Melampyrum pratense, common cow-wheat, is a plant species in the family Orobanchaceae. The seed of the plant has an elaiosome, which is attractive to wood ants (Formica spp.). The ants disperse the seeds of the plant when they take them back to their nests to feed their young. The plant is an ancient woodland indicator, as the ants rarely carry the seeds more than a few yards, seldom crossing a field to go to a new woodland. M. pratense is a food plant of the caterpillars of the heath fritillary (Melitaea athalia), a butterfly.