also consumed. These initial observations show that the special chemical composition of elaiosomes, which imitates insect prey primarily for ants, can be attractive for some spider species too. Considering the tested taxa, in the case of Uloboridae contact with such food sources is improbable in their typical niches. However, at least some Theridiidae could also consume myrmecochorous diaspores in nature, especially if they are near source plants or paths of ants transporting these diaspores.