The diet depends on seasonal availability with such plants as Acacia, Casuarina and grasses being favoured.[29] They also eat insects and other arthropods, including grasshoppers and crickets, beetles, cockroaches, ladybirds, bogong and cotton-boll moth larvae, ants, spiders and millipedes.[29][48] This provides a large part of their protein requirements.[49] In Western Australia, food preferences have been observed in travelling emus; they eat seeds from Acacia aneura until the rains arrive, after which they move on to fresh grass shoots and caterpillars; in winter they feed on the leaves and pods of Cassia and in spring, they consume grasshoppers and the fruit of Santalum acuminatum, a sort of quandong.[4][50] They are also known to feed on wheat,[51] and any fruit or other crops that they can access, easily climbing over high fences if necessary.[49] Emus serve as an important agent for the dispersal of large viable seeds, which contributes to floral biodiversity.[50][52] One undesirable effect of this occurred in Queensland in the early twentieth century when emus fed on the fruit of prickly pears in the outback.